AQUACULTURE OF MARINE WORMS

Abstract: A method of controlling the time of sexual maturation of marine worms, the method comprising manipulating the photoperiod to which the worms are exposed. The invention also relates to a method of cyopreservation of marine worms, typically comprising immersing the worms in liquid nitrogen.

Description: AQUACULTURE OF MARINE WORMS This invention relates to aquaculture of marine worms and particularly though not exclusively methods for the cryopreservation of the larvae of marine worms and of controlling sexual maturation of marine worms. Marine bait worms are animals in the Class Polychaete of the Phylum Annelida or in the Phylum Sipunculida or are such other animals as may be generally referred to as worms which may be used as bait by anglers. Such worms are also used as feedstuffs for fish crustaceans and other organisms, for toxicity testing and for other scientific purposes. Naturally occurring supplies of marine worms are not inexhaustible and collection of marine worms has been recognised as a cause of serious environmental concern. Aquaculture of marine worms provides a sustainable source. However, the seasonal breeding cycle of marine worms hinders provision of a constant supply of worms throughout the year. Since the natural fecundity of female marine worms is very high, large numbers of fertilised eggs are available from time to time that are surplus to requirements and are usually wasted. According to a first aspect, the present invention provides a method of preserving polychaete worms as recited in Claim 1. According to a second aspect, the present invention provides a method of preserving polychaete worms as recited in Claim 3. According to a third aspect, the present invention provides a method of recovering polychaete worms as recited in Claim 11. Preferred features which may be used with aspects of the invention are set out in the dependent Claims. The invention may be used as part of a worm breeding program. An example of such a program is set out below: Step 1 - Production of fertilised eggs The larvae to be preserved by means of the invention may be derived from fertilisations of marine worms. The fertilisation may be carried out by mixing fertilisable eggs {primary oocytes, secondary oocytes or later stages) with active spermatozoa at such concentrations as are suitable to bring about a fertilisation reaction in virtually all of the available eggs or by natural spawning. The eggs to be fertilised may be suspended in sea water or in a salt solution of similar constitution or may be suspended in sea water after the fertilisation reaction has been carried out. The method of fertilisation and the stage of differentiation of the germ cells at the moment of fertilisation is known to vary between different species of worm. The method to be selected for the production of fertilised eggs must be appropriate for the species. The process may involve removal of germ cells from the body cavity of the male or the female worms when they have been observed to have cytological and physical characteristics known to be associated with the sexual and development maturity and ability to take part in a fertilisation reaction or secondly may involve treatment of the eggs with substances extracted from the nervous system or from other body tissues or with synthetic substances such as 8,11,14- eicosatrienoic acid which has been shown to have an effect on the processes of maturation of the germ cells of some species of worms. Step 2 - Rearing of the larvae to the staσe of development suitable for preservation by means of the invention The larvae to be preserved must be raised under conditions suitable for their development and will preferably have been grown in independent batches of larvae derived from one or a small number of fertilisations carried out at the same time according to the subsequent usage of the larvae which may require larvae of known parentage. The larvae will preferably be at the same stage of development when selected for preservation by the process. The larvae should be kept under clean though not necessarily sterile conditions in sea water or some similar and appropriate medium at densities sufficiently high to be economic but not sufficiently high as to cause mortality. Typically the larvae may be kept in shallow trays measuring 75 x 45 x 7 cm containing sea water to a depth of approximately 5 cm and containing approximately 50,000 larvae or alternatively may be suspended in plastic dust-bin like containers at densities of approximately 50,000 larvae per litre with gentle aeration of other method of stirring the sea water. The larvae should preferably not be fed and should preferably be reared to the stage of development at which feeding is about to be initiated and the lipid and other food reserves in the gut tissues have been absorbed or utilised. Step 3 - Selection of the larvae and concentration for preservation The larvae to be preserved should preferably be at a uniform stage of development as determined by microscopic examination. The larvae will preferably be at a stage of development where they have become capable of independent movement by cilia and/or by muscular action and may have reached a stage where three functional segments with erupted chaetae have formed but where the fourth segment has not developed to a stage where erupted chaetae are present and the larvae will preferably not have commenced feeding although the gut tissues may have reached a stage of development where the animals are about to begin feeding. The larvae may be concentrated by pouring them in the sea water or other medium in which they have been developing onto a nylon mesh sieve or similar device with a mesh spacing of approximately 64 microns or such other dimensions as may be suitable to retain the larvae but allow free movement of the water. A suitable sieve can be made by gluing plastic mesh to the edges of a plastic beaker from which the base has been cut or some similar device may be used such that the larvae can be introduced into a series of solutions and removed from those solutions on the sieve. The larvae will preferably be introduced on the sieve into a vessel containing a cryoprotectant mixture and from the sieve introduced into plastic straws, which may be coated with cholesterol or plastic bags, or foil bags or other such device as may be used with a controlled rate freezer. The time at which the larvae are introduced to the device in which the larvae will be cooled will be noted and the total duration from the time of the first introduction to the time at which the cooling protocol is made to operate will be controlled and will be part of the operational procedure. The cryoprotectant mixture may be one which contains various concentrations of Dimethyl-sulphoxide (DMSO) or 1,2 Propane diol with or without the further addition of non-penetrant organic agents which may aid the process and which may by preference be a solution of 1.5 Molar DMSO in sea water. In the event that the cryoprotectant agent is a solution of 1.5 Molar DMSO in sea water the total time to elapse from the introduction of the larvae to the operation of the protocol shall not normally be greater than ten minutes and may by preference be not greater than four minutes . Step 4 - Preservation of the larvae by low temperature dehydration The larvae will preferably be cooled at a predetermined rate that may normally be between 0.1 and 10 °C per minute with or without one or more periods of zero temperature change and the larvae will preferably be cooled to a temperature of between -25 and -35 °C depending on the rate of cooling used. The larvae may be unfrozen and arranged in the presence of a frozen cryoprotectant mixture which thus leads to the dehydration of the larvae prior to the subsequent rapid cooling of the larvae as for example by plunging to larvae into liquid Nitrogen. In the event that the cryoprotectant mixture contains 1.5 Molar DMSO in the presence of sea water, the temperature will preferably be such that less than 6% of the isotonic water content at equilibrium with sea water at 20 °C remains prior to the subsequent rapid cooling of the larvae as determined by the prior calculation of the volume of the larvae in equilibrium with an unfrozen solute with the osmolality characteristic of the terminal temperature with due allowance for the diffusion of water and permeability of the larvae. Ragworm Nereis (Neanthes) virens larvae may be preserved when at their nechtochaete stage of development in which three well developed parapodia bearing chaetae operated by muscles are present. The larvae will preferably be capable of movement and by preference they will not have initiated the formation of the fourth setiger or will have a rudimentary fourth setiger in which the chaetae have not erupted but may have developed beyond either of the above two stages of development. By preference they will also have developed the hind gut to the point where a lumen is present as indicated by a dark central line when observed through a microscope. Preserving the larvae at this stage in their development may enhance their ability to remain unfrozen in the presence of an ice cryoprotectant mixture, to be preserved and to be recovered. Step 5 - Transfer of the larvae to low temperature conditions and subsequent storage The larvae may be transferred to a temperature of -196 °C by plunging them in devices such as straws, ampoules , bags and other such devices in which they have been cooled into a vessel containing liquid Nitrogen or by some other means that would achieve cooling rates necessary to prevent ice formation and that would allow for the permanent maintenance of the larvae at temperatures at or near -196 °C. Step 6 - Recovery of larvae from low temperature conditions The larvae may be removed from the container at which they are maintained at or near -196 °C and held in a water bath at 20 °C or near that temperature for a short period until the frozen cryoprotectant mixture is observed to thaw. The larvae may be discharged from the device be it straw, ampoule, bag and other structure onto a sieve. The larvae may be introduced into a solution of sea water or other suitable medium of a volume approximately the same as the volume of cryoprotectant mixture in which the larvae were frozen and may be maintained in that solution for two minutes with gentle agitation prior to introduction of a second similar volume of sea water or similar medium for a further two minutes, after which time the DMSO or other cryoprotectant substance would be deemed to have diffused out of the larvae in sufficient quantity, and the larvae may be introduced into a large container of sea water suitable for the further growth of the larvae. The larvae may be washed twice by replacing the large volume of water into which they had been introduced with fresh sea water to remove final traces of DMSO or such cryoprotectant agents as might have been used. The larvae may then be maintained and reared to the stage at which they would be suitable for the specific purpose. The invention may be used to control the time of year at which marine worms grow and develop. This may also be achieved by the further aspects of the invention set out below. The invention also relates to a system of rearing worms under controlled conditions of relative day and night length in a twenty four hour day, the combination of a specific day and night length being referred to as the photoperiod, and controlled conditions of temperature which two systems of control can be used to provide sexually mature animals for the purposes of breeding throughout a greatly extended breeding season with or without the additional use of low temperature preserved larvae as an additional source of larvae whose effective birth date is outside the natural breeding season. According to a fourth aspect, the present invention provides a method of controlling the time of sexual maturation of polychaete (Polychaeta) worms as recited in Claim 12. This may be achieved by exposing the animals to a predetermined sequence of changes in photoperiod according to a sequence of protocols and may be under controlled temperature conditions. The progression of gametogenesis and other components of the sexual maturation process may be so changed that the time of sexual maturation process when breeding may be carried out may be different to that observed in similar animals not subject to such rearing protocols and which may allow for the carrying out of artificial fertilisations or the induction of spawning by chemical or other means at different seasons of the year other than that of the naturally occurring breeding season. This may be achieved by means of a system for maintaining such marine or estuarine worms under controlled conditions of light and dark to simulate 24 hour photoperiodic days in which the duration of the light and dark phases can be changed from short days defined as having a light period substantially less than 12 hours to long days defined as having a light period substantially greater than 12 hours or from long days to short days . Procedures that may be adopted may be described in a series of protocols of specified photoperiods and preferred temperature that will influence the time of sexual maturation and gamete development and shall subsequently influence the times at which the animals are in a suitable state for reproduction and which with or without further treatment to induce a state in which fertilisation is possible by decerebration or exposure to late acting signals may be used for the purpose of carrying out artificial fertilisations either by the extraction of the reproductive cells from the body cavity or by the induction of breeding by exposure to chemical agents known to induce spawning, In order to facilitate description the following terms are defined: Photoperiodic day: the total duration of a single sequence of light and dark; Natural photoperiodic regime: the annual sequence of photoperiodic days that occurs naturally at the location at which the animals are kept or the work is being carried out; Effective date of birth: the actual date of fertilisation of an animal or the date of recovery of the animal from a cryopreservation system; Photophase: the duration of a period of light in the photoperiodic day; Scutaphase: the duration of dark in the photoperiodic day; Critical photophase: the duration of a photophase which is such that any greater photophase will be interpreted as being a long day and which is such that any shorter photophase is interpreted as a short day and which, in the specific case of the reaction of Nereis (Neanthes) virens described herein is a photophase of 12 hours in a 24 hour day; Short day: a 24 hour photoperiodic day in which the photophase is substantially less than the critical photophase length ie { 11 hours for Nereis (Neanthes) virens for growth of eggs; Long day: a 24 hour photoperiodic day in which the photophase is substantially greater than the critical photophase ie ) 13 hours for Nereis (Neanthes) virens for growth of eggs ; Coelomic biopsy; a means of determining the state of sexual maturity of a worm; Modal diameter: the most frequent diameter of oocytes observed by coelomic biopsy; Mean diameter: the arithmetic mean diameter of oocytes observed by coelomic biopsy; Temperature: The temperature of the water in which the animals are maintained with an allowance for temporary fluctuations of around 2 °C above or below the specified temperature; Decerebration: The removal by surgical means of the supra- oesophageal ganglion. Embodiments utilising the present invention and relating to controlling sexual maturation of marine worms are described, by way of example only, in the following examples. Step 1 - Maintenance of worms prior to selection for the process Female and male worms may be maintained in sand (or some other suitable substrate) in boxes, tanks or other suitable container that is supplied with sea water at a temperature preferably in a range of 0 °C to 30 °C plus or minus 2 °C or may be obtained by collecting the animals from suitable natural populations . The system of maintenance may be provided with a filtration and aeration means to maintain the water in good condition for husbandry; temperature may also be controlled. Step 2 - Selection of worms for the execution of the process The worms to be introduced to the culture conditions may be selected by prior coelomic biopsy or other means and the stage of sexual development and/or the effective season of birth will normally be specified according for example to one of the procedures or protocols to be described. The selected animals may be animals at any stage of development from larvae to maturing female or male worms according to the protocols . The stage of maturity of a female worm may be determined by examining the primary oocytes in the coelomic fluid or in some cases by examining the primary oocytes retained in the ovaries that may be found in virtually all or in some instances only a small number of the segments. In the event that the worms are female worms in the family Nereidae, the oocytes may be sampled by withdrawing a small quantity of the body cavity fluid known as the "coelomic fluid" into a hypodermic syringe or, into a glass pasteure pipette that has a specially sharpened point or into a sharpened glass capillary. A volume of coelomic fluid containing some 50 to some 1000 oocytes may be withdrawn. In the event that the worms are male worms in the family Nereidae, the spermatocytes may be sampled by withdrawing a small quantity of the body cavity fluid known as the "coelomic fluid" into a hypodermic syringe or, into a glass pasteur pipette that has a specially sharpened point or into a sharpened glass capillary. A volume of coelomic fluid containing some 1000s of spermatocytes or spermatogonial clusters may be withdrawn. In the event that the worm is a member of a family of worms such as the family Nephtyidae or the family Polynoidae the examination of the oocyte diameter or the stage of development of the male germ cells may be carried out by a process of coelomic puncture and the removal of a small sample of the germinal tissue from the germinal epithelia which shall be associated with blood vessels in the body cavity or otherwise attached to the body wall. Step 3 - Maintenance in a specific photoperiodic regime In order to operate the procedures it will be necessary to have arranged conditions suitable for the maintenance of the animals under conditions of known photoperiod in which the photophase and the scutaphase may be different to those occurring naturally at the place of experimentation and the operation of the process. Containers such as tanks, concrete or brick constructions or any suitable construction or container in which marine worms may be kept should be arranged inside chambers of any suitable construction fitted with a source of tungsten or fluorescent or any other suitable light source connected to a manually or automatically controlled switch that allows the duration of the photophase and scutaphase to be controlled or alternatively the animals may be kept in containers fitted with lids which may be applied or removed manually or mechanically in order to control the ingress of natural or artificial light and by any of these means to control the duration of the light phase or in any similar arrangement that enables the duration of the photophase and scutaphase to be determined and controlled. The photoperiod and temperature protocol to be followed may be determined with reference to one or more or all of: i. the month of birth or the month of recovery from a preservation system, such period of recovery establishing the effective birth date; ii. the photoperiodic treatment received from the time of birth or effective time of birth; iii. the time of year and the ambient photoperiodical cycle; iv. the desired season for sexual maturation and breeding; v. the stage of gametogenic development of the animal. Step 4 - Assay of the progress of sexual maturation and development and selection of animals for breeding and the subsequent performance of artificial fertilisations and/or induction of breeding Worms to be selected for the purposes of breeding may be subjected to a process of examination of the stage of sexual development by a procedure involving coelomic biopsy or some other methodology as has been substantially described in Step 2. Females may be selected for the purposes of breeding by appropriate criteria relating to the size and morphology of the oocytes and which, if the female is a female of the taxonomic designation Nereis (Neanthes) virens may be selected to have the majority of primary oocytes with a diameter greater that 160 urn and having a cytological halo of clear cytoplasm in the cortical region, or which shall otherwise be recognised as being of a stage ready for fertilisation. Males may be selected for the purposes of breeding by appropriate criteria relating to the stage of cytological development of the developing germ cells which, if the male is a male of the taxonomic designation Nereis (Neanthes) virens may be selected by the presence of spermatozoa dissociated from the tetrads which characterise the previous stage of sexual development, or which otherwise are selected by criteria which indicate a readiness to become active in sea water with or without stimulation by maturation inducing substances, for example, 8,11,14 eicosatrienoic acid or such other substances as may be known to induce maturation of the sperm of polychaete worms as may be extracted from the supra-oesophageal ganglion or the body fluids. The inventors have determined that specimens of polychaete worms will respond to the effective day length to which they are exposed; that there is a critical photoperiod for this response which is a species and reaction specific photophase and/or scutaphase and which in the case of Nereis (Neanthes) virens is 12 hour light 12 hour dark in a 24 hour day; that the rate of oocyte growth is influenced by the effective day length; that the response is further moderated by real time, age and stage of maturity; and that the rate of oocyte growth determines the time at which the animals will reach a stage of sexual maturity or reach a stage at which they can become fertilisable or can be induced to spawn. The invention, in one of its aspects, relates to a series of operations by means of which specimens of polychaete worms, which may be the polychaete worm Nereis (Neanthes) virens may be induced to become sexually mature or otherwise fertilisable at times outside the natural breeding season. By combining a series of transitions between long days and short days and combining these transitions with exposure to an appropriate temperature it is possible to predict and to control the time of breeding of selected groups of worms. The procedures by which this may be achieved are large in number and can be set out as a series of protocols each of which may be designated to achieve a specified objective. A number of such protocols are set out herein. The examples of protocols given herein relate to the conditions and seasons of the Northern Hemisphere, in the Southern Hemisphere the effective dates, months and seasons would be the equivalent in the Southern Hemisphere solar cycle. Described below are a series of protocols which may be used to effect some predetermined change in the time of sexual maturation and subsequently the time of breeding of marine worms which may be worms of the family Nereidae and which may be worms of taxonomic designation Nereis (Neanthes) virens. Protocol I Protocol I is a procedure to be initiated in a time of naturally occurring long days, which in the Northern Hemisphere may be June, to induce accelerated oocyte growth. It may be used to provide females of worms which may be Nereis (Neanthes) virens suitable for breeding or induction of spawning at times in advance of the natural breeding season and which may be expected to be possible in the period from December to March or earlier. Animals having a birth date close to the natural breeding season (which in the event that the worms are Nereis (Neanthes) virens would be March/May) or which had a birth date outside that period and were maintained under ambient photoperiodic conditions as found in the natural environment from the time of birth or recovery from a system of preservation and which will have been maintained under such an ambient (natural north temperate) photoperiodic regime or a simulated photoperiodic regime with "long days" (photophase ) 12 hours) from the time of their birth to mid-September and "short days" (photophase { 12 hours) from mid-September to mid-March and thereafter to the onset of the illustrated Protocol under "long days" at any suitable temperature for the encouragement of growth and preferably in the region of 20 °C. The Protocol consists of a sequence of transfers from conditions of long days to conditions of short days from any period when the day length is long which may be for example May onwards at convenient (eg monthly) intervals. The temperature conditions to which the animals are transferred should be suitable for the development of the oocytes and, in the event that the females are female Nereis (Neanthes) virens the temperature may conveniently be 15 °C or lower and may by preference be in the region of 8 °C. The transfer from long days to short days may be by an instantaneous change from a photophase of 16 hours to a photophase of 8 hours or any sequence of progressive shortening of the effective photophase from greater than 12 to less than 12. In the event that the animals to be treated by the Protocol are female Nereis (Neanthes) virens they may be selected by coelomic biopsy to have a modal oocyte diameter in the range of 40-120 um at the time when the Protocol is initiated. By the end of the period of naturally occurring long days all the animals subject to the Protocol will have been exposed to short day conditions and may be maintained at temperatures not greater than 15 °C and preferably below 12 °C until the time of breeding. The animals will be re-examined by coelomic biopsy at any convenient interval, the purpose being to select those animals that have reached a stage of readiness for breeding. Females with the modal oocyte diameter greater than 160 um and a distinct clear cortical halo or having such other observable criteria to indicate a readiness to undergo fertilisation may be selected for breeding and/or the induction of spawning. Male worms with developing germ cells at the tetrad stage of development or with freely dissociated spermatocyte or spermatid cells or with bundles of spermatozoa associated in sperm morulae or which have such other criteria as to suggest a readiness to take part in a fertilisation reaction and yield viable embryos may be selected for breeding and/or the induction of spawning. Protocol II Protocol II is a Protocol to induce breeding in specimens of Nereis (Neanthes) virens and similar worms which have a semelparous life history and which do not in nature breed until two or more years old and which may not breed in captivity until they have reached such an age, and in which it would be desirable to induce breeding at some period in advance of that that would occur naturally as for example in May to July. The Protocol may be suitable to induce such breeding in female Nereis (Neanthes) virens that would not otherwise breed until they approach an age of two years . The Protocol would be initiated soon after the naturally occurring date of the critical photoperiod which is 21 September in the Northern Hemisphere for Nereis (Neanthes) virens. The Protocol may be initiated in October or November and would be used to provide females suitable for breeding in the period from April to July of the following year. Females selected for treatment in a manner similar to that described for Protocol I herein will be selected by coelomic biopsy to have a modal oocyte diameter less than 120 um or to be immature as being indicated by the absence of germ cells in the coelomic cavity in the early autumn period eg during October when it would normally be expected that such animals would not breed in the immediately following spring. Suitable females for treatment with the Protocol may be female Nereis (Neanthes) virens and will generally have a birth date prior to May of the same year and, if reared in captivity, will have been maintained from birth under long day conditions at temperatures suitable for growth and preferably greater than 12 °C and preferably at a temperature of 20 °C. According to the Protocol groups of such females will be transferred from long days to short days at some convenient intervals eg monthly intervals from September to January and simultaneously to temperatures of 12 °C or less than 12 °C or to conditions of decreasing temperature to reach a temperature less than 12 °C within eight weeks of transfer and at a stepwise rate of decrease in temperature of not more than 2 °C per week. They will subsequently be maintained under conditions of short days and low temperature less than 12 °C. From April onwards the animals will be examined by coelomic biopsy and females selected for breeding according to the size and the morphology of the coelomic oocytes and males selected by the appearance of tetrad stage germ cells or free spermatozoa in the coelomic fluid. Protocol III Protocol III is designed to provide females for breeding in the period September to November. Animals having a birth date in December (as may be achieved by other Protocols described herein) or having an effective birth date as determined by recovery of larvae from low temperature in or before December will have been reared under simulated ambient conditions for the first year of life as if the birth date was in April ie in long days for a period of about five to six months then to short days for a period of some five to six months and then to long days for a variable period according to the desired time of breeding and maintained under these conditions for a period of not less than one month but which may be a period of several months and which subsequently will be transferred to short days. At the time of this transfer the animals will also be maintained at a temperature suitable for the maturation of germ cells such as a temperature of 12 °C or a temperature below 12 °C but above 4 °C. Animals will be selected for the purposes of breeding by the criteria set out in Protocol I and Protocol II. Protocol IV Protocol IV is designed to provide animals for breeding in the period from August to November. The Protocol requires prior provision of juveniles which are themselves the offspring of one of the previously described Protocols or alternatively and by preference larvae whose effective birth date has been changed by a process of suspension of development such as may be achieved by a programme of low temperature dehydration. The animals to be treated will have a birth date or date of recovery from a system of preservation prior to 31 January and the animals will be subjected to a long day and a temperature suitable for somatic growth which may preferably be 18 °C for a period of at least five months but which may be longer than five months after which period the animals would be transferred to conditions of short days and lower temperature which may conveniently be a temperature of 12 °C or lower than 12 °C and which may be a progressively reducing temperature. The animals will be maintained under the short day and low temperature conditions subsequently and examined by coelomic biopsy or similar treatment at convenient intervals. Animals suitable for breeding will be expected to have developed within six months of the transfer to short day conditions and will be selected by the criteria described in Protocols I and II. Protocol V Protocol V is an alternative means of achieving animals suitable for breeding in the period from July to September. Animals whose birth dates are close to the natural breeding season in April will be exposed to a simulated regime of day length as if they were born in December ie they will be exposed to short days but the animals will be maintained in temperatures to encourage somatic growth and in the event that the animals are Nereis (Neanthes) virens by preference a temperature of 18 °C for a period of three months from birth. They will then be exposed to long days and temperatures to encourage somatic growth and in the event that the animals are Nereis (Neanthes) virens by preference a temperature of 18 °C for six months then returned to short days and a low temperature or preferably a temperature between 5 and 12 °C for a period of up to six months. Following this sequence of transitions between photoperiods and regulation of temperature the animals will be selected for the purposes of breeding as described in the earlier described methods and Protocols. The Protocols described illustrate some of the very many Protocols which may be designed to incorporate the specific knowledge and the innovative step in order to achieve the desired commercial objective. In the event that the invention is used to provide juveniles of Nereis (Neanthes) virens throughout the year it will usually not be necessary for all of the Protocols described above to be used in order to achieve production of juvenile worms through the greater part of the year. Animals selected as being suitable for breeding purposes by reference, in the case of females to the specific diameter of the coelomic oocytes or, in the case of males, to the presence of tetrad stage spermatocyte cells may be further treated to induce fertilisability or the onset of spawning. Selected animals may also be decerebrated by the surgical removal of the prostomiu or of the posterior parts of the prostomium or such other parts of the central nervous system as may be indicated by the existing scientific literature using such techniques as may reasonably be used to remove the centres of neurendocrine influence during the final stages of maturation. The use of decerebration as a component in the novel and not previously envisaged circumstances described herein however has not been previously established as a technique for the realisation of the objective of breeding such worms outside the normal season of breeding activity. Animals selected for breeding purposes may also be exposed to different conditions of maintenance in the periods after selection as may be expected to induce them to become sexually mature and that in the event that the selected females are female Nereis (Neanthes) virens such exposure may be to long day lengths and a temperature in the region of 20 °C for a period of one to a few weeks after the female has been selected and prior to the induction of artificial fertilisations. Artificial fertilisations may be carried out by mixing oocytes that have developed a clear morphologically distinct halo with spermatozoa showing spontaneous activity when diluted in sea water. Spermatozoa that have been recovered from a cryopreservation system may be used. The animals may be fed a pelletised diet with high lipid and high protein content at a rate of 2.5% body weight per day until some two months prior to the anticipated breeding date when, in the event that the animals are members of the family Nereidae the diet may be reduced progressively to zero. Specific examples of the aspects of a number of the specified Protocols are given below. Example 1 - Induction of early sexual maturation (Protocol I) Step 1 Specimens of Nereis (Neanthes) virens were selected from stocks of females raised in captivity in a temperature regime of about 18 °C in beds of sand supplied with running sea water held constantly at this temperature by mixing natural sea water with that derived from a power station outfall that power station using sea water as a condenser coolant, and additionally maintained under natural ambient photoperiodic conditions from birth until the second June following their birth which was approximately 15 months earlier. Step 2 Samples of coelomic fluid were obtained by coelomic biopsy and in the case of females selected for the process and for the control treatment if the mean oocyte diameter was in the range 100-130 microns or, in the case of males, if spermatogonial platelets were present in the coelomic fluid. Step 3 The animals subjected to the process were placed into a short day photoperiodic treatment by enclosing them in concrete tanks with a sand substrate inside a building with wooden partitions and inside which there were tungsten lights subjected to time control and such that the light illuminated the beds of sand in which the worms were living and in the short day treatment the lights were switched on for a period of eight hours in each 24 hour period and at other times were switched off there being no other significant light entering the sheds and illuminating the beds of sand and the temperature of the sea water supplied to the tanks was no greater than 15 °C. For the purposes of comparison another group of animals selected at the same time and of the same stock was maintained under essentially similar conditions but the period of illumination was that of the ambient photoperiodic conditions being determined by the time of sunrise and sunset at that latitude at that time of year. Step 4 Coelomic samples were taken in October some three months after the time of transfer to short day conditions. Approximately 50 oocytes were measured from each animal subjected to the treatment or treated as a control group. A summary of the results is presented in Table 1 which shows that the mean oocyte diameter found in the animals subjected to the process was significantly greater than that of the animals not subjected to the process (see Table 1). This was evidence that the growth of the oocytes in the treated females was significantly greater than that in the non-treated animals. The animals were subsequently maintained in a photoperiod with short days and at a temperature less than 12 °C. By 21 December all of the animals subjected to the experimental Protocol had proceeded through the stage of sexual maturation, had spawned and died as is normal following the sexual maturation and spawning of these animals. None of the animals maintained under the ambient conditions photoperiodic conditions had completed sexual maturation and spawned at this time. Table 1 No of females 23 25 Table 1 - Mean oocyte diameter of the short day and ambient groups in October as a result of the treatment in Example 1. Example 2 - Photoperiod The following example illustrates the response of females to a variety of photoperiodic manipulations as may be included in a number of the above Protocols. Step 1 - Maintenance and origin of the worms The animals illustrating the process in this example were specimens of Nereis (Neanthes) virens raised in captivity in concrete beds supplied with sea water at an approximately constant temperature of 18 °C and fed on a proprietary diet and subjected to ambient photoperiods from birth to the onset of the Protocol treatments. The animals were all offspring of a single fecund mating known by the Inventors as genetic group 8.2 and had the same birth date of January 1994. Step 2 - Selection of the worms The animals were selected in November 1994 and at that time they were all observed to lack either coelomic oocytes or spermatocyte platelets in the coelomic fluid which is an indication that they would not under normal circumstances or the circumstances of culture at 18 °C be expected to breed in the following Spring. Nereis (Neanthes) virens is a semelparous organism that breeds only once, and that breeding being normally in March or May would be expected to complete the processes of vitellogenesis during the period from September to December in the Autumn preceding the year in which the individuals would complete sexual maturation and thus be ready for the purposes of breeding or ready to complete the process of spawning in the following Spring. Step 3 - Maintenance in a specific photoperiodic regime The animals selected for the procedure were introduced to plastic boxes supplied with sea water from a recirculating sea water system in a marine laboratory each box being inside a wooden construction fitted with fluorescent tube lights controlled by electronically operated time switches. The constructions being such that no other light illuminated the plastic boxes inside which the worms were held. The plastic boxes were supplied with a substrate of sand in which the animals made burrow systems and the animals were fed daily with a proprietary feed during times of natural daylight and when the fluorescent light tubes were switched on. The temperature of the sea water being supplied to the boxes was held throughout the period of operation of the photoperiodic Protocols at 17 °C. Three different photoperiodic treatments are illustrated in this example: treatment A, treatment B and treatment C. The observations were made for the purpose of designing Protocols and the treatments do not necessarily relate to any one of the specific Protocols described herein. Treatment A Selection of females in November 1994. Exposure to long day lengths in the equipment described at a temperature of 17 °C for a period of three months until February 1995 and subsequently maintained in short days but remaining at a temperature of 17 °C until examination on 24 May 1995. Treatment B Selection of females in November 1994. Exposure to short day lengths from November to January, then subsequent exposure to long day lengths until examination on 24 May 1995 and held at a temperature of 17 °C throughout. Treatment C Selection of females in November 1994. Exposure to short day lengths from November to April, then transfer to long days from April onwards and maintained at a temperature of 17 °C throughout. Treatment C represents a simplified mimic of the ambient cycle of photoperiod but with constant temperature at 17 °C. Step 4 The effectiveness of the treatments was evaluated by means of measurements of oocyte frequency distributions for individually treated animals obtained by coelomic biopsy as in Example 1 and carried out in May 1995. Approximately 25 randomly selected oocytes in a sample of coelomic fluid of each female were measured using compound light microscopial observation. The results are shown in Tables 2A, 2B and 2C which summarise the mean oocyte diameter data for animals subjected to each treatment. Table 2A Female no Sample Mean oocyte Standard diameter deviation (microns) 1 29 169 5.18 2 28 171 5.82 3 26 173 4.79 4 26 176 6.58 Mean 172 Table 2B Female no Sample Mean oocyte Standard diameter deviation (microns) 1 29 137 9.68 2 30 130 10.16 3 25 143 6.85 4 28 140 6.49 5 27 136 8.21 6 29 126 9.06 Mean 136 Table 2C Female no Sample Mean oocyte Standard diameter deviation (microns) 1 31 149 13.06 2 25 157 8.53 3 28 141 30.94 4 30 168 3.61 5 29 166 5.48 6 25 152 21.64 Mean 136 The data show the clear divergence in the rate of oocyte development induced by the exposure to the different day length treatments at a constant temperature, the females held in Treatment A being substantially more mature than those held in Treatment B and Treatment C. Example 3 - Temperature regulation The response of individual females to a change in day length is also influenced by the temperature at which the animals are maintained and therefore the Protocols devised and explained herein in some circumstances and for some purposes designate the temperature at which organisms should be maintained in certain specific circumstances. This example illustrates this aspect of a typical Protocol . Step 1 The animals illustrating the process in this example were specimens of Nereis (Neanthes) virens raised is captivity in concrete beds supplied with sea water at an approximately constant temperature of 18 °C and fed on a proprietary diet and subjected to ambient photoperiods from birth until the onset of Protocol treatments . The animals were all offspring of a single fecund mating known by the Inventors as genetic group 9.7 and had the same birth date, that birth date being 10 February 1995. Step 2 The animals were selected on 24 January 1996 using as the criterion for selection the observation of coelomic oocytes in a coelomic biopsy such that each animal selected was female and such that the modal and mean oocyte diameter of the coelomic oocytes were less than 100 microns. Step 3 The animals selected for the procedure were introduced to plastic boxes supplied with sea water from a recirculating sea water system in a marine laboratory, each box being inside a wooden construction fitted with fluorescent tube lights controlled by electronically operated time switches . The construction being such that no other light illuminated the plastic boxes inside which the worms were held. The plastic boxes were supplied with a substrate of sand in which the animals made burrow systems and the animals were fed daily with a proprietary feed during times of natural daylight and when the fluorescent light tubes were switched on. The temperature of the sea water being supplied to the boxes was initially 16 °C. The animals were exposed to a period of six weeks in which the photoperiod was a simulation of long days with the photophase being 16 hours and the scutaphase being 8 hours in duration. After a period of six weeks the boxed animals were subdivided into two groups for the purposes of illustration of the effectiveness of treatments that are incorporated into specific Protocols are described herein. Both groups were from this time exposed to the same photoperiodic regime which was exposure to simulated short days in which the photophase was eight hours and the scutaphase 16 hours but one group (Group 3A) was supplied with sea water at 16 °C and the other group (Group 3B) was supplied with sea water that was progressively cooled at a rate of 3 °C each month ie 13 °C in March, 10 °C in April and 7 °C in May. Step 4 The animals were re-examined at intervals including examination on 20 May 1996 and the diameter of oocytes in samples of coelomic fluid obtained by biopsy was measured and recorded. The results are summarised in Table 3. The animals have continued their sexual development and those in Group 3B are substantially advanced in sexual development and are indicating a readiness for spawning in July 1996. Example 4 - Decerebration In the event that the animals selected for the operation of the invented process are specimens of Nereis (Neanthes) virens. Step J. The animals illustrated in the process in this example were specimens of Nereis (Neanthes) virens raised in captivity in concrete beds supplied with sea water at an approximately constant temperature of 18 °C and fed on a proprietary diet and subjected to ambient photoperiods from birth until the onset of the Protocol treatments. The animals were all offspring of a single fecund mating known by the Inventors as genetic group 9.7 and had the same birth date, that birth date being 10 February 1995. Step 2 The animals were selected on 8 May 1996 such that each animal selected was female and such that the modal and mean oocyte diameter of the coelomic oocytes was between 100 and 120 microns. Animals with such oocytes subject to the photoperiodic conditions that occur in nature would cease to develop the oocytes and would not be expected to breed until the Spring of the following year, such timing being determined by the sequence of photoperiod and temperature as has been observed by the Inventors . Step 3 The animals selected for the procedure were introduced to plastic boxes supplied with sea water from a recirculating sea water system in a marine laboratory, each box being inside a wooden construction fitted with fluorescent tube lights controlled by electronically operated time switches. The constructions being such that no other light illuminated the plastic boxes inside which the worms were held. The plastic boxes were supplied with a substrate of sand on which the animals made burrow systems and the animals were fed daily with a proprietary feed during times of natural daylight and when the fluorescent light tubes were switched on. The temperature of the sea water being supplied to the boxes was in some cases 16 °C or alternatively 10 °C or 7 °C as set out in the summary of the treatments set out below. Additionally, one group of animals was subjected to a decerebration procedure in which the posterior part of the prostomium containing the supra-oesophageal ganglion was removed by surgical removal of the tissues in the prostomium in the region defined by the posterior margin of the prostomium and a line passing in front of the anterior pair of prostomial eyes. The surgical procedure was carried out in sterile sea water using iridectomy scissors. The animals were allocated to five experimental groupings as follows: Group A - exposure to short days and to a temperature of 10 °C Group B - exposure to short days and to a temperature of 16 °C Group C - exposure to long days and to a temperature of 10 °C Group D - exposure to long days and to a temperature of 16 °C Group E - exposure to short days and to a temperature of 7 °C. The development of the oocytes was followed in all the groups and differences observed between them as summarised in Table 4. Table 4 Group Group Group Group Group A B C D E No of females 14 12 6 7 5 surviving Mean oocyte 108 116 117 109 114 diameter (microns) 8.5.96 Mean oocyte 133 121 113 105 147 diameter (microns) 28.5.96 Fertilisation of No No No No Yes oocytes possible by July 1996 The observations illustrate the effectiveness of combining decerebration procedures with certain photoperiod and temperature sequences in order to achieve fertilisations of oocytes outside the breeding season. In this instance the fertilisations were carried out using spermatozoa of Nereis (Neanthes) virens recovered from liquid Nitrogen that had been preserved by a cryopreservation process. Embodiments utilising the present invention and relating to preservation of marine worms are described, by way of example, in the following examples. The embodiments of the present invention that are described may be applied to the larvae of the polychaete worm Nereis (= Neanthes) virens commonly referred to in the UK as the King ragworm. Example 1 - Preservation of the larvae of Nereis (Neanthes ) virens Step 1 Primary oocytes having a mean diameter greater than 190 microns and having a clear translucent halo and having first been tested with mature sperm to confirm that they had reached a stage of development where they were able to complete a fertilisation reaction and to subsequently develop to the nechotochaete stage were removed from the coelomic fluid of a female specimen of Nereis (Neanthes) virens raised from birth under conditions of commercial production at a temperature in the range 18-20 °C throughout life and under ambient photoperiod conditions . The primary oocytes numbered approximately 300,000 were mixed with coelomic fluid taken from a male worm having dissociated spermatozoa which would become active and show forward movement following dilution in sea water in a volume of one litre. Step 2 Five minutes after the addition of the sperm containing fluid to the sea water containing the primary oocytes the sperm/oocyte mixture was further diluted with filtered sea water and transferred to a series of trays containing sea water to a depth of 3 cm and diluted such that the number of larvae did not exceed 5,000 larvae per 2 . The larvae developed in the covered trays under a photoperiod of 121:12D for a period of ten days at a temperature of 12 °C without feeding or the addition of food of any kind. Step Samples of larvae were taken at random from the population of larvae developing in the trays and the stage of development determined by examination through a binocular microscope. The larvae were observed to have a well developed gut with rather small lipid droplets in which the lumen can be distinguished as a distinct central line. The larvae were observed to have three pairs of chaetigers with erupted chaetae and only a very rudimentary fourth chaetiger in which the chaetae had not erupted and the larvae had not started to feed. The larvae were concentrated for the purposes of the process on a nylon mesh sieve which had been constructed by gluing 64 micron netting onto a rigid transparent plastic tube with a diameter of 2 cm and which was ideally suited for treating relatively small numbers of larvae. Step 4 The concentrated larvae were suspended in sea water at a concentration of about 1000 larvae per ml. The larvae in sea water were mixed with a solution of DMSO in sea water such that the final concentration of the DMSO in sea water/DMSO mixture was 10% by volume. This was achieved by mixing one volume of sea water/larvae with three volumes of 13.34% DMSO by volume in sea water. The mixture containing the larvae was drawn into 0.5 ml plastic straws and loaded onto a device for holding such straws and introduced into the cooling chamber of a controlled rate freezer. The total time elapsed from the first introduction of the larvae to the DMSO containing sea water mixture to the operation of the cooling process was three minutes . The straws were taken to a start temperature of 20 °C and then cooled according to the following protocol. The larvae were cooled from the start temperature of 20 °C at a rate of 5 °C per minute to a temperature of -5 °C and then cooled at a rate of 0.3 °C per minute to a temperature of -25 °C. Three straws were introduced to the chamber of the controlled rate freezer during a period not greater than three minutes each straw and the larvae in them having been subjected to the same procedural steps. In this way each straw was considered to constitute a replicate treatment. Step 5 The straws were removed from the chamber of the controlled rate freezer and dropped into liquid Nitrogen in a glass lined vacuum vessel and after rapid cooling in this way introduced into a numbered container in a large dewar containing liquid Nitrogen in which the larvae were to be stored. Step 6 After one week, and on the same day, each of the three straws was removed from the numbered container and defrosted by holding the straw in a water bath at 20 °C until the ice core in the straw was observed to melt. The end of the straw was then cut and the liquid and larvae discharged into an equal volume of sea water in a glass vessel. After two minutes a volume of sea water equal to the volume of the combined cryopreservation mixture/sea water/larvae mixture was added. After a further two minutes the mixture was added to a large volume (about one litre) of sea water in a clear plastic aquarium tank. After two minutes the larvae were removed from this large volume of sea water by pouring them gently over a 64 micron sieve and added to a similar volume of fresh sea water. The procedure was repeated and batches of the larvae numbering approximately 200 larvae per batch were maintained in sterilised sea water at a density of about one larvae per ml in glass vessels at 12 °C for a period of seven days . On the second day after feeding the larvae were fed by the introduction of 5 ml of a live culture of tetraselmis soeccia. The containers were stirred and observed daily and the water replaced and the larvae fed again on the third day. The total number of larvae recovered from the straw was determined for each straw after three hours. After a period of seven days the total number of larvae capable of independent movement that were clearly alive and that were showing signs of further differentiation of the fourth setiger was determined and the survival rate calculated as the number of such larvae as a percentage of those observed to be present after three hours. The results of these examinations are summarised in Table 1. Replicate Total no of No of larvae Observed Code No viable larvae alive and survival observed capable of rate % three hours movement on after removal day seven from liquid Nitrogen 1 120 55 45.8 2 206 109 52.9 3 90 23 25.6 Total 416 187 45.0 Example 2 - Preservation of the larvae of Nereis (Neanthes) virens Steps 1 to 3 The larvae selected for Example 2 were identical in origin to those used in Example 1 and the same procedures were followed for Steps 1 to 3. Step 4 The concentrated larvae were suspended in sea water at a concentration of about 1000 larvae per ml. The larvae in sea water were mixed with a solution of DMSO in sea water such that the final concentration of the DMSO in sea water/larvae/DMSO mixture was 10% by volume. This was achieved by mixing one volume of sea water/larvae with three volumes of 13.34% DMSO by volume in sea water. The mixture containing the larvae was drawn into 0.5 ml plastic straws and loaded onto a device for holding such straws and introduced into the cooling chamber of a controlled rate freezer. The total time elapsed from the first introduction of the larvae to the DMSO containing sea water mixture to the operation of the cooling process was three minutes. The straws were taken to a start temperature of 20 °C and then cooled according to the following protocol. The larvae were cooled from the start temperature of 20 °C at a rate of 2.5 °C per minute to a temperature of -35 °C and then held at that temperature for one minute. Three straws were introduced to the chamber of the controlled rate freezer during a period not greater than three minutes each straw and the larvae in them having been subjected to the same procedural steps. In this way each straw was considered to constitute a replicate treatment. Step 5 The straws were removed from the chamber of the controlled rate freezer and dropped into liquid Nitrogen in a glass lined vacuum vessel and after rapid cooling in this way introduced into a numbered container in a large dewar containing liquid Nitrogen in which the larvae were to be stored. Step 6 After one week, and on the same day, each of the three straws was removed from the numbered container and defrosted by holding the straw in a water bath at 20 °C until the ice core in the straw was observed to melt. The end of the straw was then cut and the liquid and larvae discharged into an equal volume of sea water in a glass vessel (solid clear glass watch-glass). After two minutes a volume of sea water equal to the volume of the combined cryopreservation mixture/sea water/larvae mixture was added. After a further two minutes the mixture was added to a large volume (about one litre) of sea water in a clear plastic aquarium tank. After two minutes the larvae were removed from this large volume of sea water by pouring them gently over a 64 micron sieve and added to a similar volume of fresh sea water. This procedure was repeated and batches of the larvae numbered approximately 200 larvae per batch were maintained in sterilised sea water at a density of about one larvae per ml in glass vessels at 12 °C for a period of seven days . On the second day after feeding the larvae were fed by the introduction of 5 ml of a live culture of tetraselmis soeccia. The containers were stirred and observed daily and the water replaced and the larvae fed again on the third day. The total number of larvae recovered from the straw was determined for each replicate straw after three hours. After a period of seven days the total number of larvae capable of independent movement that were clearly alive and that were showing signs of further differentiation of the fourth setiger was determined and the survival rate calculated as the number of such larvae as a percentage of those observed to be present after three hours . The results are summarised in Table 2. Replicate Total no of No of larvae Observed Code No viable larvae alive and survival observed capable of rate % three hours movement on after removal day seven from liquid Nitrogen 1 222 192 86.5 2 162 116 71.6 3 159 129 81.1 Total 543 437 80.48 Example 3 - Preservation of larvae of Nereis (Neanthes) virens and subsequent recovery from conditions suitable for commercial production Step 1 A female specimen of Nereis (Neanthes) virens raised from birth under conditions of commercial production at a temperature in the range 18-20 °C throughout life and under ambient photoperiod conditions and fed on a proprietary food was selected for the purposes of provision of larvae for preservation by means of the invention . The primary oocytes of the female were observed by coelomic biopsy to have a mean diameter greater than 190 microns and having a clear translucent halo. A sample of the oocytes was removed by coelomic biopsy using a hypodermic syringe fitted with a suitable needle and mixed with a small sample of spermatozoa diluted in sea water to establish that the oocytes were capable of undergoing a fertilisation reaction as is characteristic for this species . The sample of oocytes was further maintained for a period of ten days to ensure that the fertilised eggs were capable of development to the stage were they had developed three pairs of parapodia with erupted chaetae (the nechtochaete stage) and this having been confirmed the females were used as a source of oocytes which after fertilisation would provide a source of juvenile worms for the purposes of the procedure. The fertilisation was carried out in the following way: A sample of approximately 2 ml of coelomic fluid was taken from a male in which dissociated spermatozoa were observed to be numerous in the body fluid. The sample of the coelomic fluid was introduced into a sample of sea water approximately 100 ml in volume. An aliquot of this sea water sperm mixture with a volume of about 25 ml was introduced into a sample of sea water such that the final volume was approximately 250 ml. The primary oocytes of the selected female numbering approximately 750,000 in total were caused to be released into the sea water sperm mixture where they would come into contact with the spermatozoa and be fertilised virtually instantaneously. A sample of the oocytes was examined to confirm that a high proportion of the oocytes (virtually 100%) exhibited the slightly elevated fertilisation membrane that is evidence that a fecund fertilisation reaction has taken place and the oocytes were diluted into a volume of five litres of sea water. Samples of this fertilised egg/sea water suspension were taken for the purposes of estimation of the total number of eggs present. The eggs were subsequently transferred to shallow trays in five litres of sea water at a density of 20,000 fertilised eggs per tray. Step 2 The larvae developed in the trays for a period of ten days at a temperature of 12 °C without feeding or the addition of food of any kind. Step 3 On the tenth day after having been fertilised the larvae were concentrated by pouring the sea water and larvae mixture through a sieve constructed by gluing 64 micron mesh to a suitable length of domestic UPVC piping with an internal diameter of 15 cm. A total of 70,000 larvae were so concentrated. A number of larvae suitable for introduction to a total of 12 x 0.5 ml plastic straws at a maximum density of 2,000 larvae per straw was introduced to a volume of 13.8% DMSO in sea water such that the final concentration of DMSO was 10% by volume and the resultant mixture was introduced into twelve plastic straws within a period of three minutes and loaded onto straw holders suitable for the appliance that was to be used for the purpose of cooling the larvae. Step 4 The straws were taken to a start temperature of 20 °C and then cooled from the start temperature of 20 °C at a rate of 2.5 °C per minute to a temperature of -35 °C and then held at that temperature for one minute . Step 5 The straws were removed from the chamber of the controlled rate freezer and dropped into liquid Nitrogen in a glass lined vacuum vessel and after rapid cooling in this way introduced into a numbered container in a large dewar containing liquid Nitrogen in which the larvae were to be stored. Step 6 After a period of one month (about thirty days) a total of thirty six straws containing cooled larvae were removed from liquid Nitrogen in batches of eight straws. Eight straws were defrosted at 20 °C in each batch treatment and the contents of the eight straws discharged into glass measuring vessel and an equal volume of sea water was added. After two minutes a further equal volume of sea water was added and after a further two minutes the mixture was poured over a nylon sieve and the larvae retained on the sieve washed into a large volume (about five litres) of sea water in the clear plastic aquarium tank. After two minutes the larvae were removed from this large volume of sea water by pouring them gently over a 64 micron sieve and added to a similar volume of fresh sea water. This procedure was repeated until a total of thirty six straws had been defrosted. After three hours the number of viable larvae was determined by counting the numbers of larvae found in a subsample of one micron taken from a litre of sea water in which the larvae had been dispersed by agitation. The larvae were transferred to shallow trays at a density of 12,000 larvae per tray and approximately five litres of one micron filtered but non-sterile sea water per tray. After two days the larvae were fed by the introduction of a quantity of Tetraselmis soeccia. The larvae were stirred and agitated by lifting the trays twice per day and the sea water was changed and the larvae re-fed on the third day. The larvae were maintained at 12 °C for a period of seven days and after this period subsamples were taken to determine the approximate proportion of animals that had recovered and were apparently viable. The subsamples showed that approximately 70,000 larvae had been recovered from liquid Nitrogen and that of these larvae approximately 35,000 had survived and were apparently viable having continued to be capable of movement, of feeding and commencing the process of chaetal sac differentiation in the fourth chaetiger. On the seventh day after the initial recovery from liquid Nitrogen the surviving 35,000 larvae were transferred as a single batch to conditions suitable for their subsequent growth for commercial purposes for the supply as bait to the sea angling bait markets by introduction into a concrete bed with a total area of 2 m 2 . The larval worms were fed and maintained at 18-20 °C under long day (L:D 16:8) photoperiodic conditions. After a period of seven weeks from the time that the larvae were introduced to the concrete tanks three sub- samples of the animals were taken by means of the insertion of a circular plastic core device with an area of 0.00785 m 2 . The worms in the sub-samples were recovered by repeatedly shaking the sand mixture with sea water and pouring the mixture after a few minutes over a 64 micron mesh sieve as might be conveniently be used to recover small animals from a sand water mixture. The number of animals recovered was determined. For two of the samples the mean length of the animals recovered when relaxed in 5% ethanol sea water was determined by measuring all of the intact animals present. The number of segments present in the undamaged surviving animals was determined. These observations were made for the purpose of establishing whether or not the animals had developed subsequently under conditions of culture suitable for commercial purposes such as for ongrowing for the purpose of supply of ragworms for use as bait by sea anglers and in a manner comparable to juvenile worms that had not been subjected to the preservation process. The numbers of animals recovered are shown in Table 3. Sample Number 1 37 2 40 3 46 Mean No 41 Standard Deviation 4.58 Bed Area = 2 m 2 Sample Area = 0.00785 Estimated total no of 10,445 survivors The data obtained by examination of the animals in samples 1 and 2 are shown in Table 4. Sample 1 Sample 2 Length No of segment Length No of segment 0.8 39 1.5 43 1.7 31 1.3 50 1.4 40 1.2 42 1.8 42 0.8 30 1.6 29 1.0 36 1.5 36 0.7 40 0.7 42 1.1 41 0.8 40 2.0 29 0.9 35 0.6 35 1.2 45 1.9 24 1.0 24 1.5 30 1.1 39 1.3 36 1.3 44 1.2 27 1.9 46 1.5 41 1.3 37 1.6 36 1.5 41 1.1 38 0.7 26 0.7 45 1.7 0.4 25 0.7 n=17 0.5 31 1.3 mean=38.12 1.0 43 0.8 sd=5.80 1.1 44 0.6 1.5 43 0.7 1.4 1.3 0.7 n=22 0.5 1.1 mean=36.77 0.4 0.8 sd=7.15 0.6 0.7 0.5 1.2 1.0 1.0 1.1 0.6 1.3 n=30 1.1 mean=l .08 0.7 sd=0.429 0.4 0.5 n=36 mean=1.04 sd=0.424 The rate of growth and the rate of segment proliferation indicate that the animals recovered from liquid Nitrogen had developed at a rate that is not different from that of animals otherwise produced growing under such conditions. The number of animals recovered indicates that the mortality of the animals has not been different from that of animals otherwise produced introduced at this age into similar conditions .

Claims: CLAIMS 1. A method of preserving polychaete (Polychaeta) worms comprising rapidly cooling larvae that have developed to a stage at which they have three well developed parapodia bearing chaetae. 2. A method in accordance with Claim 1 in which the larvae are preserved prior to reaching a stage of development at which their fourth segment has developed to an extent that erupted compound chaetae are present . 3. A method of preserving polychaete (Polychaeta) worms comprising rapidly cooling larvae that have developed to a stage at which they have a differentiated gut with a lumen. 4. A method in accordance with Claim 3 in which the larvae have not introduced food to the lumen of the gut. 5. A method in accordance with any preceding Claim in which the larvae are substantially without ingested food. 6. A method in accordance with any preceding Claim in which the larvae have used substantially all of the lipids in the gut. 7. A method in accordance with any preceding Claim in which the larvae are subjected to a low temperature dehydration prior to the rapid cooling. 8. A method in accordance with any preceding Claim in which the larvae are subjected to a process which leads to vitrification upon rapid cooling. 9. A method in accordance with Claim 8 in which the process is carried out at room temperature. 10. A method in accordance with any preceding Claim in which the rapid cooling is carried out by plunging the larvae into liquid Nitrogen. 11. A method of recovering larvae preserved by a method in accordance with any preceding Claim comprising removing the larvae from cryogenic storage. 12. A method of inducing the time of sexual maturation of polychaete worms outside the natural time for maturation comprising exposing the worms to a photoperiodic regime substantially different to the natural photoperiodic regime. 13. A method in accordance with Claim 12 in which the worms are maintained in a controlled temperature regime. 14. A method in accordance with Claim 12 or Claim 13 in which the worms have an effective date of birth other than during the natural breeding season. 15. A method in accordance with any one of Claims 12 to 14 in which the worms are recovered from a preservation system. 16. A method in accordance with any one of Claims 12 to 14 in which the worms have been induced to breed outside the normal breeding period. 17. A method in accordance with any one of Claims 12 to 16 in which the photoperiodic regime to which the worms is subjected is substantially equivalent to the natural photoperiodic regime but is displaced in time relative to the natural photoperiodic regime . 18. A method in accordance with Claim 17 in which the photoperiodic regime to which the worm is exposed is displaced by substantially three months relative to the natural photoperiodic regime. 19. A method in accordance with Claim 17 in which the photoperiodic regime to the worm is exposed is displaced by substantially six months relative to the natural photoperiodic regime. 20. A method in accordance with any one of Claims 12 to 16 in which the photoperiodic regime to which the worms are exposed is one in which the duration of a period of short days is substantially greater than that occurring in the natural photoperiodic regime. 21. A method in accordance with any one of Claims 12 to 16 in which the photoperiodic regime to which the worms are exposed is one in which the duration of a period of long days is substantially greater than that occurring in the natural photoperiodic regime. 22. A method in accordance with any one of Claims 12 to 21 in which during a period of short days the photophase is constant. 23. A method in accordance with any one of Claims 12 to 21 in which during a period of long days the photophase. 24. A method of inducing sexual maturation of polychaete worms having a natural breeding season in the Spring to a time substantially in advance of that by exposing the worms to a change from long days to short days in advance of the time when the change from long days to short days occurs in the natural photoperiodic regime. 25. A method of inducing sexual maturation of polychaete worms having a natural breeding season in the Spring to a time substantially later than that by maintaining the worm exposed to short days beyond the time when the change from short days to long days occurs in the natural photoperiodic regime. 26. A method in accordance with any preceding Claim in which the worms are members of the order Phyllodocida. 27. A method in accordance with Claim 26 in which the worms belong to the Nereidae family. 28. A method in accordance with Claim 27 in which the worms are of the species Nereis (Neanthes) virens. 29. A method in accordance with any one of Claims 1 to 25 in which the worms are members of the order of Eunicida. 30. A method in accordance with Claim 29 in which the worms belong to the family Eunicidae. 31. A method in accordance with Claim 30 in which the worms are members of the genus Marphysa. 32. A method of accordance with any one of Claims 12 to 31, in which the worms are decerebrated as part of the method. 33. A method in accordance with any one of Claims 12 to 32, in which the worms are subjected to temperatures of 5-10°C. 34. A method substantially as described herein. 35. A worm that has been subjected to a method substantially as described herein.

Inventors: OLIVE PETER JAMES WILLIAM, OLIVE, PETER, JAMES, WILLIAM
Applicants: OLIVE PETER JAMES WILLIAM, SEABAIT LIMITED, OLIVE, PETER, JAMES, WILLIAM
Application year: 1997
Main classification: A01K67
IPC codes: A01K67