bluuebunny/crossref_metadata_2025 huggingface dataset:
Aspects of the morphology and ecology of some unusual deep‐sea eels (Synaphobranchidae, Derichthyidae and Nettastomatidae) from the eastern North Atlantic
Authors: Merrett N. R. , Saldanha L.
Published: January 2006

Specimens of Haptenchelys texts (9), Ilyophis arx (3), I. brunneus (36) (Synaphobranchidae), Nessorhamphus ingolfianus (5) (Derichthyidae), Nettastoma melanurum (9) and Venefica proboscidea (3) (Nettastomatidae) have been studied from collections in the eastern North Atlantic. An additional two V. proboscidea were also included from eastern South Atlantic material. The samples were used to augment the incomplete descriptions of these scantily known species, in order to allow further clarification of their taxonomic status. Data from the three synaphobranchid species have been used to clarify the sub‐familial relationships and provide a preliminary family diagnosis. They have also been incorporated in an annotated key to the identification of the species found in the area. In an addition, all the specimens have provided supplementary information on the ecology of the various species, in aspects of distribution, both horizontal and vertical, diet and reproduction.
Group size and patch location by the stoneloach, Noemacheilus barbatulus, a non‐visually foraging predator
Authors: Street N. E. , Hart P. J. B.
Published: January 2006

The effects of an increase in group size on the location of a concealed food resource by stone‐loach were examined. Food was located more rapidly when group size was increased from one to five individuals. This was achieved by a reduction in the time taken to start searching for food, and by a reduction of travel time. We also found, at group sizes of two and five fish, consistent differences in individual foraging abilities, which were correlated with each fish's patch location performance when alone.
The formation of non‐anadromous populations of Atlantic salmon,Salmon salarL., in Europe
Authors: Berg O. K.
Published: January 2006

Comparison of the different populations of non‐anadromous Atlantic salmon in Europe has revealed some common traits. The non‐anadromous populations probably became isolated from the anadromous salmon populations during a period of rapid land‐upheaval after the last ice age, about 10 000 years ago. The oceanic temperature in the eastern part of the Atlantic was especially low in this period. This probably diminished the advantage gained from the anadromous habit. During this period the low temperatures in the rivers probably increased the frequency of females which matured without migrating seawards. A large number of individuals in the different populations seems to have been favourable for the formation and survival of such races. The occurrence of a lake in such a river system would probably ease the transition to non‐anadromous behaviour, because the salmon would not then be forced to adjust its entire life‐history when isolated (the salmon could spawn in the river in the usual manner and the smolts then migrate downstream into lakes). Larger lakes would also seem to infer problems for the navigation of the smolts towards the outlet. The only known exception is the river‐living land‐locked salmon population found in the River Namsen, Norway.

The factors mentioned above have led to an increase in the probability of occurrence and thriving of mature females without a sea migration or to a decrease in the competitive advantage of anadromous behaviour. The above mentioned similarities can explain the seemingly casual distribution of the non‐anadromous populations of Atlantic salmon in Europe.
Estimation of population parameters and their application to the development of fishery management models in two African rivers
Authors: Payne A. I. , McCarton B.
Published: January 2006

The dynamics of fish populations in two African rivers are being investigated with a view to developing fishery management models for tropical non‐floodplain rivers. Preliminary work was carried out in the Rufiji River, East Africa, to establish growth and mortality rates along with L∞ and K for six species in a river where fishing mortality is zero. These parameters, derived from scale‐reading and length frequency analysis, also allowed the development of phased management plans for the fishery resulting from impoundment.

A subsequent investigation has begun on a West African river, the Taia in Sierra Leone, to pursue observations over four seasons, two of which are now complete. A systematic daily sampling programme is being carried out of the whole community, to accumulate similar but more extensive data to those obtained previously. In the Taia, however, fishing mortality must also be estimated from catch surveys, and analysis is carried out using the recently developed ELEFAN programs which can be compared with results obtained by other methods such as scale‐reading.
Genetic engineering in rainbow trout, Salmo gairdnerii Richardson, by the suppression of meiotic and mitotic metaphase
Authors: Purdom C. E. , Thompson D. , Lou Y. D.
Published: January 2006

Diploid gynogenesis in rainbow trout eggs was induced by a heat shock applied after fertilization with UV irradiated sperm. Survivals were high when the heat treatment was given soon after fertilization at times corresponding to the completion of egg meiosis but were low at all other times. Increases in survival occurred, however, when the heat treatment was given at 4 h 30 min and 5 h after fertilization, with an incubation temperature of 10°C, and at 9 h after fertilization, with an incubation temperature of 5°C. Electrophoretic analysis at three enzyme loci demonstrated a significant increase in homozygous offspring from eggs given these later heat treatments when compared to offspring from eggs treated between 40 and 70 min after fertilization, again with an incubation temperature of 10°C. There was still a significant frequency of heterozygotes in these groups, however, probably of spontaneous origin via diploidization during meiosis. No tetraploid alevins were observed after normal fertilization and attempted suppression of first mitosis.
The effect of temperature and mass on routine oxygen consumption in the South African cyprinid fish Barbus aeneus Burchell
Authors: Eccles D. H.
Published: January 2006

Routine metabolism was measured for Barbus aeneus ranging in mass from 4.1 g to 520 g over the temperature range 9.5–26°C. The mean slope of the double logarithmic relationship between total oxygen consumption and mass was 0.69. The slope of the response of specific oxygen consumption to temperature increased with increasing mass. It is suggested that the lesser effect of temperature on specific oxygen consumption in smaller fish is because osmosis is a passive physical process, with a Q10 in the range 1.1–1.4, while the Q10 for biochemical processes is typically in the range 2–4. At lower temperatures a greater proportion of the total metabolism would therefore be devoted to osmoregulation. This would have implications for the energy balance of small fishes, since in these the ratio surface area: mass is greater and accordingly the proportion of total metabolism devoted to osmoregulation would be higher than in larger individuals.
Pathology associated with Edwardsiella ictaluri in catfish, Ictalurus punctatus Rafinesque, and Danio devario (Hamilton‐Buchanan, 1822)
Authors: Blazer V. S. , Shotts E. B. , Waltman W. D.
Published: January 2006

The pathology associated with infections of Edwardsiella ictaluri in a new host, the danio, is described and compared to that observed in the channel catfish. In catfish the acute stage was characterized by petechial haemorrhage of the jaw, ventral body surface, and at the base of the fins. In chronic cases a characteristic finding was an erosion of skin and muscle overlying the skull, exposing bone and occasionally the brain. Histologically there was a diffuse granulomatous inflammation of the olfactory bulb and the telencephalon. In the catfish the infection was often systemic, involving intestine, liver, spleen, and occasionally kidney. In the danio no gross lesions were observed. Infected fish exhibited an erratic, spinning‐type swimming behaviour. Histologically, lesions usually were confined to the brain. They consisted of an acute, primarily granulocytic inflammation of the medulla oblongata (rhomboencephalon). Only one fish showed evidence of a systemic infection.
Growth rates of Lutjanidae (snappers) in tropical Australian waters
Authors: Edwards R. R. C.
Published: January 2006

Growth rates of three commercial species of Lutjanidae were estimated from sections of vertebrae cross‐checked with scales. The von Bertalanffy growth constants for Lutjanus malabaricus were K=0.168, L∞=70.7 cm standard length (S.L.). For Pristipomoides multidens these were K= 0.219, L∞= 59.1cm, and for Pristipomoides typus K=0.254, L∞= 51.5 cm. Length/weight was analysed in the form W= aLb where W was fresh weight (g) and L= S.L. (cm). The constants were: L. malabaricus, a= 0.041, b= 2.842; P. multidens, a=0.032, b= 2.897; P. typus, a= 0.038, b= 2.822. The growth rates were considered low in comparison with demersal fish counterparts from temperate seas.
The population, survival, growth, reproduction and food of arctic charr,Salvelinus alpinus(L.), in four unexploited lakes in Greenland
Authors: Sparholt H.
Published: January 2006

The material comprised 1205 arctic charr caught by gillnets and electrofishing in the ice‐free season 1982 in four interconnected lakes. The lakes were similar in biotic and abiotic factors and the arctic charr populations were therefore treated as one population. Two size groups of fish older than three years, called ‘small charr’ and ‘large charr’, were found. The two groups differed in feeding habits, growth rates, age of maturity and spawning frequencies. However, they did not differ in the frequencies of the F‐ and S‐ serum esterase alleles, and were in accord with the model proposed by Johnson (1976) which states that the ‘small charr’ and ‘large charr’ are two different forms of the same population. ‘Small charr’ recruit to the ‘large charr’ by entering a period of fast growth. In the investigated lakes this occurred when the ‘small charr’ were 3–10 years old. Some indications of rematuration of the ‘small charr’ when entering the group of ‘large charr’ were found.
The food, feeding habits and feeding structures of the whiting species Sillago sihama (Forsskål) and Sillago analis Whitley from Townsville, North Queensland, Australia
Authors: Gunn J. S. , Milward N. E.
Published: January 2006

The diet, feeding habits and feeding structures of 519 Sillago sihama and 493 S. analis specimens collected from beaches and estuaries in the Townsville region are described. The species are carnivores on a wide range of benthic, epibenthic and planktonic prey. Both undergo size related dietary shifts; S. sihama from predominantly planktonic crustaceans in fish of less than 80 mm t.l. to polychaetes, penaeid and brachyuran crustaceans and molluscs at larger sizes; S. analis from a mixture of small Mesodesma eltanae and amphipods at sizes of less than 80 mm t.l. to predominantly M. eltanae and small quantities of penaeids and brachyuran crabs in larger fish. The dietary shift was not associated with migration from a nursery area.

While the species showed considerable overlap in the types of prey utilized, there were significant differences in the relative importance of shared components in their diets. The major difference was in the relative importance of the bivalve mollusc, M. eltanae. This was the dominant food of S. analis but of secondary importance in S. sihama. Associated with this basic difference in diet was a specialization of the pharyngeal dentition in S. analis to molariform crushing plates and a reduction of the gill rakers to vestigial knobs. In S. sihama, the pharyngeal teeth are sharp and pointed and the gill rakers normal.

The feeding activity of S. analis, but not S. sihama, is limited by the tidal cycle, a factor which may be a form of temporal partitioning.
The food of Atlantic salmon, Salmo salar L., caught by long–line in northern Norwegian waters
Authors: Hansen L. P. , Pethon P.
Published: January 2006

A total of 1145 stomachs from Atlantic salmon caught over the shelf off Helgeland/Trøndelag, and in the oceanic waters off Andenes, northern Norway during late winter–spring, 1969–1972 were examined. Food was found in 52.9% of the stomachs examined. The most important food items found in fish caught in the Helgeland/Trøndelag area were euphausids and hyperid amphipods while the myctophid Benthosema glaciale, the squid Gonatus fabricil and euphausids were found most frequently in the salmon caught off Andenes. Most salmon had preyed upon only one species, and few stomachs contained three or more prey species. The type of food did not appear to be related to the length of the fish. It is suggested that some mesopelagic feeding occurred.
Morphological and meristic differences among spawning aggregations of north‐east Atlantic herring, Clupea harengus L.
Authors: King D. P. F.
Published: January 2006

Univariate and multivariate analyses were performed on seven anatomical characters of Atlantic herring, Clupea harengus, sampled from seven discrete spawning grounds to the west of the British Isles and from spawning sites in the Baltic and Thames Estuary. Analysis of mean similarities, Mahalanobis D2, percentage overlap and projections from prinicipal co‐ordinate analysis demonstrated that a high degree of anatomical similarity exists among the herring spawning communities to the west of the British Isles. Although local aggregations had distinct centres of abundance they appeared to have large overlapping distributions. However, the Celtic Sea sample was found to be distinctly different from adjacent and neighbouring stocks. The samples of coastal herring from the Thames Estuary and the Baltic Sea showed little overlap with other samples.
Changes in structure of tissues and in plasma cortisol during the spawning migration of pink salmon, Oncorhynchus gorbucha (Walbaum)
Authors: Mcbride J. R. , Fagerlund U. H. M. , Dye H. M. , Bagshaw J.
Published: January 2006

Changes in the structure of the gonad, skin, interrenal, liver, kidney, stomach, gill and pituitary gland, as well as blood cortisol and haematocrit values were investigated in adult pink salmon during their migration through the Fraser and Thompson Rivers to the spawning grounds. At the commencement of their freshwater migration the gonads of both males and females were in an advanced state of development, the pituitary contained a large complement of well‐granulated gonadotrops, and hypertrophy was evident in the interrenal tissue and in the epidermis of the skin. At this time, no change from the normal sexually immature salmon was evident in the structure of the gill, liver or stomach. Sclerosis of the glomeruli was noted in the kidney. The plasma cortisol level was consistent with concentrations in unstressed salmon.

Migration of the fish through a turbulent section of the Fraser River evoked a marked increase in both blood cortisol concentration and in interrenal nuclear diameters.

On arrival at the spawning grounds, 10–15 days after entry into fresh water, a general but not marked deterioration of the tissues was evident. The results are discussed in relation to the spawning migration of other species of Pacific salmon.
Effects of aluminium in hard, acid water on metabolic rate, blood gas tensions and ionic status in the rainbow trout
Authors: Malte H.
Published: January 2006

Rainbow trout, Salmo gairdneri, cannulated in the dorsal aorta, were exposed to 2 mgl−1 aluminium (added as Al2(SO4)3, 18H2O) at pH = 5.0 in hard water of very high calcium concentrations (3.3 mmol 1−1). No changes were observed in the concentration of the major plasma ions. The fish, however, became hypoxic, as seen from a fall in the dorsal aortic oxygen tension from around 100 mmHg to 30–40 mmHg, and a simultaneous increase in carbon dioxide tension. Moreover, exposure resulted in a 15% increase in standard oxygen uptake. The ventilation frequency doubled and swelling of the erythrocytes was observed. The results are discussed in the light of some earlier data on the effects of acid/aluminium exposure in water of low calcium concentration, and reveal an important role for calcium in the physiological responses to low pH and aluminium.
The energetics of feeding strikes in larval carp, Cyprinus carpio
Authors: Drost M. R. , van den Boogaart J. G. M.
Published: January 2006

The prey intake of larval carp is described from high‐speed (200–1250 frames s−1) films with synchronous lateral and ventral views. Even in first‐feeding carp larvae, the operculars are functional in sealing effectively the opercular slit until the moment of prey intake, and the maxillaries close off the corners of the mouth, preventing leak flow. In reducing the distance between larva and prey during attack, the relative importance of sucking the prey towards the mouth and swimming forward is variable; overall they are about equally important. The volume and the velocity of the water sucked into the mouth cavity during prey uptake are calculated. The energy costs of suction, i.e., accelerating the water sucked into the mouth cavity, during prey intake are estimated from these values. The energy costs of suction and swimming are in the same order of magnitude. Together they form only a fraction of 1% of the energetic content of the prey, so considerations about energy expenditure seem unimportant in a strategy to optimize the prey attack. During searching, however, they will be important. Power requirements during attack may also be important.
Long‐term tagging of elvers, Anguilla anguilla, with radioactive europium
Authors: Hansen H. J. M. , Fattah A. T. A.
Published: January 2006

Elvers were labelled with 152Eu and 155Eu. Optimum conditions turned out to be incubation for 3 h at 15°C in artificial sea water containing 2% NaCl and 0.1% KCl, EuCl3 at 1 mCi (37 MBq) 1−1 and an eel concentration of about 15%. Laboratory experiments pointed to a biological half‐life of added europium of 1.6–0.5 years. Thirteen hundred 155Eu‐labelled elvers (50 Bq per eel), each weighing on average 0.21 g, were set out near Oskarshamn on the east coast of Sweden in June 1982. Three of these were caught nearby in May 1985 and one was caught in August 1985. They weighed then on average 56 g and showed no significant loss of label other than the physical half‐life (5.1 years). All the radioactivity was found in bone tissue.
Tetracycline tagging in coregonid embryos and larvae
Authors: Dabrowski K. , Tsukamoto K.
Published: January 2006

Coregonus peled (Gmelin) embryos at the eyed stage were immersed in tetracycline hydrochloride (TC) solution (600 mg l−1) and fluorescent marks on the otoliths from fish were identified under a UV light microscope. Three weeks after treatment, when the larval fish had hatched, multiple primordia of the sagitta had fluorescent bands whose locations suggest that calcification begins before formation of the otolith's core. Upon hatching, increments were few or absent, and daily increments started forming after hatching. In coregonid larvae immersed in TC solution immediately after hatching, the fluorescent band was only 1 day's growth increment wide in the otolith. The age of larvae based on ring counts after marking corresponded to the actual age, but further studies are required. Triple marks due to 35‐h immersions in TC solution separated by 5–7 day feeding periods were clearly readable in the otoliths. One month after treatment the fluorescent marks were identified under UV light on otoliths from every fish. In treated embryos, 38% of fish had marks 3 months after TC immersion, whereas in treated larvae 60–80% of fish grown up to 38.7 mm were marked.
Serum pigmentation in Cyclopterus lumpus L
Authors: Mudge S. M. , Davenport J.
Published: January 2006

Female lumpsuckers, Cyclopterus lumpus L., have blue‐green blood serum and subcutaneous gelatinous tissue; the male's are red/magenta in colour. The female serum contains a chromoprotein with biliverdin as the prosthetic group; the male serum contains the same biliverdin pigment but this is normally masked by a red pigment, probably phycoerythrin. The female serum also contains the red pigment but at a much lower concentration than in the male. These bile pigments are probably formed by the breakdown of haem in the liver. Lumpsucker gall bladders are relatively small and do not enlarge during starvation. Storage of bile pigments in the serum and subcutaneous jelly may have arisen in response to the problems of regular long‐term starvation. The pigments now appear to have an additional sexual signalling function.
Alterations to the swimming performance of carp, Cyprinus carpio, as a result of temperature acclimation
Authors: Heap S. P. , Goldspink G.
Published: January 2006

Groups of common carp were acclimated to either 10°C or 28°C for 6 weeks. Fish were then exercised at 10°C or 20°C, and the critical swimming speed (fatigue velocity) was measured. At 10°C, cold‐acclimated carp were capable of significantly higher swimming speeds. When exercised at 20°C. however, the situation was reversed, and warm‐acclimated carp exhibited improved swimming ability. These results provide direct evidence that acclimation of the contractile proteins is beneficial across a wide temperature range. Following acclimation to low environmental temperatures the critical swimming speed exhibited a Q10 of only 1.1 for the temperature range 10–20°C. compared to a value of 2.9 for fish acclimated to the higher temperature.
Size‐segregative behaviour in minnow shoals
Authors: Pitcher T. J. , Magurran A. E. , Allan J. R.
Published: January 2006

Shoals composed of equal numbers of two size‐classes of European minnows were observed undisturbed, feeding and after threat from a pike in a large arena tank.

The time/frequency budget and analysed sequences of behaviour of the two size‐classes were very similar. Irrespective of size, for standard behaviour measures, fish in the shoal behaved similarly under the same external influences, including predator threat.

In contrast, however, the distribution of the two size‐classes provided evidence of size segregation within the shoal. This was brought about by individual minnows making shoaling responses preferentially to their own size‐class. After exposure to the predator, shoaling responses changed and differed between small and large minnows.

The outcomes of contests at foraging patches were governed primarily by fish size and information asymmetry rather than by occupation of a feeding site.

The experiment shows that asymmetrical pay‐offs in foraging and in response to predator threat are the probable reasons for size‐segregation behaviours. This conclusion supports the views of earlier workers that mechanical sorting by swimming speed is not an important factor in size segregation in shoals.
On causation and function of the pre‐spawning behaviour of cichlid fish
Authors: Baerends G. P.
Published: January 2006

This paper reviews studies based on the theory that animal behaviour is organized and controlled by a taxon‐specific ‘software’ design, to which the principles valid for the evolution of morphological and physiological mechanisms equally apply, and which therefore is also subject to adaptive radiation.

Causal ethological analysis of the pre‐spawning behaviour of some oral‐ and some substrate‐breeding cichlid species has led to the conclusion that the course of this behaviour, as well as the character of its elements, results from the interaction of at least three mutually‐incompatible behavioural control systems serving, respectively, escape from danger, repulsion of conspecifics (‘aggression’), and attraction of a mate (‘sex’). In the course of pre‐spawning behaviour, the third system gradually gains control over the other two, at least with respect to a particular individual (i.e., the potential mate), losing its effectiveness as a releasing stimulus for aggression and/or escape the more an affinitive individual relationship is built up.

In all cichlids, specific motor patterns resulting from the interaction of different sytems in the behavioural organization are functional in selection of the sex‐partner and in preparation of the spawning site. In the sexually dimorphic oral incubators, the form of these activities also differs between the sexes. Performed alternately by male and female, they form a stimulus‐response chain. In contrast, in the monomorphic substrate spawners, in which pair bonds last much longer, these activities are the same in both sexes, which usually perform them simultaneously. In addition to the two functions just mentioned, they serve the establishment of the long‐lasting bond between partners, and the necessary synchronization of their endocrine states for spawning.
Mate choice and size assortative pairing by the cichlid fishes of Lake Jiloá, Nicaragua
Authors: McKaye K. R.
Published: January 2006

Size‐assortative mating occurs for all six substratum‐spawning cichlids studied in Lake Jiloá, Nicaragua. Mate quality is clearly a dominant consideration for both sexes, as larger pairs had disproportionately more young surviving beyond 3 weeks. Mating with the largest available mate should generally be advantageous to both sexes, since the success of a pair is dependent on their ability to take and defend a territory. A model involving mate discrimination by both partners is developed and contrasted to models involving single sex discrimination with intrasexual competition.
Effects of varying discharge on the downstream movement of salmon fry, Oncorhynchus tshawytscha Walbaum
Authors: Irvine J. R.
Published: January 2006

Some of the consequences of varying flows on the downstream migration of salmon fry were investigated in five replicate streams adjacent to the lower Waitaki River, New Zealand. Fluctuating discharge appeared to increase the number of fry moving downstream, provided that mean water velocities at peak flows exceeded 25 cms−1’and that some fry were migrating out of the streams anyway. Salmonids appear to have a lengthier flow–sensitive period than has been proposed in the literature. Research is required to determine whether recently emerged fry that leave parental spawning streams in New Zealand disperse immediately to the ocean or develop and grow for extended periods en route. It may sometimes be feasible and worthwhile to minimize stream flow variations to encourage fry to remain longer in fresh water.
Spawning performance in North American minnows: direct evidence of the occurrence of multiple clutches in the genus Notropis
Authors: Heins D. C. , Rabito F. G.
Published: January 2006

Pairs of laboratory–reared F1, and F2 males and females of Notropis leedsi were observed in aquaria. Analyses of spawning histories and ovum diameter histograms showing the pattern of ovum development demonstrated that females produced multiple clutches of eggs. Each clutch is comprised of oocytes which undergo synchronous development and are oviposited within a relatively short period of time. Examinations of collections from streams in Florida and Georgia showed that N. leedsi has a spawning season which lasts at least from May to September. Because the pattern of ovum development in wild‐caught females was the same as that observed in laboratory females, we believe that our laboratory observations demonstrate processes which occur in the natural environment. A total of 193 spawning intervals was observed in 34 pairs kept at 22–26°C in the laboratory. The interspawning intervals ranged from 3 to 10 days, with a mean of 4.6 days and a mode of 4 days. The clutches ranged in size from 26 to 28 ova for females of 36.7–52.5 mm standard length.
Histochemical characterization of myotomal muscle in the grass pickerel, Esox americanus vermiculatus (LeSeuer), and the muskellunge, E. masquinongy (Mitchell)
Authors: Hoyle J. , Gill H. S. , Weatherley A. H.
Published: January 2006

A histochemical study of the myotomal muscles in the grass pickerel, Esox americanus vermiculatus, and the muskellunge, E. masquinongy, was performed using actomyosin ATPase and NADH diaphorase activities. Three fibre types, i.e., red, white and pink were distinguished on the basis of their enzyme activities. White muscle fibres comprised the bulk of the myotomal musculature. The relative proportion of red muscle fibres was greater in the caudal region than in more anterior regions of the body. Pink fibres formed only a few layers between red and white. These findings are discussed in relation to the possible functional significance of the muscle fibre types in swimming and feeding behaviour in these species.
Transmission electron microscope observations of C‐banded skipjack tuna chromosomes
Authors: Song Y. C. , Ratty F. J. , Laurs R. M.
Published: January 2006

C‐banded mitotic chromosomes of Katsuwonus pelamis (Linnaeus) were examined by transmission electron microscope (TEM) and results compared with light microscopy images. Advantages of the TEM technique are noted.
Blood and other possible inflammatory cells in the sparid Acanthopagrus australis (Günther)
Authors: Roubal Frank R.
Published: January 2006

The peripheral blood cells of Acanthopagrus australis include erythrocytes, elongated and rounded thrombocytes, lymphocytes, neutrophils and monocytes. The ultrastructure of lymphocytes, neutrophils and monocytes is described. Type 1 cells with characteristic elongated, eosinophilic granules and type 2 cells with rounded, apparently labile granules are common in the gill filaments and do not increase or decrease significantly in abundance in ectoparasite‐infested gill filaments. Extravascular neutrophils tend to be more evident in pathologic tissue. Lymphocytes and the macrophage‐like type 3 cells are the most abundant infiltrating cells in pathologic gill tissue. Apart from ultrastructural and histochemical data, granule length and width are sufficient criteria to distinguish between the neutrophil, type 1, type 2 and type 3 cells.
The variability in catches from multi‐mesh gillnets fished in three Canadian lakes
Authors: Craig J. F. , Sharma A. , Smile K.
Published: January 2006

Three types of multi‐mesh gillnet were fished in three lakes in Alberta during spring and summer of 1983. Eight species offish were caught in a total of 89 lifts. The variability of the catches was analysed after a transformation into y= log (x+1). For the major species (apart from yellow perch) there were remarkable similarities between species for error variances associated with catches from nets and from meshes. The total error variance associated with a catch from any net was 0‐0575 (C.V. = 59‐7%). Total error variance associated with a catch from a single mesh was 0‐0852 (C.V. = 75‐6%). These values are compared to those from other studies and an error variance estimate of 0‐0868 (C.V. = 76‐5%) was considered to be an appropriate value for gillnet catches in fresh waters. In sampling programmes more than six nets would need to be used for confidence limits to be below half or more than twice the geometric mean.
Estimates of catch and potential yield for the riverine artisanal fishery in The Gambia, West Africa
Authors: Lesack L. F. W.
Published: January 2006

The limnological characteristics of the Gambia River have resulted in a seasonally dynamic fish composition and a complicated artisanal fishery. The estimate of catch (2700t year−1) for the fishery during 1980 is low compared to potential yield as predicted by empirical relations with river channel length, drainage basin area, floodplain area, and the morphoedaphic index. A decrease in catch per unit effort was weakly correlated to increasing effort during March‐July in the lower river. For the overall Gambian fishery, however, temporal changes in catch per unit effort were not correlated with changes in effort. Predictions of yield are consistently higher than catch estimates for the fishery and suggest underexploitation of the stocks. Many assumptions of the predicting techniques, however, are unsatisfied, and the year‐to‐year variability of the Gambia River catch is unknown. Consensus seems to emerge if only crude evaluations of a fishery are needed, but the predicting techniques do not provide the degree of resolution required for most management decisions.
Feeding relationships of a demersal fish assemblage on the west coast of Scotland
Authors: Gibson R. N. , Ezzi I. A.
Published: January 2006

The feeding relationships of an assemblage of demersal fishes present on a soft‐sediment bottom off the west coast of Scotland in the late summer‐autumn were investigated. On the basis of stomach content analyses of the fifteen commonest species, three major feeding types could be distinguished. The first consisted of small browsing species feeding predominantly on infaunal polychaetes. The second relied heavily on caridean decapods, but within this group three subgroups could be detected which supplemented their diet with amphipods, mysids or polychaetes, respectively. The third group fed on large prey consisting of mysids and/or fish. Several species passed from one group to another as they grew, and there was a general tendency for fish to become more specialized in their diet with increasing size. The three groups represent a series in which decreasing reliance is placed on the substratum as a source of food.
Observations on movements of yellow eels,Anguilla anguillaL., after displacement from coastal waters to sea
Authors: Rossi R. , Bianchini M. , Carrieri A. , Franzoi P.
Published: January 2006

Four groups of yellow eels, three from three Po Delta brackish bays (Pila, Scardovari and Goro) and one from the French Atlantic coast, were marked by freeze‐branding and released at an open‐sea point 5 miles offshore. Of the 2137 eels released, 453 (21.2%) were recaptured over a 1‐month period. The percentage recaptured is not independent of either fish size (the larger eels being recaptured in greater quantity than the smaller ones which are supposed to be less catchable and more easily overlooked by fishermen) or fish origin (the recapture rate of the French stock was both the lowest, at 9.8%, and the most dispersed in time and space). The highest multiple catches were for eels from Pila and Scardovari and were made in the first days of the experiment. Of the recaptured eels, 75% were caught in the inland water closest (9 km) to the release point; only 8.6% were recaptured at the mouth of the two branches of the River Po. There is no evidence of a real homing tendency for yellow eels previously adapted to living in brackish water: the massive return to the nearest coast is probably only an avoidance reaction to the unfavourable open‐sea environment.
A study of the helminth parasites ofAnarhichas lupus(Perciformes: Anarhichadidae) in the North Atlantic
Authors: Bray R. A.
Published: January 2006

The North Atlantic wolffish,Anarhichas lupus, has a broad, relatively short gastro‐intestinal tract (0.55–1.05 of body length). The stomach‐like region has a high pH, suggesting a functionally stomachless condition. The ‘stomach’ is rarely parasitized by helminths. The gut pH tends to rise along its length as does the concentration of the ion Mg2+, while osmolarity and the ions Na+, Cl−and K+tend to decrease and Ca2+stays practically the same. The intestinal wall is deeply folded, particularly in the anterior region. The intestine commonly harbours several helminth species. The gall bladder and urinary bladder tend to be voluminous and both are commonly parasitized by digeneans.A. lupushas been recorded as harbouring over 30 species of parasitic helminth of which 10 are commonly found, often in large numbers. There is little overlap of parasite sites and there appear to be several empty niches. The parasites tend to fall into three categories, those stenoxenic to this genus of fish, those stenoxenic to other groups and accidental inA. lupus, and those forms which are euryxenic.
Gonadal morphology, enzyme histochemistry and plasma steroid levels during the annual reproductive cycle of male and female brown bullhead catfish, Ictalurus nebulosus Lesueur
Authors: Rosenblum P. M. , Pudney J. , Callard I. P.
Published: January 2006

The annual reproductive cycle of the brown bullhead catfish, Ictalurus nebulosus Lesueur, was investigated over a two‐year period. In females, GSI increased in the spring as follicles enlarged and the granulosa became hypertrophied, dropped during spawning in August, then rose in the autumn as follicles enlarged slightly. 3β‐Hydroxysteroid dehydrogenase (3β‐HSD) activity was limited to thecal nests of large, vitellogenic follicles. Plasma testosterone and estradiol‐17β levels increased in parallel with GSI. Levels of both steroids dropped prior to the spawning period, although a peak in estradiol‐17β was evident during the spawning period. No 11‐ketotestosterone was detected in female plasma. In males, GSI increased in the spring as spermatogenesis proceeded, and dropped during spawning. 3β‐HSD activity was confined to Leydig cells and was most intense prior to spawning. Plasma testosterone and 11‐ketotestosterone peaked during the pre‐spawning period, dropped prior to spawning, then rose slowly during the autumn. A peak in estradiol‐17β occurred during the spawning period. Significant differences in GSI and plasma steroid levels during the pre‐spawning and spawning periods were observed between the two yearly cycles; they may be related to differences in rainfall during these periods.
Long‐term stability in the population levels of the eyefluke Tylodelphys podicipina (Digenea: Diplostomatidae) in perch
Authors: Kennedy C. R.
Published: January 2006

Annual changes in the population size of the metacercariae of Tylodelphys podicipina in the eyes of perch in a small eutrophic lake were studied over ten years by following changes in prevalence, abundance and overdispersion of parasites throughout the life of each year class of fish. The population increased rapidly in the first two years after its introduction to the lake, but for the next six years fluctuated within very narrowly constrained limits before declining as a result of a catastrophic decline in the perch population. No evidence of parasite‐induced host mortality was found: the decline in parasite abundance throughout the life of each year class was due to density‐independent parasite mortality within the fish as a result of natural variation in the life span of the metacercariae. Levels of infection in the first year of a year class were determined principally by transmission processes, as transmission could only occur over a very brief period when release of cercariae from parent generation snails coincided with the presence of perch fry. Transmission appeared to be density‐independent, and infection levels in perch to be determined by the dimensions of the transmission’ window’ and subsequently modified by parasite mortality. No evidence of host responses or any other regulatory factor of fish origin was found, and the infrapopulations in perch appear to be non‐equilibrial and unstable. Although the possibility of regulatory processes acting on infrapopulations of the parasite in other hosts remains, the importance of transmission windows in determining infrapopulation levels in fish is emphasized.
Prey preferences of a riverine population of juvenile chinook salmon, Oncorhynchus tshawytscha
Authors: Sagar P. M. , Glova G. J.
Published: January 2006

The diet of juvenile chinook salmon and the foods available to them were studied during spring and summer in a large, braided, New Zealand river. During both sampling periods fish and potential prey were collected at dawn and dusk. Analysis showed that in spring the feeding rate increased at dawn, when aquatic taxa comprised the majority of their prey. Prey of terrestrial origin dominated the diet at dusk in summer but formed only about 1% of the diet during spring, when few such prey were available.

During spring the fish selectively preyed upon larger nymphs of the mayflies Deleatidium spp. However, in summer chironomids, other dipterans, and trichopterans were consumed to the exclusion of Deleatidium. Most of the chironomids and trichopterans taken were pupae or emerging adults and it is suggested that this may reflect differences in vulnerability during the diurnal emergence period.
Temperature‐dependence of cardiac output and regional blood flow in rainbow trout, Salmo gairdneri Richardson
Authors: Barron M. G. , Tarr B. D. , Hayton W. L.
Published: January 2006

Cardiac output, blood flow distribution and regional perfusion were determined in free‐swimming rainbow trout acclimated to 6, 12 and 18°C, using the indicator dilution and microsphere methods. Cardiac output (ml min−1 kg−1) increased linearly with increasing temperature, while circulation time decreased. Blood flow distribution (% of cardiac output) to the spleen, liver, kidney, gall bladder and gastro‐intestinal tract was significantly reduced at 18°C relative to 6°C‐acclimated fish. White muscle received the largest fraction of cardiac output, and blood flow distribution to white muscle increased significantly with increasing acclimation temperature. Blood perfusion (ml h−1 g−1) of various organs and red muscle was not influenced by acclimation temperature, while white muscle perfusion increased with increasing temperature. These results demonstrate physiological adaptation of the cardiovascular system of rainbow trout to changes in acclimation temperature.
Impact of acidification and eutrophication on the distribution of fish species in shallow and lentic soft waters of The Netherlands: an historical perspective
Authors: Leuven R. S. E. W. , Oyen F. G. F.
Published: January 2006

The species richness and composition of fish assemblages were examined in lentic soft waters in The Netherlands. The selected bodies of water reflected a large variation in geomorphological and limnological factors. In total, 24 fish species were encountered in Dutch soft waters. During 1983–1984 Esox lucius, Perca fluviatilis, Rutilus rutilus, Scardinius erythrophthalmus, Tinca tinca and Umbra pygmaea were quite common. In slightly acid and alkaline waters (pH≥5) Rutilus rutilus, Scardinius erythrophthalmus, Perca fluviatilis, Ictalurus nebulosus and Cyprinus carpio accounted for about 90% of the total number of specimens in the catches. Strongly acid waters (pH < 5) generally were fishless. If fish were present in these waters, however, the catches mainly consisted of Umbra pygmaea. Only in a few strongly acid systems were other species collected. The lowest pH at which certain fish species occurred varied from 3.1 to 7.0. In particular, Umbra pygmaea was extremely acid‐tolerant. The percentage of waters which harboured fish as well as the average number offish species per water decreased steeply between pH 6 and 4.

The sampled waters showed remarkable differences in their fish assemblages. With hierarchical classification, six groups of waters could be distinquished with respect to their fish fauna. The site groups are defined and characterized physico‐chemically and their fish assemblages described. Multivariate analysis showed that the structure of fish communities is strongly related to the pH, the alkalinity, trophic level and the ionic composition of the water. Comparison of historical and recent data on the occurrence of fish strongly indicated that in many sampling sites fish species or even entire fish assemblages had disappeared. Ordination of available data also illustrated recent changes in community structure. At least 67% of the nowadays extremely acid waters formerly harboured fish populations. The impoverishment of fish communities or the total loss of fish were primarily caused by cultural acidification. Limited nutrient enrichment of soft waters only resulted in minor alterations of fish assemblages.
Effect of early aflatoxin B1 exposure on in vivo and in vitro antibody responses in rainbow trout, Salmo gairdneri
Authors: Arkoosh M. R. , Kaattari S. L.
Published: January 2006

Exposure of rainbow trout, Salmo gairdneri, to the carcinogenic mycotoxin, aflatoxin B1, resulted in a loss of B cell memory, but produced no change in the primary B cell antibody response. This effect was demonstrated both in vivo, in the generation of serum antibodies, and in vitro, in the generation of antibody‐producing cells.
Immunostimulation of antibody‐producing cells and humoral antibody to fish bacterins by a biological response modifier
Authors: Kitao T. , Yoshida T. , Anderson D. P. , Dixon O. W. , Blanch A.
Published: January 2006

Numbers of splenic antibody‐producing cells and humoral antibody titres were elevated during immunization regimes in rainbow trout when the bacterins Yersinia ruckeri or Aeromonas salmonicida O‐antigen preparations were mixed with the immunostimulator FK‐565. Fish sampled 14 days after injection showed a marked increase in the immune response when doses of 5, 10 or 100 μg of antigen were used. The immunostimulator may aid initial antigen uptake and processing.
Biometrics of Sardinella longiceps Val. in relation to upwelling in the Gulf of Aden
Authors: Edwards R. R. C. , Shaher S.
Published: January 2006

Growth, size composition, condition factor and gonad index of the oil sardine, Sardinella longiceps Val., oscillated over an annual cycle in relation to upwelling. Growth in length was modelled using the formula of Pauly & Gaschütz (1979):

image

where Lt= length cm at age t years, L∞= 23.8cm, K=0.97, to=0.70, C=1.08 and ts=−0.08. The relationship of growth rate, spawning, and condition factor, to upwelling and plankton blooms is discussed.
The properties of tilapia sperm and its cryopreservation*
Authors: Chao Nai‐Hsien , Chao Wei‐Chung , Liu Kuo‐Chun , Liao I‐Chiu
Published: January 2006

The specific differences between the testis, milt and sperm of six species of tilapia including Oreochromis aureus, O. mossambicus, O. niloticus, Tilapia zillii, O. nilolicus×O. aureus hybrid and red tilapia, Oreochromis sp., were studied. The shape of testis is tubular; the gonadosomatic index varied from 0.07 to 2.71. The pH values of individual milts ranged from 6.2 to 8.2 and the osmolarity from 240 to 380 mOsmol kg−1. The quantity of milt obtained by stripping averaged only about 0.3 ml, and only in the O. niloticus×O. aureus hybrid did it exceed 3 ml. Sperm motility graded from weak to moderate was determined for the stripped tilapia milt. Sperm concentrations ranged from 7.70 × 108 sperms ml−1 in T. zillii to 2.74 × 1010 sperms ml−1 in O. mossambicus. Tilapia sperm was active in various salinity ranges such as 0–5‰ for O. niloticus, and 0–15‰ for O. mossambicus and T. zillii. Extender containing 15% milk and 5% methanol was used to prepare milt mixture before cooling rapidly to −35° C and then at 5° C min−1 to −75° C for storage in liquid nitrogen (– 196° C).

Fertility tests on frozen tilapia milt resulted in a fertilization rate of 72.7% (v. control 85.7%) for the 22‐day frozen milt of the O. nilolicus×O. aureus hybrid used to fertilize the eggs of O. honorum, and 93.4% (v. control 90%) for the 304‐day frozen sperm of red tilapia used to fertilize eggs of red tilapia.
Aspects of the reproductive biology of the grouper, Epinephelus tauvina (Forskål), in Kuwaiti waters
Authors: Abu‐Hakima R.
Published: January 2006

Gonad maturation in Epinephelus tauvina is examined over one annual reproductive cycle. The species has one major spawning period from April to May and this is associated with increasing water temperatures and relatively low salinity. The histological changes in the gonads in the female, male and transitional phase are examined, and oogenesis and spermatogenesis are described in five developmental stages. That E. tauvina is a protogynous hermaphrodite is confirmed, and sexual transition is found to occur in individuals 55–75 cm in length, and is related to spawning activity. Fecundity estimates for E. tauvina of length 35.1–62.3 cm ranged from 850 186 to 2 904 921.