bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of some environmental variables on the ascorbic acid status of mullet, Mugil cephalus L., tissues. I. Effect of salinity, capture‐stress, and temperature
Authors: Thomas P.
Published: January 2006

The effects of capture stress, exposure to a hypo‐osmotic environment and elevated water temperatures on the ascorbic acid (AsA) content of several mullet, Mugil cephalus, tissues were examined. All the treatments significantly altered tissue AsA levels, but the pattern of AsA fluctuations varied. Gill AsA concentrations increased two fold after exposure to a hypo‐osmotic medium (salinity changed from 30‰ to 5‰), whereas AsA content in this tissue declined after capture. Both treatments depleted AsA reserves in the kidney. AsA concentrations in the brain increased after exposure to low salinity and elevated water temperatures, but were unaffected by capture stress. None of the treatments caused long term alteration of hepatic AsA reserves. Ascorbic acid inhibited oubain‐sensitive Na+, K+‐ATPase activity of gill tissue in vitro. The results suggest an involvement of AsA in osmo‐ or ion‐regulatory functions of teleosts gills, salinity and thermal adaptation mechanisms in neural tissue, and the response of renal tissue to adverse environmental stimuli.
Fish production in Oued Sebaou, a seasonal river in North Algeria
Authors: Penczak T. , Moliński M.
Published: January 2006

Fish were sampled by electrofishing at three contiguous sites 26 km from the source of Oued Sebaou, a seasonal river in North Algeria. River discharge ranges from 300 m3s−1 in the peak of the rainy season to 0.1 m3s−1 at the end of the dry season. Extensive gravel extraction from the river bed takes place during the dry season.

Two species were recorded at each site: Barbus callensis, which is heavily fished locally, and Anguilla anguilla. The three sample maximum likelihood Zippin method was used to estimate mean density and standing crops, which were: barbel, 452 fish ha−1, 5.33 kg ha−1; eels, 149 fish ha−1, 3.04 kg ha−1. Estimated average biomass and production were: barbel, 2.31 kg ha−1, 4.27 kg ha−1 year−1; eels, 1.51 kg ha−1, 2.60 kg ha−1 year−1.
Acclimation of rainbow trout, Salmo gairdneri Richardson, to zinc: kinetics and mechanism of enhanced tolerance induction
Authors: Bradley R. W. , DuQuesnay C. , Sprague J. B.
Published: January 2006

Pre‐exposure of rainbow trout to 0.31–0.53 of the lethal concentration of zinc increased their tolerance of the metal by a factor of 2.5. This acclimation was fully induced within 5 days, and completely lost within 7 days when fish were returned to zinc‐free water. The changes in tolerance were closely paralleled by changes, in both liver and gill tissue, of heat‐stable, sulfhydryl‐rich protein (an estimate of levels of metal lothionein, MT). This strongly suggests that MT is involved in the induction of enhanced tolerance of zinc. Zinc residues in liver and gill tissue did not parallel the changes in MT levels and tolerance. Thus MT does not appear to bind and store excess zinc; however, it may increase the ability of acclimated fish to regulate the levels of zinc in their gills. This hypothesis is supported by the observation that the rate of accumulation of zinc in gill tissue was slower in acclimated fish than in control fish.
The effect of the migration of Alosa fallax fallax (Laécpède) into fresh water, on branchial and gut parasites
Authors: Aprahamian Miran W.
Published: January 2006

The prevalence and relative density of branchial and gut parasites taken from Almafullax in the estuary of the River Severn, at the start of the freshwater phase of its spawning migration, were compared with those taken from their spawning grounds in fresh water. Mazocrues alosue showed no significant difference in prevalence between the two habitats, though their relative density did fall significantly. Because of the direct relationship between length and relative density, this difference may be explained by the estuary samples of A. fullux being of fish significantly larger than those from fresh water. Other possible causes are discussed. The prevalence and relative density of M. alosae showed a trend to increase with age of the host. Repeat spawning A. fallax had a significantly greater relative density and prevalence of M. alosue when compared to virgin fish.

Analysis of the sampled population showed that Clavellisu emarginata declined significantly in both prevalence and relative density in fresh water, and this was confined to the younger and first time spawning A. fullux. Thynnuscuris aduncum showed significant reductions in prevalence and relative density of infection in fresh water when compared to the estuarine samples.

The species Hemiurus uppendiculatus and Pomphorhynchus laevis showed no significant difference in prevalence and relative density of infection, and Pronoprymna ventrzcosa no significant difference in prevalence, between the two habitats.
The relationship between growth, food conversion and oxygen consumption in developed and underdeveloped American eels, Anguilla rostrata Lesueur
Authors: Degani G. , Lee‐Gallagher M.
Published: January 2006

This study examined the influence of body size and temperature on oxygen consumption and food converstion in juvenile American eels (Anguilla rostrata). The weight‐specific oxygen consumption rate for underdeveloped eels (18 months old) was significantly higher than the weight‐specific oxygen consumption rate of developed eels of the same weight (6 months old). Oxygen consumption rates increased linearly with weight at each experimental temperature (15, 20, 25°C) when data were transformed logarithmically. No significant differences were found among slopes oflog transformed data at varying temperatures. Oxygen consumption was significantly higher at night (2300 h) as compared to morning (0900 h). The results indicate that underdeveloped eels use more energy and use less food less efficiently than developed eels.
Mortality of pre‐smolt Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., caused by fluctuating water levels in the regulated River Nidelva, central Norway
Authors: Hvidsten N. A.
Published: January 2006

The river Nidelva, situated in central Norway, is regulated for production of electricity. Water discharge may vary from 150 to 30 m3 s‐1 over a period of 10 min at the outlet of the power stations. The water level then sinks 50 cm during the next 30 min. The Nidelva produces both salmon and trout. Water fluctuations were found responsible for large losses of O+ salmon and trout. The recruitment of salmon was concluded as satisfactory, while recruitment of trout was reduced as a result of stranding.
Homeostatic regulation of acetazolamide‐sensitive esterase activity in the bluegill sunfish, Lepomis macrochirus, following acute cold shock
Authors: Larrick S. R. , Cherry D. S. , Cairns J.
Published: January 2006

Acetazolamide‐sensitive esterase activity was elevated in branchial homogenates of control juvenile bluegill sunfish, Lepomis macrochirus, acclimated at 20° C but decreased rapidly within 9 h following an acute hypothermal shock to 8° C. After 2 weeks at 8° C, shocked‐fish enzyme activity was similar to control fish. At 20° C acclimation temperature, specific activity of bluegills was similar in swimbladder, liver, kidney, gill, spleen, and gonad homogenates and was significantly higher (α=0.05 level) in whole blood homogenates. The pH optima for enzymes extracted from fish acclimated at 20° and 8° C were 7.29 and 8.00, respectively. Polyacrylamide gel electrophoresis (PAGE) demonstrated two distinct forms of acetazolamide‐sensitive esterase activity present in both 20° and 8° C acclimated fish. Specific activity for homogenates from both 20° and 8° C acclimated fish differed significantly when assayed at 20° C, suggesting both qualitative and quantitative changes in acetazolamide‐sensitive esterase. It is postulated that relatively rapid alterations in esterase activity promote survival in bluegill following acute cold shock through the central role of enzymes in the regulation of plasma ion concentrations and acid/base equilibria.
Reappraisal of nuclear DNA content of rodlet cells compared to several cell types from some freshwater teleosts, using two methods of microdensitometry
Authors: Barber D. L. , Westermann J. E. Mills
Published: January 2006

Nuclear DNA contents of rodlet cells from Catostomus commersoni, Semotilus atromaculatus and Cyprinus carpio were compared with nuclear DNA of erythrocytes and larger cells of the same species, using scanning microdensitometry and averaging microdensitometry. This study reappraises the work of Barber & Westermann (1983), which employed averaging microdensitometry only, and compared rodlet cell nuclear DNA only with erythrocyte DNA. In addition, this work considers sources of error in both methods of microdensitometry, and comments upon the use of microdensitometry of either method as a mechanism for making distinctions among the DNA contents of cells of different types. The results of the present work consistently indiate no significant differences within species between nuclear DNA content of rodlet cells and larger teleost cells, using either method of microdensitometry. Because of the lack of statistically significant difference in DNA content between nuclei of rodlet cells and those of known teleost cells, it has been concluded that the rodlet cell itself is probably of teleost origin. However, the method indicates nothing about the origin of the rodlets, which have also been shown to contain DNA, but are Feulgen‐negative.
Habitat evaluation as a fisheries management tool
Authors: Milner N. J. , Hemsworth R. J. , Jones B. E.
Published: January 2006

The application, rationale and process of habitat evaluation methods are discussed in the context of present day fisheries management. The need to consider habitat features at site and catchment level is stressed.

Development of habitat evaluation techniques for assessing brown trout habitat in Welsh streams is reported, and examples of these approaches are given: qualitative (visual assessment), semi‐quantitative (a combination of subjective and quantitative measurements) and quantitative (measurements on transect system). Habitat attribute‐fish population models were based on functional linear regressions and multiple regression (for the quantitative method). Quantitative models explained up to 80% of the variance in abundance of medium sized (10–20 cm) trout in hard water (>25mgl‐1 CaCO3), but were less effective when data from soft waters were included. Testing of the qualitative and semi‐quantitative methods on independent data demonstrated that the latter was more effective in predicting habitat quality.

Survey costs varied considerably but, although the more precise methods were more costly per site, they were the most cost‐effective because fewer sites were required for a given level of precision.

The problems associated with soft‐water sites are discussed in terms of factors affecting site carrying capacity; and selection of methods is briefly considered in the light of current management practise.
The effects of the Kielder scheme on fisheries
Authors: Cave J. D.
Published: January 2006

The scheme is briefly described. The success of the Kielder and Bakethin reservoir fisheries is examined. The poor condition of trout in Kielder reservoir is considered in relation to physical and chemical factors including water turbidity, low nutrient levels and the location of the reservoirs.

The performance of Kielder hatchery and the difficulties of collecting broodstock of Tyne origin are described.

The effects of water releases from Kielder reservoir upon the salmon, Salmo salar L., and brown trout Salmo trutta L., fisheries within the River North Tyne and examined. Aspects considered include modified water temperature regimes, water chemistry and the magnitude and timing of releases for river regulation and generation of hydroelectric power.

The problems associated with fish passage at Riding Mill weir, the point of water transfer to the River Wear and River Tees, are examined and the progress of inter‐river transfers is described.
Sampling strategy related to fish distribution, with particular reference to the Norfolk Broads
Authors: Jordan D. R. , Wortley J. S.
Published: January 2006

Large‐scale movements of fish within a complex freshwater system such as the Norfolk Broads can give rise to erroneous sampling data if the extent of these movements is not fully appreciated. The Norfolk Broads habitat is briefly described, and data are presented showing that mean estimates of standing crop in the broads vary from <1gm‐2 in the winter to 9.4 gm‐2 in the summer. The widespread nature of the phenomenon is demonstrated by winter and summer data from five broads, and a more detailed picture of the seasonal changes is shown by an intensive 2‐year study on one of these broads. Winter aggregations of fish have been found in sites adjacent to rivers connected with the broads, with densities of up to 36.7 fish m‐2 and a biomass of 1787 gm‐2. Accurate overall estimates of fish standing crop can only be obtained when fish are maximally dispersed during the summer months.
An alternative concept to home range theory with respect to populations of cyprinids in major river systems
Authors: Linfield R. S. J.
Published: January 2006

Homing behaviour in cyprinid species has been demonstrated by a number of research workers during the past 35 years. The British work has been principally conducted through tank experimentation with roach, gudgeon and minnows, but limited field data indicating home range behaviour have also been published. Evidence is now presented, from a fish population assessment and management programme covering 6000 km of river fisheries in the Anglian region of eastern England, to suggest that home range mechanisms do not play a significant role in the overall stock dynamics of cyprinid species in major river systems.

An alternative hypothesis which fits the range of observed circumstances more closely is described, based on a perception of cyprinid communities as totally mobile populations influenced predominantly by river flow characteristics and behavioural responses to flow and seasonal temperature factors. This concept is illustrated with a sequential series of schematic diagrams of a river catchment in which the key factor of infinitely variable movement patterns interspersed with periods of passive downstream displacement (negatively size‐related) is modified by increasing degrees of interference by river structures.

The implications of the alternative concept to the management of riverine fish populations is discussed and alternative strategies to the traditional style cyprinid stockings illustrated within the paper are suggested which do not rely on home range mechanisms.
Effects of pollutants in fresh waters on European non‐salmonid fish I: Non‐metals
Authors: Solbé J. F. de L. G. , Cooper V. A. , Willis C. A. , Mallett M. J.
Published: January 2006

As part of a programme of acquiring data for preparing standards to safeguard European, nonsalmonid, freshwater fish from pollution, toxicity tests were carried out in hard, well‐aerated water. Asymptotic median lethal concentrations (LC50s) of undissociated ammonia, cyanide, nitrite and phenol to one or more of three species were determined. The LC50s were as follows: to common carp 16mg1‐1 as NO2–N; to perch 0.1 mg1‐1 as HCN; to roach 0.35 mg1‐1 as NH3‐N, 0‐11mg1‐1 as HCN, 10.1 mg1‐1 asNO2‐Nand 10mg‐1 as phenol. In order to define these LC50s, exposure periods within the range 0.3 days (phenol) to 14 days (nitrite) were required. Comparisons are made with other data and the tentative water quality ‘criteria’ proposed by the European Inland Fisheries Advisory Commission.
The possibilities of improving catchable fish stocks in lakes undergoing eutrophication
Authors: Bnińska M.
Published: January 2006

The area of Mazurian Lakeland is the biggest lake concentration in Middle Europe. Its lakes are subjected to various man‐made impacts and disturbances, resulting in many changes in the aquatic environment and the fish stocks. Most frequently these changes are typical of the process of accelerated eutrophication, and are connected with undesirable succession in the fish stocks. Generally, predatory species, which naturally regulate the stock and maintaiil its balance, disappear from the environment, as do other valuable fish species, e.g. coregonids. At the same time food resources (weed fishes, plankton) for those species develop abundantly.

Assessment of the management of lakes by one of the State Lake Fish Farms located in Mazurian Lakeland is presented against a background of various man‐made influences on the aquatic ecosystems in this region. The State Fish Farm under study manages 56 lakes of total area over 5800 ha. For each of these lakes detailed records were available of the commercial catches of particular species and their artificial stockings over a period of 31 years. These, their trends and inter‐relationships have been analyzed. Artificial stockings represented one of the best methods of counteracting adverse changes taking place in the fish stocks, with a simultaneous utilization of the productive potential of the lakes. Against this background, forecasts are made of the expected changes, and basic approaches to the proper management of the fish stocks are suggested.
Threadfin shad, Dorosoma petenense Günther, mortality: causes and ecological implications in a South‐eastern United States reservoir
Authors: McLean R. B. , Griffith J. S. , McGee M. V.
Published: January 2006

Cold stress was identified as an important factor influencing both reservoir‐wide mortality and impingement of threadfin shad, Dorosoma petenense, during the period October 1976 to April 1977 in Watts Bar Reservoir, Tennessee. Relative numbers and size frequency of impinged threadfin shad were similar to the relative numbers and size frequency of shad preyed upon by sauger, Stizostedion canadense, and skipjack herring, Alosa chrysochloris. This relationship implies that the factor mainly responsible for impingement, low temperature, also influences prey vulnerability. Threadfin shad made up 99% of the combined diet of sauger and skipjack herring from November until the threadfin shad disappeared in January. These predators did not readily switch to alternative prey in the short term, but by the next autumn 25–100% of the diet was alternative prey. Reappearance of threadfin shad the year following mass mortality and ability of the predators to vary their diet emphasize the resilient nature of some predator‐prey systems.
Growth, mortality, age composition and fisheries yields of fish from the Gulf of Aden
Authors: Edwards R. R. C. , Bakhader A. , Shaher S.
Published: January 2006

Tropical fish were collected by trawling in Yemeni waters. Age determinations were made on sections of vertebrae which were cross checked with scales. The values for the von Bertalanffy growth constants K were in the range 0.08–0.31. Total mortalities (Z) calculated from age compositions were in the range 0.31 to 0.67 for 11 species. The mean of 0.46 agreed closely with that derived from the formula of Pauly (1980a) of 0.45. Since the former included fishing mortality (F) in addition to natural mortality (M) it was suggested that a lower value be used in the Gulland (1968) yield formula: Y = 0.5 M Bo. Recruitment to the fishery for most species occurred by 3 years of age. The demersal fish stocks in Yemeni waters may not exceed 109×103 tonnes at the present time. Using a value for M of 0.3, the annual sustainable yield may be in the region of 16×103 tonnes.
Influence of some environmental variables on the ascorbic acid status of mullet, Mugil cephalus L., tissues
Authors: Thomas P. , Bally M. B. , Neff J. M.
Published: January 2006

The seasonal fluctuations in the ascorbic acid (AsA) and ascorbic acid 2‐sulphate (AsA 2‐sulphate) content of mullet, Mugil cephalus, tissues were examined. Ascorbic acid concentrations in brain, gill and hepatic tissues showed seasonal changes, but the pattern of AsA fluctuations in each tissue differed. The AsA content of mullet brains decreased during the summer, whereas hepatic AsA concentrations increased during this period and were maximal by the end of June. Hepatic AsA reserves declined after environmental water temperatures dropped below 18°C and reached a minimum (20 μg g−1) by the end of January. Greatest fluctuations in AsA content occurred in gill tissues, which had a four‐fold range of tissue concentrations. There were also seasonal changes in the AsA 2‐sulphate content of brain and hepatic tissues. These differences among mullet tissues in the seasonal patterns of AsA content may be due to diverse effects of environmental variables on tissue AsA reserves. The ability of hepatic and renal tissues of mullet and several other teleost species to synthesize AsA was also investigated. L‐gulonolactone oxidase activity was detected in all the species examined, but in all cases the biosynthetic capacity was less than a seventh that in goldfish, Carassius auratus, livers. Mullet appear to have only a limited capacity to synthesize AsA.
Digestive enzyme pattern of two stomachless filter feeders, silver carp, Hypophthalmichthys molitrix Val., and bighead carp, Aristichthys nobilis Rich.
Authors: Bitterlich G.
Published: January 2006

Activities of digestive enzymes (trypsin and amylase) of microplanktophagous silver carp, Hypophthalmichthys molitrix, and macroplanktophagous bighead carp, Aristichthys nobilis, were investigated in relation to pH in 10 different segments of the gut. In addition, the possible existence of ‘classical’ lysozyme in both species and cellulase in silver carp were scrutinized, but no activities were detected. Tryptic and amylolytic activities decreased sharply from fore‐gut to hind‐gut indicating an efficient reabsorption mechanism. Trypsin and amylase of both species had a pH optimum at 8.3 and 7.0 respectively. The relatively low pH of 6.4 in the fore‐gut of silver carp did not support an efficient operation of these enzymes, which was compensated by a higher enzyme concentration as compared to bighead carp. The latter, however, showed a higher pH of 7.3 in the fore‐gut and thereby maintained similar activities as silver carp. The distinction of herbivorous and omnivorous fish in terms of digestion mechanisms is discussed.
Ovarian cycling of tilefish, Lopholatilus chamaeleonticeps Goode and Bean, from the South Atlantic Bight, U.S.A.
Authors: Erickson D. L. , Harris M. J. , Grossman G. D.
Published: January 2006

Reproductive cycling and oocyte development were examined for female tilefish, Lopholatilus chamaeleonticeps Goode and Bean, captured in the South Atlantic Bight, U.S.A. A total of 752 female tilefish was collected during 15 sampling periods from May 1982 to December 1983. Reproductive cycling was quantified using four techniques: gross visual estimation of ovarian stages, histological examination of ovaries, follicle diameter measurements, and an ovarian index. The relative accuracies of these techniques also were evaluated. All four methods indicated that L. chamaeleonticeps was capable of spawning from March to June. Most spawning occurred between April and June. Ovarian development was positively correlated with the change in daylength. Follicular development was asynchronous, which is characteristic of multiple spawners. Folliculogenesis was similar to that in most oviparous teleosts.
Haematological characteristics of Clarias isheriensis Sydenham
Authors: Kori‐Slakpere O.
Published: January 2006

Haematological characteristics of Clarias isheriensis, a freshwater teleost, were established as a ‘working document’ upon which to base more extensive studies. Correlations were found with certain blood factors as functions of the physical parameters of length and weight. Other correlations which were not related to the physical size were also found. Factors which affect the haematological picture offish are discussed.
The effect of temperature on survival of carp fry, Cyprinus carpio L., in acidic water
Authors: Korwin‐Kossakowski M. , Jezierska B.
Published: January 2006

Studies of carp fry, Cyprinus carpio, showed that temperature elevation within the range of 18–26° C increases the mortality caused by lowering the pH of water. It was found that 26‐h acclimation in acidic water (mean pH 4.22) prolongs the survival of fish in water at pH 4.02–4.20. Carp fry obtained less oxygen in water at pH 4–0, as compared to pH 7–0. The differences–though insignificant–pointed to an adverse effect of acidification on the respiratory processes.
Avoidance response of two‐year‐old rainbow trout, Salmo gairdneri Richardson, to air‐supersaturated water: hydrostatic compensation
Authors: Lund M. , Heggberget T. G.
Published: January 2006

Vertical swimming responses of 2‐year‐old rainbow trout were tested with air saturated and air supersaturated water in tank experiments. The level of supersaturation varied between 115 and 125% total gas pressure. Control groups offish were kept in tanks with saturated water. No consistent vertical avoidance response was observed in the fish tested, but the mortality of fish restricted to the upper 30 cm of the tanks was significantly greater than fish free to sound to the whole depth of the tanks. It is concluded that the Norwegian stock of rainbow trout do not avoid air‐supersaturation at levels from 115 to 125% TGP by active hydrostatic pressure compensation. An incidental type of hydrostatic pressure compensation seemed to be taking place during these experiments, as indicated by different levels of mortality in tanks with different depths. This incidental type of hydrostatic compensation may explain the observed difference in tolerance to supersaturation between wild fish and fish kept in experimental tanks.
Diplostomiasis in sand smelt, Atherina presbyter Cuvier, from the Fleet, Dorset and its use as a population indicator
Authors: Bamber R. N. , Henderson P. A.
Published: January 2006

The population of sand smelt, Atherina presbyter, breeding in the Fleet, Dorset, shows a high infection of diplostomiasis. The population was studied in 1983 to clarify aspects for this parasitic condition previously analysed for the sand smelt population at Fawley, Southampton Water. All age classes showed a higher percentage infection and mean number of metacercaria per fish than at Fawley. Analysis of postlarvae and juveniles showed that infection can occur at 1 week old, and verified the hypothesis that the scales of older fish inhibit cercarial settlement. Circumstantial evidence suggests that Potamopyrgus jenkinsi may be the first vector host for this parasite, and the densities of this species and of nesting little tern colonies would account for the differential infection between these two sand smelt populations. The increase in infection of 2 fish at Fawley cannot be attributed to mixing with the Fleet population, and the different infection levels demonstrate population isolation. High levels of infection are limited to this part of the English Channel: sand smelt samples from around the coasts of the British Isles show minimal infection rates elsewhere and suggest a southerly distribution of the parasite, away from Atlantic oceanic waters.
Sex ratios and hermaphroditism in nemipterid fish from northern Australia
Authors: Young P. C. , Martin R. B.
Published: January 2006

Of 13 nemipterid species from coastal waters around northern Australia, nine show size‐related differences in sex ratio with males predominating at larger sizes. Histological examination of gonads shows that in Scolopsis monogramma S. taeniopterus and S. bilineatus this size‐related skew in sex ratio results from protogynous hermaphroditism and not from sexually differentiated growth rates as has been reported for other nemipterid species. There is also evidence that, in two other species, Nemipterus peronii and Pentapodus porosus, hermaphroditism may occur. Although the mechanism by which the gonads are transformed in S monogramma and S. taeniopterus differ markedly, there is evidence to suggest that in both species sex change is a post spawning event, successful initiation of which may require females to have achieved an advanced stage of vitellogenisis.
First record of the North Atlantic Morid fish, Laemonema latifrons Holt & Byrne, 1908, in the Mediterranean
Authors: Matallanas J.
Published: January 2006

The capture of a specimen of Laemonema latifrom Holt & Byrne, 1908, off Blanes (western Mediterranean) at a depth of 550m, in December 1983, is reported for the first time in this region.
The reproductive cycle of yellowfin bream, Acanthopagms australis (Günther), with particular reference to protandrous sex inversion
Authors: Pollock B. R.
Published: January 2006

Yellowfin bream, Acanthopagrus australis, of all age classes were collected from Moreton Bay, Australia. The species possessed typical sparid ovotestes in which the testis and ovary occur in separate zones. During the spawning period (June‐August) juveniles, functional males and functional females could be distinguished by the macroscopic appearance of the gonad. The sex ratio of males to females decreases with age, indicating protandrous sex inversion.

Histological and structural study of the ovotestis showed all fish have previtellogenic cells in the ovarian zone but only juvenile and male fish have developing spermatogenic cells in the testis. Most juveniles become functional males by the age of two years but a small proportion of juveniles develop directly into functional females (primary females). Protandrous sex inversion commences after the spawning period when male fish appear with spermatozoa and no other spermatogenic cells in the testis. During the period November‐January male fish with no spermatogenic cells are common and a reduction in size of the testis occurs so that by March‐April the ovotestis becomes structurally and histologically similar to the female ovotestis. Some fish remain functional males during their whole life‐history (primary males). In functional females vitellogenic cells are present in the ovary only during the spawning period and the testis remains very small in size.
Interaction of growth with social behaviour in Tilapia zilli raised in three different temperatures
Authors: Saclauso C. A.
Published: January 2006

Three thermal levels were tested on 10‐day old T. zilli fry obtained from one spawning to study the effects of temperature on the occurrence of growth depensation in the population reared under controlled environmental conditions. Results showed highest individual growth rate, mortality rates and growth depensation at 30 °C whilst the greatest biomass increase was obtained at an intermediate temperature (27 °C). The enhanced depensation and high mortality rates at the upper limit of the thermal gradient for growth of T. zilli were attributed to an alteration in the behaviour of fish which favoured a few, large, dominant and socially aggressive individuals.
Gastric emptying and the return of appetite in juvenile turbot, Scophthalmus maximus L., fed on artificial diets
Authors: Grove D. J. , Moctezuma M. A. , Flett H. R. J. , Foott J. S. , Watson T. , Flowerdew M. W.
Published: January 2006

Gastric emptying time in Scophthalmus maximus, when fed friable artificial pellets based on fishmeal, is composed of two phases:

(a) a delay time (td) during which the meal forms a bolus and which shortens with temperature, and

(b) an emptying phase (duration tend) which varies with meal size (S), body weight (W) and temperature (71 according to:

image

(where tend is in h, S is in g, W is in g and T is °C). During the emptying phase, stomach contents decrease curvilinearly according to:

image

(where St, & So is in g and t is in h) in which the instantaneous digestion rate, K, varies with fish weight and temperature as:

image

Food pellets were prepared which remained separate and did not form a bolus in the stomach; K increased if a given meal size was subdivided to increase surface area. If meal size was increased by ingestion of identical pellets, K decreased. After a satiation meal, appetite in young turbot returns in direct relation to the degree of stomach emptiness. When food is regularly available, young turbot feed steadily at a rate which maintains their stomachs at c. 85% maximum fullness. When trained to use demand feeders, the fish interact as a group to feed rhythmically, but feeding rate falls 33% to only two‐thirds of the previous rate since stomach fullness, and hence digestion rate (g h−1), is maintained at a lower level. Reduction in dietary energy density below 1 kCal g−1 increases gastric emptying rate and the turbot demonstrate partial compensation by increasing food intake. On energy‐rich diets, protein nitrogen and energy assimilation efficiencies remain high (97 5% and 91% respectively) irrespective of feeding rate and frequency.
Influence of temperature on number of circuli of first year scales of brown trout, Salmo trutta L.
Authors: Skurdal J. , Andersen R.
Published: January 2006

We studied the number of circuli of first year scales in brown trout fry originating from eggs and alevins incubated at 2 °C and 7 °C. During the first 31/2 months the 7 °C fry were reared at a lower temperature than the 2 °C fry whereas temperature was identical during subsequent months. The numbers of circuli increased with body length in both groups. However, both the number of circuli and the rate of circuli formation were higher in the group incubated at 7 °C and varied between 2 and 9 in the 2 °C–group and 5 to 14 in the 7 °C group. Differences among natural populations in the number of first year circuli may therefore be due to differences in incubation temperature. Experimental manipulation with incubation temperature can be used to mark large numbers offish permanently at low cost with a minimum of handling and hatchery stress.
Food of the roughhead grenadier, Macrourus berglax, Lacepede in North Norwegian waters
Authors: Eliassen J‐E. , Jobling M.
Published: January 2006

Over 30 different prey species were found in the stomachs of roughhead grenadiers, Macrourus berglax, caught at depths of approximately 700 m off the coast of northern Norway. Crustaceans and fish were the principal prey categories and large, mature grenadiers are classified as being generalist feeders taking predominantly benthopelagic organisms. There is evidence for an ontogenetic shift in dietary composition, with a change from benthic prey to an increased reliance on benthopelagic prey as the fish increase in size and this results in reduced intraspecific competition for food.
Exercise training and the stress response in rainbow trout, Salmo gairdneri Richardson
Authors: Woodward J. J. , Smith L. S.
Published: January 2006

Plasma levels of catecholamines, cortisol, and glucose were monitored in rainbow trout during a 6‐week forced swimming exercise programme. Compared to resting non‐exercised controls, resting trained fish had lower levels of epinephrine, norephinephrine, cortisol, and glucose during the last 3 weeks of training. Initially, trained fish that were swimming had higher levels of epinephrine than resting trained fish. After 2 weeks of exercise, swimming did not significantly elevate epinephrine levels in trained fish. Glucose levels were consistently greater in swimming fish than in resting fish. At the end of the training period, exercised trout had lower (15–20%) oxygen consumption rates while resting or swimming than unexercised fish.

After a 5‐month forced swimming exercise programme plasma levels of catecholamines and glucose were monitored in trained and untrained cannulated rainbow trout after 2 min of mild agitation. Trained fish showed an immediate (within 1 min) increase in the levels of epinephrine, but not norepinephrine and a delayed (within 15 min) increase in the levels of plasma glucose. Epinephrine levels returned to pre‐stress levels within 15 min. Untrained fish had no significant increase in the plasma levels of norepinephrine, epinephrine, or glucose.
The long‐term effects of auto‐immunologically induced granulomas on the testes of rainbowtrout, Salmo gairdneri Richardson
Authors: Secombes C. J. , Needham E. A. , Laird L. M. , Lewis A. E. , Priede I. G.
Published: January 2006

Complex giant cell granulomas were induced within the testis of mature rainbow trout following immunization with testis in Freund's complete adjuvant. Although such granulomas could completely fill the seminiferous tubules and sperm duct, they had no inhibitory effect on spermato‐genesis during a subsequent maturation. Germ cells developed normally around the periphery of the granulomas. The spermatozoa produced, however, were often prevented from being released by the presence of these long‐term granulomas within the sperm duct.
The induction of spawning behaviour in Puntius gonionotus (Bleeker) by treatment with prostaglandin PGF2α
Authors: Liley N. R. , Tan E. S. P.
Published: January 2006

Groups of Puntius gonionotus were brought into breeding condition by treatment with extracts of homoplastic pituitary material. Spawning in P. gonionotus includes a number of distinctive features which appear to be adaptations to reproduction in a riverine habitat. These features include the absence of a specific substrate requirement, the production of non‐adhesive, buoyant eggs, an elaborate circling display by the male, and a long spawning run during which gametes are dispersed across the current.

Spawning activity began 3–4 h after treatment with pituitary material. The relatively sudden increase in female responsiveness and attractiveness to males appears to coincide with the occurrence of ovulation. It is hypothesized that at this time the female releases a chemical signal which attracts and excites the male. Females participate in a number of spawning runs over a period of 30 min, thereafter female activity decreases rapidly.

Injections of a prostaglandin (PGF2a) were effective in inducing spawning activity in non‐gravid females. This finding provides support for the hypothesis, based on work with goldfish, Carassius auratus, that prostaglandin provides a link between periovulatory events in the ovary and the brain mechanism governing spawning activity.
Food composition and feeding habits of Astatotilapia flaviijosephi (Lortet) in Lake Kinneret (Israel)
Authors: Spataru P. , Gophen M.
Published: January 2006

Food composition and feeding habits of 102 specimens of Astatotilapia (Haplochromis) flaviijosephi (Lortet, 1883), collected in Lake Kinneret during 1973–1975 and 1981–1982, was studied. A. flaviijosephi is relatively abundant in the littoral zone of the lake. Females feed mostly on chironomid larvae, oligochaetes and amphipods whilst males consume mostly gastropods. Small fry are rarely preyed upon or collected by both sexes. The adaptive relation between the teeth and the type of food and the ecological status of A. flaviijosephi in the Kinneret ecosystem is discussed.
Genetics of susceptibility and resistance to disease in fishes
Authors: Price D. J.
Published: January 2006

The genetics of disease resistance in fish is examined. Major genes may cause skeletal or other phenotypic deformities and have also been implicated in the development of neoplasia. Others may affect viability through pleiotropic effects, or induce stress and therefore predispose to invasion by pathogens. Resistance usually appears, however, to be of a multifactorial nature. Variations in resistance between related species and between populations of the same species are described. In order to obtain an idea of the within‐population variation, heritability estimates have been obtained in some instances. Generally they are low, but may still indicate a sufficient level to be of use in a selection programme. The results of a limited number of selection programmes are described.
Age determination of eels, Anguilla anguilla (L): comparison of field data with otolith ring patterns
Authors: Berg R.
Published: January 2006

Otoliths of eels recaptured up to 5 years after tagging were used for comparative work on the determination of annual ring patterns. It was possible to locate false annuli caused by the tagging procedure and subsequently to define annual rings in otoliths within the known period between first tagging and final catch. This determination gave an estimate of the size of the annual zones. Growth depression caused by tagging could be shown in cross sections of otoliths. Well defined annulus patterns in micrographs of otoliths from tagged eels were compared with otoliths from untagged eels. This comparison allowed a dimensional calibration of the ageing method and the recognition of misleading additional rings. Mean annual length increments of 47.88 mm and Lx, of 123.3 mm were determined.
Histopathology of broken‐back syndrome in channel catfish
Authors: Miyazaki T. , Plumb J. A. , Li Y. P. , Lovell R. T.
Published: January 2006

Channel catfish, Ictdurus punctatus, were fed a vitamin C‐free diet under laboratory conditions. Specimens with ‘broken‐back’ syndrome had vertebral injury due to osteoporosis, abnormally increased ossification, and dysplasia. There was also impairment of systemic collagen fibres and atrophy of the pancreas and haemopoietic tissue.
The food of barramundi, Lates calcarifer (Bloch), in coastal and inland waters of Van Diemen Gulf and the Gulf of Carpentaria, Australia
Authors: Davis T. L. O.
Published: January 2006

Examination of the diet of Lates calcarifer, based on 3684 specimens of 4–1200 mm total length (T.L.), from two localities in north Australia showed it is an opportunistic predator with an ontogenetic progression in its diet from microcrustacea to macrocrustacea to fish. The increasing importance of fish in the diet of L. calcarifer in salt water (up to 87% of food consumed) involved a dietary shift from feeding on bottom‐dwelling forms to pelagic forms. There were few differences in the diet of L. calcarifer between the two localities. Cannibalism was rarely encountered in the Gulf of Carpentaria although it was significant (11–4% of the diet of L. calcarifer of 1001–1200 mm T.L.) in Van Diemen Gulf. A significant correlation between predator and prey length was found for Ariidae, Dorosomidae, Engraulidae, L. calcarifer, Mugilidae and Polynemidae. The maximum prey/predator length ratio observed was 0–61 for the dorosomid, Nematolosa erebi.
Digestive secretions of lake sturgeon, Acipenser fulvescens, during early development
Authors: Buddington R. K.
Published: January 2006

Digestive secretions of lake sturgeon were analysed for 60 days post‐hatch. Three developmental phases were observed. During the yolk‐sac stage (days 1–16) the digestive system differentiated and digestive enzyme concentrations were low. Initiation of gastric secretion was concurrent with establishment of active feeding (days 14–18). Peptic and tryptic activities continued to increase thereafter. Amylolytic and lipolytic activities were highest during the larval feeding phase and then declined following metamorphosis of the larvae to juveniles (days 24–30). Changes in the digestive enzyme complement were age related, not dietarily induced, and appeared to correspond with the different feeding habits and, possibly, nutritional requirements of the distinct life history stages.
Consequences of thermal change on the myofibrillar ATPase of five freshwater teleosts
Authors: Heap S. P. , Watt P. W. , Goldspink G.
Published: January 2006

Myofibrillar ATPase activity was measured in the epaxial musculature of five freshwater species of fish acclimated to extremes of temperature within their tolerance ranges. Changes in the enzyme activity were apparent in carp, tench and roach, cold acclimated fish (10°C) having higher enzyme activity levels than hot acclimated fish (28°C). Such changes were not apparent in eels or brook trout. Alteration of the enzyme activity took less than 4 weeks, and was totally reversible. This suggests that seasonal adaptation to environmental temperatures is possible, thus maintaining locomotory efficiency.
Purification of carp putative eosinophils on metrizamide gradients
Authors: Hendrick M. , DiNapoli A. , Cammarata P. , Pincus S.
Published: January 2006

A protocol for the purification of carp eosinophils on metrizamide gradients is presented. Density gradient centrifugation is a new approach to the study of eosinophils in fish. It provides enriched populations of viable eosinophils necessary for in vitro functional assays. Eosinophils purified from the peripheral blood of carp resemble mammalian eosinophils by light and electron microscopy. They are indistinguishable from carp neutrophils which have a different density and morphology.
Putative immune response of rainbow trout, Salmo gairdneri, to Diplostomum spathaceum infections
Authors: Stables J. N. , Chappell L. H.
Published: January 2006

The immune response of rainbow trout to infection with the cercariae of the digenean parasite Diplostomum spathaceum was investigated. Rainbow trout infected with cercariae at weekly intervals, or injected with a suspension of dead cercariae, did not produce a specific humoral response against D. spathaceum cercariae, as tested using immunoperoxidase, agglutination and cytotoxicity assays. However, a significant difference occurred in the rate of infection of rainbow trout given weekly exposure to cercariae of D. spathaceum in winter and summer. Rainbow trout injected with a suspension of dead cercariae acquired significantly fewer metacercariae than controls when exposed to a challenge infection. This suggested a specific immune response by the host and is the first example of a reduction in the infection rate of rainbow trout immunized against a digenean parasite, when exposed to a challenge infection.
Fish skin surface lipids: phospholipids
Authors: Mittal A. K. , Nigam G. D.
Published: January 2006

Phospholipid components of skin surface secretions of four Indian freshwater fishes were analysed using different solvent systems in one‐dimensional and two‐dimensional thin‐layer chromatography, and quantified using a spectrophotometer. The phospholipid pattern of the skin secretions is similar to that of membrane lipids. Phosphatidyl choline and phosphatidyl ethanolamine are the major components constituting approximately two‐thirds of the total phospholipids. Sphingomyelin and phosphatidyl serine are present in relatively low quantities. Phosphatidic acid, phosphatidyl glycerol, lysophosphatidyl choline and lysophosphatidyl ethanolamine, which may be important metabolic intermediates, are present in very low quantities in the skin surface secretions of all four species. It is suggested that the lipids are derived from membranous profiles in the secretions of skin glands, extrusion of membrane‐bound vesicles from surface epithelial cells, and exfoliated cells. The results are discussed in relation to the biochemical and biological significance of these lipids in the skin secretions.
Influence of dietary protein and lipid levels on growth, body composition and utilization efficiencies of Arctic charr, Salvelinus alpinus L.
Authors: Tabachek J. L.
Published: January 2006

Growth, body composition and feed utilization were evaluated for Arctic charr fed a control diet and nine practical diets formulated to contain three protein levels (34, 44 or 54%) at each of three lipid levels (10, 15 or 20%). Fish were raised for 24 weeks at 12° C. Increasing either dietary protein and/or lipid resulted in improved weight gain, feed efficiency and energy retained. Protein efficiency ratio and protein retained were directly related to dietary lipid and inversely related to dietary protein. A sparing effect of lipid on protein was evident where, at each protein level, Arctic charr utilized protein more efficiently with each increase in dietary lipid. Levels of 34% protein and/or 10% lipid were well below the requirements for Arctic charr (initial weight, 4.6 g). Within the range tested, the dietary combination of 54% protein with 20% lipid maximized weight gain and feed efficiency and resulted in fish with low liver and body lipid contents. However, if lowest feed cost per kg gain is an important factor, the 44% protein—20% lipid diet would be less expensive to use, although it results in a minor reduction in growth potential.