bluuebunny/crossref_metadata_2025 huggingface dataset:
The ecological interaction between arctic charr, Salvelinus alpinus (L.), and the plerocercoid stage of Diphyllobothrium ditremum
Authors: Halvorsen O. , Andersen K.
Published: January 2006

Six hundred and two arctic charr, Salvelinus alpinus, from a small lake (30 ha) were examined for infection with plerocercoids of Diphyllobothrium ditremum the only species of this genus present; 466 (77.4%) harboured the parasite in an overdispersed infection. The prevalence of infection increased with age and reached 100% at 7+ years for males and 8+ years for females. The rate of infection appeared to be related to the feeding biology of the charr which did not change within the age span studied. The rate of increase in density of infection (plerocercoids per fish) decreased with age as did the degree of overdispersion. It is concluded that the infection probably induces mortality in the fish population, and that such mortality is dependent on parasite density.
Structural studies on the thymus of the dogfish, Scyliorhinus canicula L.
Authors: Pulsford A. , Morrow W. J. W. , Fänge R.
Published: January 2006

Histological and ultrastructural studies of the thymus of the dogfish, Scyliorhinus canicula L., revealed paired lobular masses above the first two gill arches of embryonic and newly hatched dogfish, involuting at approximately 3 weeks. It did not have defined cortex and medullary regions and ultrastructural investigations showed the tissue to be composed mainly of a range of different sized lymphocytes within a connective tissue capsule and reticular epithelial cell framework. Lymphoblasts often in mitosis were also present being more electron lucent and larger than lymphocytes. Macrophages contained cellular debris and frequently whole small lymphocytes. A cell with cytoplasmic granules was occasionally observed.
Resource utilization and coexistence of three species of sticklebacks (Gasterosteidae) in tidal salt‐marsh pools
Authors: Walsh G. , FitzGerald G. J.
Published: January 2006

Food resource partitioning in a community consisting of three sticklebacks (Gasterosteidae) was studied in a tidal salt‐marsh near Isle Verte, Québec in the St Lawrence Estuary. From May to July 1981 stomachs of all species were analysed. In general four prey items composed greater than 70% of the diet. There were differences in the relative proportions of prey items eaten between the sexes and species and on the different sampling dates, indicating resource partitioning. However, experiments, where allopatric and sympatric populations were established in tidal pools, did not reveal and significant shift in either type of prey or size of prey consumed, suggesting that food competition was unimportant. Microhabitat partitioning was also observed between the three species which may have served to reduce interspecific competition for food.
Stress‐induced water permeability changes in the tropical cichlid, Oreochromis niloticus (Trewavas)
Authors: Adedire C. O. , Oduleye S. O.
Published: January 2006

The effect of short‐term, experimentally‐induced stress on the branchial water permeability of Oreochromis niloticus was studied. Both handling and thermal stress increased water permeability but apparently by different mechanisms. The enhancement of water permeability by acclimation temperatures and acute temperature changes had Q10 of 3.52 and 2.24 respectively. Environmental sodium concentration and acute hypoxia had no effect while hypercapnia and mild anaesthesia decreased water permeability. Both hypercapnia and mild anaesthesia probably elevated arterial pCO2 with a concomitant reduction of metabolism.
Epidermal condition in post‐spawned winter flounder, Pseudopleuronectes americanus (Walbaum), maintained in the laboratory and after exposure to crude petroleum
Authors: Burton D. , Burton M. P. , Idler D. R.
Published: January 2006

Skin samples were taken, during the post‐spawning period, from Pseudopleuronectes americanus maintained in both stationary and in running‐water systems, and after exposure to Venezuelan crude oil in each system. Comparisons with skin taken freshly from an inshore population revealed that dissociation of epidermal tissue, epidermal thinning and reduced epidermal melanophore frequency normally associated with the postspawning period were not so apparent after laboratory confinement and were even less pronounced after exposure to crude oil. In post‐spawned, laboratory maintained flounders, there was also correlation between epidermal thickness and the weight of the fish. Indications from the stationary system suggest that stress associated with environmental conditions may evoke mucigenesis in the superficial epidermal cells as distinct from the goblet cells.
Compensatory growth in the rainbow trout, Salmo gairdneri Richardson
Authors: Dobson S. H. , Holmes R. M.
Published: January 2006

The effect of a period of starvation and subsequent refeeding on the weight and length of rainbow trout at different times of the year has been investigated. Fish that have been starved for 3 weeks and then fed for 3 weeks show a weight gain equivalent to or greater than that of fish fed normally for the 6 week period, in four out of the five periods studied. The study provided evidence of the adaptation of the fish to starvation followed by what may be termed compensatory growth once feeding was resumed. The length changes of the fish indicate that the weight gains were due to growth rather than increases in gut fat deposits or increased water uptake.
Production of metabolic and waste products by intensively farmed rainbow trout, Salmo gaivdnevi Richardson
Authors: Clark E. R. , Harman J. P. , Forster J. R. M.
Published: January 2006

The pollution production rate as measured by the increase in the amounts of ammonia, phosphate, nitrate, urea, and faeces in an intensive fish farm is described and is related to the amount of food fed per day or the biomass weight. Pollution production varied with fish size. Main pollutants produced per kg food fed per day were ammonia 31–37 g; phosphate 5.2–5.9 g; nitrate 9–15 g and suspended solids 40–9O g. Expressed as g kg−1 fish produced per day ammonia ranged from 0.3–0.8 g; phosphate 0.067–0.17 g; nitrate 0.13–0.21 g and suspended solids 0.80–0.94 g. These rates differ from those reported in previous studies and these differences may be attributed to the design of the Shearwater farming system which involves self cleaning, intensively stocked tanks, a system which ultimately gives a more accurate assessment of pollution rates.
Body condition and nutritional ecology of Oreochromis mossambicus (Pisces, Cichlidae) populations of man‐made lakes in Sri Lanka
Authors: De Silva S. S.
Published: January 2006

The nutritive quality of ingested material of adult Oreochromis mossambicus wild populations from 12 perennial, man‐made lakes were evaluated for four climatic seasons. The seasonal variation in condition of each population, and the overall condition of each population, considered as the theoretical weight of a 20cm individual, was computed from the length‐weight regressions, which were curvilinear. The mean overall condition of the O. mossambicus reservoir population was 152.6 g (s.d.± 9.5) and ranged between 139.8 and 167.8 g. Distinct patterns in the seasonal changes in condition of an individual population were not apparent. The mean percentage of protein and total organic matter (TOM) and calorific content (kJg−1) of the ingested material were 20.7% (s.d.± 3.7; range 9.6–35.2%), 46.0% (s.d.± 9.8; range 20.9–73.7%) and 11.6 (s.d.± 3.4; range 4.6–20.9) respectively. The amount of each of the above components for any one population varied seasonally in relation to the changes in feeding habit. The protein content of the ingested material of those populations devouring predominantly detritus also showed seasonal variability. The amount of protein (mg) in the digestible total organic matter (DTOM) and the calorific content (Cal) in the ingested material were related to the TOM content as follows:

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The overall body condition (BC) of O. mossambicus populations was linearly rebated to the digestible protein: energy ratio (PER) thus:

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The study indicates that a mixed diet was superior in nutritional quality to a single‐component diet. especially with respect to detrital material.
Population biology of the myctophid fish Gymnoscopelus nicholsi (Gillbert, 1911) from the western South Atlantic
Authors: Linkowski T. B.
Published: January 2006

Thirty‐three collections of Gymnoscopelus nicholsi were made between 1976 and 1981 in the South Atlantic using both krill and bottom trawls. In the Antarctic waters the main part of the stock consisted of adult fish 3–7 years old, characterized by a benthopelagic mode of life. Fish of year‐class I were observed only in the vicinity of South Georgia, South Sandwich Islands and the Scotia Sea; year‐class II individuals were absent from Antarctic samples. In the notal zone of the western South Atlantic, fish aged 1–5 years were found. The existence of only one population in the region is a possible explanation of these findings: this population is divided into a pelagic stock of juveniles and sub‐adults which occur in the offshore waters of the western South Atlantic and benthopelagic stocks of adults distributed over the slope regions off Argentina, South Georgia and Antarctic archipelagos.

The computed values of K (von Bertalanffy growth) were 0.48, 0.41 and estimated total annual instantaneous mortality rates (Z) were 0.45, 0.67, and 0.70 for South Georgia, South Shetlands and notal zone of western South Atlantic stocks, respectively.
Serum calcium concentrations in white sucker, Catostomus commersoni Lacepède, and bluegill, Lepomis macrochirus Rafinesque, in northern Wisconsin lakes: relation to pH and waterborne calcium
Authors: Wiener J. G. , Jacobson R. A. , Schmidt P. S. , Heine P. R.
Published: January 2006

We measured serum calcium concentrations in mature white suckers and bluegills collected from clear‐water Wisconsin lakes before spawning. The mean serum calcium concentration in female white suckers was greater in a circumneutral lake than in two naturally acidic lakes, whereas mean concentrations in fish from the two acidic lakes did not differ. Serum calcium concentrations in female bluegills from four acidic and four circumneutral lakes varied among lakes, but no relation was apparent between serum calcium level and either lake pH or waterborne calcium. In contrast, a strong negative correlation between mean serum calcium concentration and relative density of bluegill populations in the eight lakes was observed, suggesting that serum calcium levels in this species are affected by density‐dependent factors. Mean serum calcium concentrations were substantially lower in mature male bluegills than in females, which is the norm prior to spawning. We hypothesized that serum calcium levels in female white suckers are depressed by exposure to pH 6.0 or less in calcium‐poor waters. The utility of serum calcium concentrations, measured before spawning, as a measure of pH‐related stress on populations of white suckers and other synchronous spawners merits further study. However, this measure is probably not useful for evaluating acid stress on fish species such as the bluegill, which have asynchronous reproductive cycles.
Cytochemical enzyme staining of fish lymphocytes separated on a Percoll gradient
Authors: Blaxhall P. C. , Hood K.
Published: January 2006

Brown trout (Satmo trutta L) lymphocytes were shown to separate into two fractions on a Percoll discontinuous gradient, with 53% of the cells in the 1.07gl‐1 fraction. The cells from the two fractions showed equal enzyme activity when stained for acid esterase and acid phosphatase. About 70% of the lymphocytes gave a positive enzyme reaction, which if the reaction is comparable with mammalian lymphocyte cytochemistry would indicate they were T‐lymphocytes. There appears to be increasing evidence among fish for the existence of T‐ and B‐lymphocytes, and cytochemical staining could prove a comparatively convenient method for their demonstration.
Population dynamics of migratory trout, Salmo trutta, in a Lake District stream, 1966–83, and their implications for fisheries management
Authors: Elliott J. M.
Published: January 2006

A short review summarises the chief conclusions of an 18‐year investigation of the population dynamics of migratory trout, Salmo trutta L., in a Lake District stream. The chief factors affecting growth, survival and production have been identified and their effects summarized in a series of mathematical models. The implications of this work are discussed in relation to long‐term investigations, data analysis and modelling, and the scientific management of trout populations. It is shown that mathematical models, based on long‐term investigations, can be used to assess the effects on a fish population of changes due to natural causes (e.g., droughts and spates) or human activities. One of the main objectives of future work should be the development and improvement of models that can be used as tools for the conservation and management of fish stocks.
Salmon stock and recruitment, and stock enhancement
Authors: Solomon D. J.
Published: January 2006

The precise nature of the stock and recruitment relationship in natural populations is of vital importance to any attempt at stock enhancement by removing or by‐passing a limiting factor, or at management by manipulation of spawning stock. In this paper the evidence for and against a dome‐shaped stock and recruitment curve is reviewed, and consideration given to several factors which complicate the conventional, simplistic interpretation of density‐dependent mortality. These include environmentally mediated changes in ‘carrying capacity’, distribution of spawning, and the need to consider whole river systems. The implications of these factors for fisheries management and stock enhancement are discussed.
Discharges of pesticides to the Rivers Mole and Taw, their accumulation in fish flesh and possible effects on fish stocks
Authors: Hamilton R. M.
Published: January 2006

A discharge of aldrin and dieldrin caused mortality of salmonid fry in a hatchery. Pesticide residues in fish flesh and resulting management action are described. Differences in wild fish stock densities could be due to pesticides but other possibilities are explored. Dieldrin was widely distributed, even at control sites, at levels considered potentially dangerous to piscivores. A further point source was traced and widespread environmental contamination was observed.
Cost effective sampling of fish populations in large water bodies
Authors: Hickley P. , Starkie A.
Published: January 2006

Estimation of fish population size in large water bodies is a long‐standing problem. In addition to sampling difficulties there are economic constraints. Case histories are presented showing how a range of large habitat types have been surveyed and the methods are discussed in terms of success and cost: (a) the status of the River Severn fish population was monitored by postal questionnaires addressed to contest fishermen and proved extremely cost effective; (b) a predator cull and population estimate for a 35 ha lake was made by sequential netting of sections and the nature of the result questioned the validity of a less labour intensive qualitative approach to lake surveys; (c) an electric fishing technique has been developed for surveying canals and comprises a boom‐mounted array of ten anodes which gives worthwhile improvement in performance when compared to a few hand‐held electrodes; (d) attempts have been made to remove roach from a 240‐ha water supply reservoir, using echo‐sounding to locate shoals prior to capture with a purse seine.
Survey methodology for fish population assessment within Anglian water
Authors: Coles T. F. , Wortley J. S. , Noble P.
Published: January 2006

Basic data required for the maintenance, improvement and development of inland fisheries within the Anglian Water Authority area are derived from surveys carried out since 1977. All open river systems are sampled on a 3‐year cycle and basic data are obtained on species composition, density and biomass as well as year‐class structure and growth rates of dominant species.

The netting and electrofishing gear and techniques used to obtain quantitative and semi‐quantitative samples from rivers, drainage channels and the Norfolk Broads are described and their advantages and disadvantages discussed. The mark and recapture and multiple removal techniques employed with these methods are described and an assessment given of sampling efficiency in different situations.
Biochemical genetic stock structure of the southern African anchovy, Engraulis capensis Gilchrist
Authors: Grant W. S.
Published: January 2006

The geographical distributions of inherited biochemical markers were used to measure the amount of genetic isolation between stocks of Namibian and South African anchovy, Engraulis capensis. A contingency‐table analysis of allele frequencies for 10 polymorphic protein‐coding loci revealed no significant frequency differences between spawning areas. The average Nei genetic distance between samples was 0.0003 and there were no geographic trends in the amount of genetic distance between populations. Average population heterozygosity for 31 loci was 0.115 and this accounted for 99.26% of the total genetic variation. The remaining 0.24% was due to all temporal and spatial differences combined. The observed amount of genetic divergence between populations was used to estimate the amount of migration between spawning areas, using the stepping‐stone model of migration. As few as 13 migrants may account for the observed genetic divergence between spawning areas. The validity of using the genetic stock concept in the management of marine fishes is discussed.
Cadmium‐induced changes in gill morphology of zebrafish, Brachydanio rerio (Hamilton–Buchanan), and rainbow trout, Salmo gairdneri Richardson
Authors: Karlsson‐Norrgren L. , Runn P. , Haux C. , Förlin L.
Published: January 2006

Freshwater zebrafish and brackish water rainbow trout were exposed to different concentrations of cadmium for up to 6 weeks. The gill morphology was examined by light and electron microscopy, and a morphometric analysis was performed. The morphometric study of the secondary lamellae revealed an increase in the portion exterior to the basal lamina, resulting in an increased diffusion distance, after exposure to cadmium concentrations of 10μg l−1 and above. In both species this was due to an increase in volume of the non‐tissue spaces of the secondary lamellar epithelium. Furthermore, the water space between neighbouring secondary lamellae was clearly reduced. Morphological examination revealed some gross alterations compared with control fish. These initially consisted in curling of the secondary lamellae and finally resulted in local teleangiectasia. Partial lifting of the secondary lamellar epithelium from the pillar cells resulted in large non‐tissue spaces which were invaded by leucocytes. The first sign of degeneration was observed in the chloride cells, which were characterized by a dispersed cytoplasm and a smooth apical plasma membrane.
Temperature preference and heat resistance of grass carp, Ctenopharyngodon idella (Valenciennes), bighead carp, Hypophthalmichthys nobilis (Gray), and their F1 hybrid
Authors: Bettoli P. W. , Neill W. H. , Kelsch S. W.
Published: January 2006

Acute temperature preferenda and critical thermal maxima were determined for 23°C‐acclimated stocks of grass carp, bighead carp and their F, triploid hybrid. Preferred temperature and critical thermal maximum of the hybrid were significantly higher than those of the grass carp (female parent), which is consistent with prior field observations. The hybrid's values for both parameters also were significantly higher than those of the bighead carp. These results comprise experimental evidence for substantial heterosis in the thermal physiology of fishes.
Frequency of chromosomal aberrations in the rainbow trout, Salmo gairdneri Rich., exposed to five pollutants
Authors: Al‐Sabti Kabil
Published: January 2006

This work presents the results of investigations of cytogenetic changes produced by pollutants of a water ecosystem (phenol, decamethrine, Malathion, Neguvon and crude oil). The changes have been measured by observing frequency of chromosomal aberrations in the tissues of gills and kidney of rainbow trout exposed to pollutants. The fish were exposed to two dose levels of the pollutants, the lowest being the legislative maximum permissible concentration in the waters of Yugoslavia, which were used as a dose‐response for the highest investigated concentrations. Exposure to the water polluted by chemical pollutants under investigation, raised the frequency of aberrations compared to the controls.
Occurrence and distribution of Clinostomum tilapiae Ukoli, 1966 and Euclinostomum heterostomum (Rudolphi, 1809) metacercarial infections of freshwater fish in Venda and Lebowa, southern Africa
Authors: Britz J. , Van As J. G. , Saayman J. E.
Published: January 2006

During 1980 to 1982, parasitological surveys were carried out at large impoundments in Venda and Lebowa, southern Africa, coinciding with fish harvesting programmes. Of the various fish species examined, only Oreochromis mossambicus was found to be infected by Clinostomum tilapiae prevalent in the gills, and Euclinostomum heterostomum prevalent in the muscles. Distribution records and infection statistics are presented for these two parasite species.
Accelerated photoperiod advances seasonal cycle of sea water adaptation in juvenile Baltic salmon, Salmo salar L.
Authors: Clarke W. C. , Lundqvist H. , Eriksson L.‐O.
Published: January 2006

Two‐summer‐old Baltic salmon parr were brought to the laboratory and reared at 11 °C from February until early June under a simulated natural photoperiod and an accelerated photoperiod cycle in which the summer solstice was advanced by 2 months. The pattern of development of the ability to adapt to sea water was assessed by means of a periodic 24‐h challenge test with 25%o seawater. Both the increase in seawater adaptability and its decline occurred earlier under accelerated photoperiod. The synchronisation of the smolting cycle is discussed in relation to the environmental cues provided by photoperiod.
Descent of European silver eels, Anguilla anguilla L., in a Norwegian watercourse
Authors: Haraldstad Ø. , Vøllestad L. A. , Jonsson B.
Published: January 2006

Seaward migration of silver eels occurred at nights during autumn at decreasing water temperature. Maximum migration‐rate occurred mid‐October at medium and decreasing water discharge. Most eels descended in the first quarter of the lunar cycle, few eels descended at full moon. Most males and small females migrated earlier in the season than the larger females. The migration speed of silver eels in fresh water was independent of body length.
Effects of 17α‐methyl‐testosterone on spermatogenesis and spermiation in the grey mullet, Mugil cephalus L.
Authors: Weber G. M. , Lee Cheng‐Sheng
Published: January 2006

Diets containing 17α‐Methyl‐testosterone were given to grey mullet, Mugil cephalus, during the refractory period in its reproductive cycle at the dosage of 25 mg or 12.5mgkg−1 fish. Fish in experiment I were fed the diet containing methyl‐testosterone every day for 55 weeks, and fish in Experiment II were fed the same diet daily for the first 10 weeks, and three times per week for the next 42 weeks. Fish were checked for the presence of sperm weekly or bi‐weekly and tested for fertility during the spawning season. Terminal gonad weights and histology were compared with control groups. This study demonstrated that male mullet will mature 3 weeks or less by oral administration of 12.5 mg methyl‐testosterone kg−1 fish daily. Fish can then be maintained in mature condition by feeding them methyl‐testosterone at 12.5 mg kg−1 three times per week.
Osmotic regulation in the Sheepshead Minnow Cyprinodon variegatus Lacépède
Authors: Nordlie Frank G.
Published: January 2006

Plasma osmotic regulation was evaluated in Cyprinodon variegatus acclimated to salinities from fresh water to 120%. These fish showed roughly stable regulation in the range from 0.3% to 70%. Fish acclimated to fresh water showed an increased plasma concentration over those in 0.3%, thought to result from a higher Ca++ level in fresh water. Plasma concentrations rose abruptly at salinities above 70%. Osmotic regulatory characteristics of C. variegatus were compared with data for other extremely euryhaline species with expectation of a graded series of responses, species showing greatest fresh water tolerance demonstrating widest ranges of regulation and with lowest plasma concentrations. Results were not consistent with expectations. The range of ambient salinities over which good regulation of plasma concentration was shown was found to be directly correlated with the magnitude of the salinity tolerance range of all of the species compared. Forms with greater fresh water affinity generally, but not uniformly, showed the lowest plasma concentrations in the region of hyperosmotic regulation.
Experimental studies on some trophic relationships in juvenile pike, Esox lucius L.
Authors: Kaushik S. J. , Dabrowski K. , Luquet P.
Published: January 2006

A postprandial increase in ammonia nitrogen excretion and oxygen consumption rates was observed in juvenile pike fed a natural diet or an artificial dry diet. Specific growth rate of natural diet fed pike (2.4%) was lower than that of pike fed the artificial diet (3.1%). Fifty per cent of ingesta was evacuated within 5–6 h in pike of 25 mg body weight and 9–10 h in those weighing 150mg. Daily nitrogen excretion rates were related to body weight. Respiratory quotient and energy retention efficiency were affected by the nature of the diet ingested by pike. Parameters of the energy balance (losses, retention, increment due to feeding) were related to energy intake.
Drug induced structural changes in olfactory organ of channel catfish Ictalurus punctatus, Rafinesque
Authors: Lewis D. H. , Tarpley R. J. , Marks J. E. , Sis R. F.
Published: January 2006

The fish anaesthetic tricaine methanosulfate destroyed the cilia on olfactory sensory epithelia of channel catfish, when fish were exposed to tranquilizing doses of the drug. Cilia on the non sensory epithelium appeared to be unaffected by multiple exposures of the drug. Sensory cilia regenerated within 28 days after exposure.
Recruitment control and production of market‐size Oreochromis niloticus with the predator Lates niloticus L. in the Sudan
Authors: Bedawi R. M.
Published: January 2006

Experiments were conducted in earth ponds (242–1260m2) to evaluate the Nile perch (Lates niloticus L.) as a predator for recruitment control and the production of marketable Oreochromis niloticus L. in the Sudan. Supply of the predatory fish was maintained by induced spawning of L. niloticus brooders by raising the water level in a 1–0 ha earth pond. Lates niloticus fingerlings (7–5 cm total length) were then stocked with same size O. niloticus at the ratios 1:5, 1:10 and 1:15, Lates:Oreochromis, respectively. Over a period of 7 months Lates niloticus reduced young 50g) Oreochromis population and enhanced the production of preferred‐size ( 200 g) Oreochromis. The ratio 1:5 Lates:Oreochromis was established to be the most desirable for Lates‐with a total production of 0.2428 kg/m2 of O. niloticus with 55.7% (by weight) at the target size averaging 287.5g. The ratios 1:10 and 1:15 produced 0.2106 and 0.2153 kg m2 of O. niloticus, with 49.4% and 16.9% averaging 235.0 and 210.0 g, respectively.
Changes in circulating blood cell levels of rainbow trout, Salmo gairdneri Richardson, following acute and chronic exposure to copper
Authors: Dick P. T. , Dixon D. G.
Published: January 2006

Significant leucopenia, predominantly the result of a large reduction in lymphocyte concentration, was observed in rainbow trout exposed to 301 μg1−1 copper for 24h. A strong trend (P = 0–085) toward reduced erythrocyte concentration was also apparent. The pattern of haematological change after chronic exposure (118 μg 1−1 copper for 16 weeks) was substantially different. With the exception of a significant increase in neutrophil concentration (neutrophilia), all blood cell concentrations had returned to control levels.
Reproductive biology and growth of the goatfish, Parupeneus barberinus (Lacepede), in Aqaba, Jordan
Authors: Wahbeh M. I. , Ajiad A.
Published: January 2006

Monthly changes in the gonadosomatic index indicate that the main spawning season of Parupeneus barberinus in Aqaba extends from May to August for females and from May to June for males. Males in the 4 years age‐group (63–4%) and the 5 years age‐group (65–1%) are predominant. The von Bertalanffy growth equation parameters calculated from mean total length data are: Lα= 32–8cm; K=0–225; (to=−0–73 for males and Lα= 32–7cm; K=0–206; to=−0.82 for females. The length‐weight regression coefficients for males (2.85) and females (2.8) are not significantly different and they indicate a negative allometric growth. There is no significant change in condition factor with age.
The dorsal light reactions of larval and metamorphosing flatfish
Authors: Neave D. A.
Published: January 2006

Before metamorphosis, plaice and turbot show dorsal light reactions generally similar to those of other species, suggesting that their balance mechanisms are also similar, and that their utriculi are functional. The reactions are unusual in one respect in that larvae of both species tilt away from light incident from below the horizontal. In turbot, during metamorphosis, the null position (that taken up when illumination is from directly above) becomes gradually inclined to the right until the larva is horizontal at the end of metamorphosis. There is evidence that the null position of the static system is reset to an inclined position during this change. In plaice, during metamorphosis, the shift in null position is smaller, in the opposite direction, and at the end of metamorphosis there is a rapid change to a horizontal position. The null position of the static system does not appear to be reset. In plaice the influence of light on balance increases during metamorphosis, possibly due to it affecting the brain or the otolith organs. This is not seen in turbot, but light has a strong influence on the balance of this species both before and during metamorphosis. At the end of metamorphosis both plaice and turbot appear to utilize only static information from the sacculi and lagenae. Light could be seen to influence balance in swimming turbot, but not in plaice.
A comparison of the pond culture of carp, Cyprinus carpio L., in Britain and mainland Europe
Authors: O'Grady K. T. , Spillett P. B.
Published: January 2006

In recent years the requirement for carp in the U.K. has escalated, mainly due to the restocking market. This demand cannot be met from mainland Europe because of import restrictions and home production has increased. Freshwater coarse fish farming has been historically unimportant in Britain and few scientific data exist for pond culture under British conditions. In general, continental guidelines are followed but the growing‐on ponds are smaller. The climate and the nature of the sites have often resulted in unreliable spawning. First year survival and growth tends to be poorer but growth rates in the second year are comparable. Carp for restocking (c. 300 g) can be reared in 2 years and carp for the table (c. 1000 g) can sometimes be produced in 3 years. Levels of production, however, compare favourably with more traditional carp culture, up to 480 kg ha−1 per year using extensive cultivation and up to 2200 kg ha−1 per year with intensive rearing and pelleted foods. The sites in Britain for which data exist have, however, been eutrophic in contrast to the more mesotrophic sites on the mainland. This apparent difference in base, line productivity may explain the relatively good production performance so far in Britain.
Effects of sampling on blood parameters in the rainbow trout, Salmo gairdneri Richardson
Authors: Railo E. , Nikinmaa M. , Soivio A.
Published: January 2006

The effects of sampling and short‐term storage of blood samples on the blood parameters of rainbow trout were evaluated by comparing values obtained from resting fish sampled via cannulae and from fish sampled by cardiac puncture. Sampling stress causes an increase in haematocrit value and a decrease in mean cellular haemoglobin concentration, indicating red cell swelling. These changes are aggravated by consecutive storage of samples. Also, blood ionic balance is affected. The K+ concentration of plasma increases and plasma Cl− concentration decreases owing to sampling. During storage the plasma K+ concentration decreases far below resting levels in samples taken by cardiac puncture, whereas plasma Cl− level returns to pre‐stress levels. Owing to the sampling‐ and storage‐induced changes in blood parameters, care must be taken to ensure that similar sampling procedure is employed throughout to allow reliable comparisons between groups to be made.
Feasibility of protecting rainbow trout, Salmo gairdneri Richardson, by immunizing against the eye fluke, Diplostomum spathaceum
Authors: Speed P. , Pauley G. B.
Published: January 2006

Rainbow trout, Salmo gairdneri, were immunized with sonicated metacercarial antigens from the eye fluke, Diplostomum spathaceum. Immunization increased survival times in rainbow trout by about 4 months when compared with unimmunized controls. Survival time increased with both size of the fish and strength of the antigen dose.
Estimation of food consumption from field observations of fish feeding cycles
Authors: Sainsbury K. J.
Published: January 2006

The available methods of estimating food consumption by fish require that experiments be performed on confined animals and that experimental results may be validly applied to free fish. A method is described by which food consumption in periodically feeding fish may be estimated without performing laboratory experiments. A relatively simple input–output model of stomach contents is fitted to the observed time trajectory of stomach fullness, and food consumption is calculated from the estimated model parameters. Feeding is considered to be restricted to a distinct feeding period, and the rate of feeding during that period can be either constant or linearly decreased with the quantity of food already present in the stomach.

The method is applied to three examples. The model appears robust, and generally provides very similar food consumption estimates to those obtained from methods requiring an independent estimate of gastric evacuation rate. However, the described method is sensitive to violation of the assumption that feeding occurs only during a discrete feeding period.
Cannibalism in pike fry, Esox lucius L.: some experiments with fry densities
Authors: Giles N. , Wright R. M. , Nord M. E.
Published: January 2006

Pike fry were kept in 0.054‐m3 tanks at densities of 50, 100 and 150 (277, 555, 833 fry m−2) for seven weeks during which the development of social and feeding behaviour was observed. Zooplankton, macro‐invertebrates and perch fry were provided sequentially as food; the pike fry were allowed to feed ad libitum.

Zooplanktivorous fry stopped growing at 22 mm whilst, in the presence of abundant suitable alternative prey, 1–4% turned cannibalistic at 5 weeks of age; cannibals subsequently grew rapidly (mean 1.88 mm day−1). Cannibalism ensued in all tanks when the ratio of predator size: prey size was c.2:1.

Fry tended to space‐out evenly in the tanks with no overt aggression or territoriality. Behaviour was typified by remaining still for long periods, particularly subsequent to the onset of cannibalism. Cannibals were attracted by fry movements which often initiated attacks.

Daily per capita mortality rates showed no crowding effects before cannibalism but significant density‐dependent mortality due to cannibals. Consumption rates of cannibals varied between 0.63 and 6.0 fry per cannibal per day. Cannibals accounted for 54–96% of daily mortality in the experimental tanks. These results are discussed in relation to proposed mechanisms of pike population density regulation.
The immune system of juvenile thick‐lipped grey mullet, Chelon labrosus Risso: antibody responses to soluble protein antigens
Authors: Mughal M. S. , Manning M. J.
Published: January 2006

Juvenile thick‐lipped grey mullet, Chelon labrosus, believed to be about 6–7 months old, possessed well developed lymphoid organs including a clearly differentiated thymus with distinct cortical and medullary zones. However, unlike older fish, the juvenile mullet usually failed to produce antibody in response to a single injection of classical thymus‐dependent antigen (using the soluble proteins human gamma globulin or keyhole limpet haemocyanin). Prior priming of the juvenile fish with antigen was found to potentiate antibody production following challenge with a second dose of the antigen in adjuvant, priming by oral administration being equally as effective as priming by injection. Neither juvenile nor adult mullet produced any significant level of antibody against ovalbumin.

The results suggest that, despite their apparently well differentiated lymphoid organs, juvenile mullet still show a certain level of immaturity in their antibody responses to soluble proteins; also that immunization can improve their ability to respond.
The effects of intra‐ and inter‐specific competition on the distribution of stocked juvenile Atlantic salmon, Salmo salar L., in relation to depth and gradient in an upland trout, Salmo trutta L., stream
Authors: Kennedy G. J. A. , Strange C. D.
Published: January 2006

The relative effects of inter‐ and intra‐specific competition on the distribution of stocked salmon in relation to depth and gradient were investigated in an upland stream during two summer sampling periods. The stream was divided into two areas by an impassable fish barrier, and trout were removed from the upstream section prior to 2 years of salmon stocking. A small amount of trout re‐immigration to the cleared area occurred. Under sympatric conditions in the downstream section the fry of both species were significantly more abundant in shallow water, whereas the yearling and older fish tended to inhabit the deeper, slow‐flowing areas. Under near allopatric conditions in the cleared section salmon fry changed their distribution to include deeper areas, with shallow, fast‐flowing water becoming the least preferred habitat. This trend for a wide distribution of salmon fry over all the available habitat in the upstream section was maintained in the second year when parr were present but trout remained at very low densities. It was therefore concluded that high inter‐specific competition from trout was responsible for restricting the distribution of salmon fry to shallow habitat in the control area. Intra‐specific competition from older salmon apparently only affected the growth and survival of salmon fry. The regulating mechanisms involved in these inter‐ and intra‐specific effects are discussed in terms of competition for stream resources and predation. Recommendations based on the findings are made for stocking and habitat management of salmonid waters.
Scanning electron microscopy of the chorion of selected freshwater fishes
Authors: Johnson E. Z. , Werner R. G.
Published: January 2006

The external morphology of the chorion of five species of freshwater fish (Alosa pseudoharengus, Oncorhynchus kisutch, Osmerus mordax, Esox masquinongy, and Stizostedion vitreum) were studied using scanning electron microscopy. Electron micrographs and descriptions of the five species are presented. The results suggest that the surfaces are sufficiently distinct to allow for differentiation based on surface architecture at the ultrastructural level.
Seasonal changes in the physiology of brook trout, Salvelinus fontinalis (Mitchill), in a sub‐Arctic river system
Authors: Cunjak R. A. , Power G.
Published: January 2006

Brook trout, Salvelinus fontinalis, were sampled from two sites on the Koksoak River system in northern Quebec to determine seasonal physiological changes in hematology and proximate body composition. Water content increased over the winter at both sites, whereas body lipids decreased. The relationship was most pronounced in the anadromous trout of the Caniapiscau River compared with the smaller resident trout of a tributary stream. Serum protein levels decreased significantly over the winter with the greatest depletion being realized by Caniapiscau River trout. Despite the severity of the winter stream environment in the north, the extent of depletion was similar to that encountered in temperate latitudes, suggesting compensatory physiological mechanisms within the species’ latitudinal range. By mid‐summer both populations had restored their depleted energy stores, especially the anadromous trout which accumulated the greatest amount of lipids after feeding in the estuary. Serum glucose levels were maintained at high levels during the winter, then declined in the summer. Differences between the two sites for the degree of physiological change are discussed in relation to specific overwintering strategies and life history variation.
Development of eggs and larvae of the flounders Rhombosolea tapirina and Ammotretis rostratus (Pisces: Pleuronectidae)
Authors: Crawford C. M.
Published: January 2006

The stages of development of laboratory‐reared eggs and larvae of Rhombosolea tapirina and Ammotrelis rostratus are described. They both exhibited á typical pleuronectid pattern of development. At ambient seawater temperature of 11.1–13.8° C R. tapirina eggs hatched 83–93 h after fertilization and larvae metamorphosed c. 65 days later at mean length of 8.83 mm. Hatching of A. rostratus eggs occurred 93–105 h after fertilization and larvae metamorphosed after c. 69 days (mean length 11.21 mm) at 12.7–16.5° C. The two species can be readily separated by their morphology, meristics and pigmentation. In particular, the eggs differ in diameter, only R. tapirina larvae possess a pair of spines in the otic region, and juvenile A. rostratus have only a left pelvic fin.
Changes in body composition and morphology of young‐of‐the‐year gulf menhaden, Brevoortia patronus Goode, in Fourleague Bay, Louisiana
Authors: Deegan L. A.
Published: January 2006

Body composition (lipid, water, protein, energy content) and metamorphosis of young‐of‐the‐year gulf menhaden, Brevoortia patronus Goode, were examined over a yearly cycle in Fourleague Bay, Louisiana. Metamorphosis from larvae to juveniles, as indicated by the body depth to length ratio, was completed by 30 mm S.L. Analysis of the length/weight relationship indicated separate equations for larvae/postlarvae (< 30 mm S.L.) and juvenile/subadults (30–100 mm S.L.). Major body composition changes from larvae to subadult included an increase in lipid content, a corresponding increase in energy content, and a decrease in nitrogen content. Young‐of‐the‐year gulf menhaden did not exhibit the seasonal pattern of condition factors typical of adult clupeids. There may be a shift in energy allocation away from protein growth to lipid storage associated with attainment of a larger size. Initiation of emigration may be related to lipid storage and temperature change, with higher lipid content fish migrating first. End‐of‐year variations in fish size and lipid storage may be related to environmental conditions, such as water temperature and salinity.
The ecology of fish occurring in shallow water creeks of a Nigerian mangrove swamp
Authors: Wright J. M.
Published: January 2006

The population changes of nine species of fish from a mangrove swamp near Port Harcourt, Nigeria, including species of Tilapia, Sarotherodon, Aplocheilichthys, Porogobius and Yongeichthys are described. The most important factor affecting the fish populations is salinity.
Indicative value of mercury concentration in adipose fin of brown trout, Salmo trutta L.
Authors: Skurdal J. , Skogheim O. K. , Qvenild T.
Published: January 2006

Investigation of adipose fin and axial muscle mercury concentration in brown trout, Salmo trutta, from Lake Tyrifjorden, south‐east Norway showed that these were highly correlated (r= 0.93, P<0.001), but adipose fin mercury concentrations were approximately 80% lower. Analysis of adipose fin mercury concentration may prove helpful in documenting mercury contamination in aquatic environments. Conflicts regarding the highly‐priced salmonids are reduced when sampling from living individuals.
Chromosomal polymorphism associated with Robertsonian fusion in Seriola dumerili (Risso, 1810) (Pisces: Carangidae)
Authors: Vitturi R. , Mazzola A. , Macaluso M. , Catalano E.
Published: January 2006

The diploid numbers 2n= 48, and 2n= 47 have been determined for the greater amberjack, Seriola dumerili. A chromosome polymorphism due to Robertsonian fusion is present in this species. A simple sex‐determining mechanism has not been observed.
Territory dynamics and cost of reproduction in a captive population of the colonial nesting mouthbrooder Oreochromis mossambicus (Peters)
Authors: Turner G. F.
Published: January 2006

A constant population of the colonial‐nesting cichlid Oreochromis mossambicus (Peters) was maintained, over a long period, in a large aquarium tank. The larger and more dominant males more often held territories in the more sheltered areas, which were favoured by all males, and which seemed to lead to greater courtship success. The aggressive and reproductive behaviour of adult males was analysed and was, initially, found to be strongly influenced by the fishes' relative sizes. Towards the end of the study period, true size became less important in affecting such behaviour than the initial size, suggesting that there was a persistent effect of previous interactions. The initial and final sizes of males were found to be negatively correlated, suggesting that one cost of territorial reproductive behaviour is reduced growth.
Aspects of the reproductive biology of Gonostoma bathyphilum (Gonostomatidae)
Authors: Badcock J.
Published: January 2006

Protandrous hermaphroditism among deep‐sea fishes is known only within one family, Gonostomatidae, and therein restricted to a few species of two genera, Cyclothone (C. atraria, C. microdon) and Gonostoma (G. elongatum, G. gracile). Gonostoma bathyphilum, the deepest dwelling (700–2700 m depth) of Gonostoma spp., is also protandrous and shares with Cyclothone spp. an expression of sexual dimorphism manifested by the excessive development of olfactory structures, including the olfactory lobes, in ripe males. Sex‐reversal in ripe males, therefore, involves a regression of these structures. The relationships apparent between sex, maturity and olfactory development, and those between animal size, maturity and depth of occurrence, indicate that whilst protandry is an integral component of the species' reproductive strategy some individuals develop directly as females and that among males (max. size 150 mm S.L.) sex‐reversal is not obligatory. Primary females, together with those derived from prematurely reversing males, may form an early maturing female group, spawning for the first time at about 110–120 mm S.L. Most hermaphrodites were < 100 mm S.L., and within the 70–99 mm S.L. size‐range a significant proportion had mature male characters. Since males of this size were all found to be immature, this suggests that these hermaphrodites are derived from a precocious element within the initial male population, and, by virtue of size‐stratification by depth, are responsible for mating with the early‐maturing females. The lack of a marked seasonality in the sexual cycle implies an ever presence of all sexual categories within the population. It is conjectured that sex‐reversal of ripe males is a response to critical population density levels of ripe females and that the smaller, precocious males would be more prone to sex‐reversal than the larger, later‐maturing ones. In some respects protandry in G. bathyphilum is similar to that in G. elongatum. In the latter, however, the reproductive cycle is seasonally linked and sex‐reversal in males is probably obligatory. Even so, critical density levels of ripe females can still be invoked as being causal to sex‐reversal.