bluuebunny/crossref_metadata_2025 huggingface dataset:
The swimming endurance of threespine sticklebacks, Gasterosteus aculeatus L., from the Afon Rheidol, Wales
Authors: Whoriskey F. G. , Wootton R. J.
Published: January 2006

The endurance of threespine sticklebacks, Gasterosteus aculeatus, swimming with pectoral fin locomotion at 20° C in a laboratory flume was measured. Each trial lasted a maximum of 480 min. At a speed of 4 body lengths per sec (L s−1) all fish were still swimming at the end of the trial, but endurance decreased at higher speeds. At speeds of 5 or 6 L s−1 (20–30 cm s−1) a few fish still maintained labriform locomotion for the 480 min. However, at a speed of 7 L s−1 all fish furled their pectoral fins and used body and caudal fin propulsion but fatigued rapidly. During sustained swimming, fish could cover distances of 6 km or more. No significant differences between males and females were found.
The effects of food type, meal size and body weight on digestion and gastric evacuation in turbot, Scophthalmus maximus L.
Authors: Bromley P. J.
Published: January 2006

Experiments were conducted on a size range of turbot using whole prey organisms. Stomach contents were serially sampled at intervals after feeding on a range of meal sizes of sandeels and sprats. Gastric evacuation was essentially linear with time, though some fluctuations were observed. Control over evacuation appeared to be by regulation of the processes leading to chyme production. Close agreement between evacuation rate and the satiation feeding rate of fish in laboratory experiments was observed. Implications of these findings for techniques of estimating the feeding rates of natural fish populations are discussed.
Composition and ultrastructure of elasmobranch granulocytes. II. Rays (Rajiformes)
Authors: Hine P. M. , Wain J. M.
Published: January 2006

The blood granulocyte composition of seven species of ray is given together with ultrastructural observations made on the epigonal organ and blood of Pavoraja spinifera and the spleen of a deepwater rajid skate. Under the light microscope three granulocyte types, eosinophils, eosinophilic granulocytes and neutrophilic granulocytes could be distinguished. At the EM level two granulocyte types were apparent, one with elongated granules containing longitudinal fibrils that consolidated to form an axial rod‐like inclusion, and the other with large, spherical, uniformly electron‐dense granules. Correlation of light and electron microscope observations indicated that the neutrophilic granulocytes with weakly basophilic, elongated granules become weakly eosinophilic, as eosinophilic granulocytes, and these in turn develop to eosinophils with granules containing axial rods. The other granulocyte type forms another population of eosinophils with spherical granules.

The inter‐relationship of these granulocytes, the identification of eosinophilic granulocytes, or heterophils, as immature eosinophils, and the co‐existence of two morphologically distinct eosinophil forms are discussed.
The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds
Authors: Wright R. M. , Giles N.
Published: January 2006

Yolk‐sac pike fry were stocked at densities of 0.74 – 81.4 m−2 in two ponds, each divided into eight sectors (mean area 155.8 m2). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size‐range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density‐independent but switched by late June/July to density‐dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May‐July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm−2 and in Pond 2 was 3.49gm−2.

Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m−2.

Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m−2 is advised if large, density‐dependent mortalities are to be avoided.
Different populations of Scomber australasicus in New Zealand and south‐eastern Australia, demonstrated by a simple method using monogenean sclerites
Authors: Rohde K.
Published: January 2006

A simple method for distinguishing fish populations using monogenean sclerites is described. Monogeneans are left in a drop of 45% acetic acid on a microscope slide for a few minutes, and squashed under a cover slip to spread the hamuli and genital hooks in one plane. Hamuli and hooks are then measured with the aid of measuring eyepieces. Measurements of sclerites of Kuhnia and Pseudokuhnia fixed directly in 10% formalin or fixed in 10% formalin after freezing for several days gave the same results. Prerequisites for the use of the method are that monogeneans occur in sufficient numbers and show distinct geographical variation. The method is easiest to use if the size of sclerites does not change with body growth. Kuhnia scombri (Monogenea: Polyopisthocotylea) from the mackerel, Scomber australasicus, in New Zealand and New South Wales differ significantly in the length of the hamuli; it is concluded that there may be different populations of mackerel at the two localities. There also are different populations of Scomber japonicus in Japan and Ecuador, and sympatric populations of S. japonicus and S. australasicus in Japan harbour identical populations of the monogeneans Pseudokuhnia minor and Kuhnia sprostonae.
Changes in blood respiratory properties and cardiovascular function during acute exposure to hypoxic water in an air‐breathing teleost, Channa maculata
Authors: Yu K. L. , Woo N. Y. S.
Published: January 2006

Changes in blood respiratory properties and cardiovascular function of Channa maculata are described in fish acutely exposed to water of different oxygen tensions. The oxygen dissociation curve of the blood was hyperbolic, and the blood had a high oxygen affinity (P50= 7.6 mm Hg at pH = 7.6) and a large Bohr coefficient. The persistently higher blood oxygen level in the dorsal aorta compared with that in the bulbus arteriosus regardless of the ambient oxygen tensions tends to support Ishimatsu and Itazawa's (1983) suggestion that oxygenated and deoxygenated blood could be. at least partially, separated in the heart of Channa. Acute exposure to hypoxic water induced insignificant changes in blood oxygen tension and saturation. However, bradycardia, hypotension, haemodilution and antidiuresis were observed in fish exposed to severely hypoxic (PO2≤ 30 mmHg) but not to moderately hypoxic (PO2= 50 mmHg) water. These data suggested that Channa maculala possessed adaptive blood respiratory properties and blood circulation pattern to allow the fish to take up oxygen from air without significant branchial oxygen loss to the surrounding hypoxic water.
Larval development of carp, Cyprinus carpio L., in acidic water
Authors: Korwin‐Kossakowski M.
Published: January 2006

Laboratory experiments measuring survival and growth at various pH levels and two temperatures indicate that the threshold of pH of water below which larval development of carp is stopped is 5.0–5.2, the development of some individuals being stopped within the pH range 5.0–5.5. Inhibition of development is due to the inability of a larva to fill its swimbladder with air, this preventing swimming and leading to death from starvation. In water of pH 5.5–6.0 the development may be undisturbed, though slower. The effect of water acidification is reflected in slower growth rate and prolongation of the larval stages of development.
The food, feeding habits and distribution of a siluroid catfish, Bagrus docmac (Forsskal), in the Kenya waters of Lake Victoria
Authors: Okach J. O. , Dadzie S.
Published: January 2006

Adult Bagrus docmac in the Nyanza Gulf of Lake Victoria feeds mostly on fish–Haplochromis spp. and Engraulicypris argenteus (Pelligrin). Juveniles prefer aquatic benthic invertebrates with Phyllogomphus aethiop.?(K.elys), Phanostoma senegalense(Brauer), Chironomus spp. and Caridina nilotica (Roux) dominating, followed by Chaoborus spp., Povilla adusla (Navas), Valvata spp. and Neoperla spio (Newman) in order of importance. B. docmac exhibits diurnal changes in feeding habits. It feeds actively during dusk and dawn, taking advantage of the twilight environment for successful feeding mission–a crespuscular feeding behaviour. Selectivity of food seems dependent on occurrence of prey items. The species has an ubiquitous distribution in the Gulf but occurs more frequently with increasing water depth and decreasing water temperature. The biomass of the predator shows little correlation with water conductivity. Bagrus docmac and the other important piscivorous species in the lake, Lates niloticus (L.), are mutually exclusive in their bathymetric distribution within the Gulf. They also have different preferences for water temperature and conductivity.
The stress‐response of rainbow trout to experimental infection with the blood parasite Cryptobia salmositica Katz, 1951
Authors: Laidley C. W. , Woo P. T. K. , Leatherland J. F.
Published: January 2006

Physiological responses of rainbow trout, Salmo gairdneri Richardson, to experimental infection with the blood haemoflagellate Cryptobia salmositica were monitored for 7 weeks to determine whether the parasitaemia elicited a classical stress‐response as evidenced by elevated plasma cortisol and glucose levels. There was a progressive anaemia, hepatomegaly, splenomegaly, and depressed plasma T3, T4, protein and glucose concentration, and lowered liver glycogen content in the parasitized fish throughout the study, which clearly indicated that the animals were under physiological duress. Moreover, these hormonal and metabolic indicators showed no indication of recovery with the decline in blood parasite numbers. However, there were no differences in plasma cortisol or glucose levels between infected and control fish throughout the study, suggesting that the parasitaemia did not activate the pituitary‐interrenal axis.
Preparation of chromosomes from early stages of fish for cytogenetic analysis
Authors: Baksi S. M. , Means J. C.
Published: January 2006

Techniques previously used to prepare tissues of adult fish for cytogenic analysis were modified in order to obtain large numbers of well‐spread metaphases from eggs and larvae. This method was applied successfully in genotoxicity studies of early life stages of Cyprinodon variegatus and Morone saxatilis.
X‐cells in the gills of an Antarctic teleost, Pagothenia borchgrevinki
Authors: Franklin C. E. , Davison W.
Published: January 2006

X‐cell tumours have been described previously from teleost fish of the Northern Hemisphere, in which they occurred as lesions of the skin, pseudobranchs or gills. The present study describes X‐cell tumours from the gills of an Antarctic teleost, Pagothenia borchgrevinki, thus extending the range to the Antarctic and also the Southern Hemisphere. Gills of affected fish were distinctly swollen and white in appearance, indicating that the gills were not functional as gas exchange organs. The affected gill tissue contained large numbers of X‐cells, large spherical cells with a distinct extracellular coat and many densely staining membrane‐bound granules. The possible origin of the cells is discussed.
The effects of testosterone implants on ovarian morphology in the bluehead wrasse, Thalassoma bifasciatum (Bloch) (Teleostei: Labridae)
Authors: Kramer C. R. , Koulish S. , Bertacchi P. L.
Published: January 2006

The effects of exogenous testosterone pellet implants at 21 and 40 days on the ovary of Thalassoma bifasciatum, a protogynous marine fish, are described. The characteristic markings of the terminal blue phase appeared by 4 to 5 days and were complete by 18 days. There was no shift in sex ratio in the treated fish when compared to an untreated control group. None of the ovaries showed signs of precocious transformation, i.e., spermatogenic tissue was lacking, and there was no evidence of duct formation. Instead, however, the ovaries of the treated fish showed marked degenerative changes characterized by oocyte breakdown, fat infiltration, vacuolization, the accumulation of fibrous PAS+ material and the appearance of small eosinophilic cells.

These findings conflict with earlier studies on the same organism that employed different procedures. However, they resemble more closely the results obtained from work on another protogynoid, the ricefield eel, Monopterus albus. They add new light on the role of sex hormones in the reversal process of T. bifasciatum and hermaphroditic fishes in general.
Downstream migration and critical water velocities in stream channels for fry of four salmonid species
Authors: Heggenes J. , Traaen T.
Published: January 2006

Fry of brown trout, Atlantic salmon, brook trout and lake trout were tested for downstream migration and critical velocities with a method of stepwise increasing water velocities. Each velocity was tested for 15 min before increase to the next step. Critical velocities for fry entering the free‐feeding stage, defined as the stage when the fry has resorbed its yolk sac and will have to ascend from the bottom gravel to catch food, were between 0.10 and 0.25 m s−1, varying among individuals and depending on species and water temperature. Downstream displacement started at lower velocities. Lake trout had the lowest critical velocity. Temperature influenced swimming performance considerably. On average, a 7°C increase in temperature resulted in a 0.05 m s−1 increase in critical velocity. The fry actively searched out the low‐velocity niches in the channels. Flow‐sensivity gradually decreases with fry development; when the fry had reached a length of 40–50 mm they were able to tolerate water velocities higher than 0.50 m s−1.
The effect of hunger, shoal size and the presence of a predator on shoal cohesiveness in bluntnose minnows, Pimephales notatus Rafinesque
Authors: Morgan M. J.
Published: January 2006

Shoals of fish vary in their degree of cohesiveness as certain conditions such as hunger, predation risk and shoal size vary: this study relates this variation to the benefits of shoaling. Shoals of bluntnose minnows, Pimephales notatus Rafinesque, consisting of different numbers of individuals were starved for 5, 24 or 72 h and allowed to forage in the presence or absence of a predator. Cohesiveness was measured as the dispersion offish within the shoal (the radius of the longest axis of the shoal corrected for the number of fish in the shoal), straggle frequency (the number of movements by individuals of at least 5 body lengths away from the shoal) and aggressive interactions between shoal members. Cohesiveness increased as shoal size and the benefits per individual increased. Cohesiveness also increased in the presence of a predator, as did the importance of shoaling as a means of reducing predation risk. Cohesivenes decreased as hunger level increased, possibly as a result of increased competition for food among shoal members.
The effect of antimicrobial compounds on the gastrointestinal microflora of rainbow trout, Salmo gairdneri Richardson
Authors: Austin B. , Al‐Zahrani A. M. J.
Published: January 2006

Populations of aerobic and anaerobic heterotrophic bacteria occurring in the gastrointestinal tract of healthy rainbow trout were estimated using a dilution plate technique. Data revealed a progressive decline in numbers of aerobic bacteria along the digestive tract from oesophagus to lower intestine. However, the highest numbers were recovered from the intestinal contents and faeces. Anaerobes were generally restricted to the upper intestine and intestinal contents. The aerobic component of the bacterial microflora from the digestive tract was equated with Acinetobacter calcoaceticus, Aeromonas hydrophila, Bacillus circulans, Bac. megaterium, coryneforms, Grampositive irregularly shaped rods, Flavobacterium sp., Kurthia sp., Microhacterium sp., Providencia stuartii, Pseudomonas spp., Ps.fluorescens and Ps. pseudoalcaligenes. Evidence from scanning electron microscopy pointed to a general lack of colonization of the gut wall: instead, microorganisms were abundant in the intestinal contents. Antimicrobial compounds, i.e. oxolinic acid, oxytetracycline and sulphafurazole (which are commonly used to combat infections by Gramnegative bacterial fish pathogens), caused an increase in bacterial numbers throughout the digestive tract, with maximal numbers in the lower intestine. The bacteria, comprising an essentially different range of taxa, were generally resistant to the antibiotics in use. Conversely, erythromycin and penicillin G, which are used to treat some diseases caused by Gram‐positive bacteria, caused a rapid reduction in bacterial numbers within the gastrointestinal tract.
The apparent lack of effect of supplementary dietary zinc on zinc metabolism and metallothionein concentrations in the turbot, Scophthalmus maximus (Linnaeus)
Authors: Overnell J. , Fletcher T. C. , McIntosh R.
Published: January 2006

Turbot were fed either a basal diet containing approximately 100 mg zinc kg−1 or a similar diet supplemented with 1000 mg kg−1; the fish were sampled over a period of 220 days. At final sampling there was no significant difference between control and test animals in hepatic and renal metallothionein levels, hepatic and renal zinc levels and white muscle, skin and bone zinc concentrations.
Emergence of Baltic salmon, Salmo salar L., in relation to temperature: a laboratory study
Authors: Brännäs E.
Published: January 2006

Emergence pattern and developmental status at emergence of Baltic salmon fry from the Umeälven hatchery stock (63°50′N, 20°25′E) were studied at 6, 10 and 12°C in the laboratory. The number of days and degree days from hatching to 50% emergence decreased exponentially with increasing temperature. Synchronization of emergence increased with temperature. Optimal temperature for incubation of yolk‐sac alevins was 10°C, which resulted in the largest fry at emergence and the lowest death rate. Fry kept at 6°C had the lowest mean weight and at 12°C the highest death rate. The fry emerged at an earlier developmental state with more yolk at 12°C than at 6°C. The Baltic salmon had a faster developmental rate during the gravel‐phase, as compared to more southern Atlantic salmon populations.
Aspects of the reproductive biology of the bass, Dicentrarchus labrax L. I. An histological and histochemical study of oocyte development
Authors: Mayer I. , Shackley S. E. , Ryland J. S.
Published: January 2006

Histological and histochemical studies of oocyte development in the bass, Dicentrarchus labrax L., showed that three types of inclusions are formed during vitellogenesis. Lipid yolk accumulates first as lipid droplets, followed by protein yolk in the form of discrete protein yolk granules. The third type of inclusion are the small cortical alveoli (intravesicular yolk/yolk vesicles, i.e.‘carbohydrate yolk’) which form in the peripheral cytoplasm after both the lipid and protein yolk have started to accumulate. While the protein yolk granules maintain their structural integrity through to maturation, forming a densely packed zone in the mid‐outer cortex, the lipid yolk droplets continually coalesce and migrate centripetally, forming a prominent zone of large lipid droplets in the inner‐mid cortex. From the histological study of oocyte development, a number of distinct developmental stages are delineated, while gross examination of the paired ovary revealed that, depending on its stage of development, it can be placed into one of seven maturity stages.
Diel feeding periodicity, daily ration and prey selection of a riverine population of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)
Authors: Sagar P. M. , Glova G. J.
Published: January 2006

The diel feeding periodicity, daily ration and prey selection of juvenile chinook salmon, Oncorhynchus tshawytscha, were studied in relation to the available prey. Maximum dry weight of food intake occurred about dawn, when mayflies were the major prey, but the greatest number of freshly eaten prey occurred during the afternoon, when chironomids and terrestrial dipterans predominated. Feeding activity at night was low, with smaller mayflies comprising up to 50% of the prey. During the day the young salmon fed selectively on chironomids and the larger mayflies, while trichopterans and terrestrial taxa were under‐represented in the diet. Food consumption over the 24‐h period averaged 8.3% of the fish dry body weight. Prey abundance in the drift explained about 50% of the composition of the diet. Although the fish selected larger mayflies, size apparently was not a main criterion for selection because chironomids, although smaller than mayflies, were also frequently eaten. Previous dietary experience of the fish and the diel pattern of prey abundance appear to best explain the selective feeding of juvenile chinook salmon.
Chromosome numbers, genome sizes, cell volumes and evolution of snake‐head fish (family Channidae)
Authors: Banerjee S. K. , Misra K. K. , Banerjee S. , Ray‐Chaudhuri S. P.
Published: January 2006

Chromosome number, C‐value and cell volume studies were carried out on three species of the genus Channa, viz., C. punctatus, C. striatus and C. gachua. The chromosome number, karyotypic structure and DNA content per cell along with cell volume are reported and described. A series of chromosomal rearrangements are established in three different karyotypes along with polyploidy. Both pericentric inversion and Robertsonian fusion played a major role in chromosome rearrangements. The nuclear DNA content of these three species is within 19‐29% of the present‐day placental mammals, and is thus lower than the median amount for fishes in general and teleosts in particular. Their lower DNA content suggests that the three species of the family Channidae are highly specialized, and this is supported by their known morphologic, reproductive, behavioural and ecological characteristics.

The evolutionary significance of these chromosomal rearrangements, their origin and their mode of establishment are discussed. A probable phylogenetic model based on karyotype, C‐value and chromosomal rearrangements of the genus is presented.
Effect of a sprint training protocol on growth rate, conversion efficiency, food consumption and body composition of rainbow trout, Salmo gairdneri Richardson
Authors: Gamperl A. K. , Bryant J. , Stevens E. D.
Published: January 2006

Rainbow trout were sprint‐trained (30 s duration) once or twice on alternate days for a period of 6 weeks. Swim speed for the first 10 s of a training bout averaged 11.4 bls for group 2 (trained once) and 10.2 bl s −1 for group 3 (trained twice). Food consumption, growth rate and conversion efficiency were measured over 2‐week periods. Food consumption was 31‐38% less for the trained groups than for the control group (group 1). The growth rates of control and trained fish increased gradually over the training period. The growth rate of trained fish was always significantly less (48‐81%) than that of control fish. Although conversion efficiency was significantly less for group 3 at the beginning of training, no other significant differences in conversion efficiency were recorded. Maintenance rations were high in the initial period for all groups, but were lower than the initial values in the second and third periods. While condition factor was significantly lower for the trained groups, there were no differences in percent tissue protein, lipid, or moisture.
Effect of mink, Mustela vison Schreber, predation on cohorts of juvenile Atlantic salmon, Salmo salar L., and brown trout, S. trutta L., in three small streams
Authors: Heggenes J. , Borgstrøm R.
Published: January 2006

Two cohorts of Atlantic salmon parr and one of brown trout were studied in periods with and without the presence of mink, Mustela vison. In all localities a marked increase in mortality rate was observed during periods when mink were present. Mink were observed catching salmon parr, and approximately 10% of the parr had bite marks, especially on the tail fins. In the smallest stream with brown trout, the mortality rate was 0.80 during a few days with mink present; remnants of trout were found along the stream. The present study suggests that mink predation may be a major cause of mortality of salmonids in small streams. The results indicate that predation efficiency may vary with characteristics of the habitat, especially stream width and discharge, and fish density.
The importance of estuaries for sea‐bass, Dicentrarchus labrax (L.)
Authors: Kelley D. F.
Published: January 2006

Information on estuary‐dependence of bass in U.K. waters is summarized from recent published reports and some unpublished data.

There is substantial reliance on estuaries (including tidal backwaters with little freshwater inflow) such as the Hampshire harbours, in the first 4–5 years of life. Man‐related hazards to survival are considerable and increasing: they include destruction of or damage to habitats, losses of 0‐groups in power‐station intakes, and excessive unregulated fishing effort, mainly on 4–5‐year‐old bass. Some measures to protect bass in estuaries are now in hand, but much remains to be done.
Seasonal biomass and diversity of estuarine fishes coupled with tropical habitat heterogeneity (southern Gulf of Mexico)
Authors: Yåñez‐Arancibia A. , Lara‐Dominguez A. L. , Rojas‐Galaviz J. L. , Sånchez‐Gil P. , Day J. W. , Madden C. J.
Published: January 2006

Nekton dynamics were studied in two contrasting habitats in Terminos Lagoon, Mexico. Over an annual cycle, a total of 83 fish species used the high‐salinity fringing mangrove/Thalassia testudinum habitat and biomass ranged from 0.43 to 3.43 g m−2. The highest biomass occurred during the dry season when aquatic primary production was highest (i.e. 333 g C m−2 year−1). By contrast, 65 species used the freshwater and low‐salinity riverine mangrove/Crassostrea virginica/Vallisneria habitat and biomass ranged from 0.57 to 1.48 g m−2 with the highest biomass occurring during the wet season, the time of highest primary production in this habitat (i.e. 219 g C m−2 year−1). The high‐ and low‐salinity habitats serve as ecological bridges between freshwater areas and the sea. Fish life histories have evolved to utilize these habitats for spawning, feeding and nursery grounds in a manner which generally leads to the use of different habitats during the periods of highest primary productivity.
Bioenergetics of growth of a cyprinid, Phoxinus phoxinm (L.): development and testing of a growth model
Authors: Cui Y. , Wootton R. J.
Published: January 2006

The development, verification and validation of a bioenergetics growth model for the European minnow, Phoxinus phoxinus, are described. Sensitivity analysis showed that the growth predicted by the model was sensitive to parameters used in the estimates of the energy and dry matter content of the fish and metabolic rate. The model gave good predictions of the form of the growth‐temperature relationship, but failed to predict the growth‐ration relationship well. Validation of the model against experimental data showed that the model underestimated growth at lower rations and overestimated growth at higher rations. Only at low ration levels did the model predict growth rates equivalent to those recorded for a natural population of minnows. Analyses of an empirical regression equation for growth rate, as well as the bioenergetics model, highlighted four areas for future research: (1) the energy content of fish in relation to environmental factors; (2) the feeding metabolism of fish in relation to environmental factors; (3) the regulatory mechanism of long‐term growth; (4) the effect of gonadal maturation on long‐term growth. The identification of these problems illustrates the advantage of a partially explanatory model, the bioenergetics model, over a descriptive empirical model.
Changes in plasma thyroid hormone levels in pink salmon, Oncorhynchus gorbuscha, during their spawning migration in the Fraser River (Canada)
Authors: Leatherland J. F. , Down N. E. , Donaldson E. M. , Dye H. M.
Published: January 2006

Plasma thyroid hormone levels were measured in pink salmon, Oncorhynchus gorbuscha, during their spawning migration in the Fraser River, British Columbia. The plasma levels of both l‐thyroxine (T4) and triiodo‐l‐thyronine (T3) were significantly higher in males than in females. In both sexes the hormone levels were maintained, or increased somewhat, during the early stages of migration, but fell thereafter. In females the plasma T4 and T3 levels of salmon collected on the spawning grounds were at or below detectable levels of the assays. The changes in thyroid hormone levels are correlated with changes in plasma insulin, gonadotropin, gonadal steroid hormones, cortisol and vitellogenin levels measured in the same specimens.
Differential effects of low pH and aluminium on the caudal neurosecretory system of the brook trout, Salvelinus fontinalis
Authors: Hontela A. , Roy Y. , van Collie R. , Lederis K. , Chevalier G.
Published: January 2006

Brook trout were subjected to soft water at pH 6·5, 5·5 or 5·0 without aluminium added, or to water at pH 5·5 with 200,300 or 500 μg Al I‐1 added. The response of the caudal neurosecretory system to low pH or aluminium was evaluated after one week by measuring the urotensin I and urotensin II concentrations in the urophysis by radioimmunoassay, and by morphometric analysis of the caudal neurosecretory cells. A positive correlation was found between urotensin I concentrations and acidity, and a negative correlation was found between urotensin II concentrations and total aluminium in the water. Morphometric indices (cell size and proportion of lobed nuclei in the caudal neurosecretory cells) suggested increased synthetic activity in the caudal neurosecretory cells of fish at pH 5·5 compared to pH 6·5.
Annual variation in energy reserves in male three‐spined stickleback, Gasterosteus aculeatm L. (Pisces, Gasterosteidae)
Authors: Chellappa S. , Huntingford F. A. , Strang R. H. C. , Thomson R. Y.
Published: January 2006

Wet and dry weights of tissue were measured and concentrations of glycogen, lipid and protein were estimated for the liver, gonad and carcass of male sticklebacks from an annual population collected each month over one complete year. In young‐of‐the‐year there is one period of rapid weight gain, in all three body regions (liver, carcass and gonads) but particularly of the carcass, in the autumn and a second in spring and early summer. This is accompanied by an increase in the water content of all three body regions. The gonadosomatic index also increases sharply in spring and early summer. Young sticklebacks accumulate lipid and glycogen slowly during the autumn and winter of their first year of life and more rapidly from late winter to early summer. Thus, the period of most rapid accumulation of these reserves coincides with the time when body weight and gonad maturation are also increasing sharply. Lipid and glycogen levels fall during the reproductive season in those males that breed, so that by July they are reduced to 43% and 37% (respectively) of their peak values in May. Levels of protein increase throughout the year as the fish grow, but in breeding males by July the concentration of protein in the carcass falls to 70% of pre‐breeding levels. Breeding males therefore reach the end of the reproductive season with their total energy reserves severely reduced, and consequently they suffer a very high mortality. In contrast, adult males that fail to reproduce survive beyond the breeding season. They continue to gain weight and to accumulate lipid and glycogen from August to September, but these energy reserves fall (to levels comparable to those of post‐breeding fish) in December, when these fish probably die. These results demonstrate that in male sticklebacks, growth and gonad maturation can be sustained in parallel with the accumulation of energy reserves, which are subsequently extensively depleted as a result of reproductive activities.
Routine metabolism of juvenile spot, Leiostomus xanthums (Lacépède), as a function of temperature, salinity and weight
Authors: Moser M. L. , Hettler† W. F.
Published: January 2006

Routine oxygen consumption rates of juvenile spot, Leiostomus xanthums, were measured over a range of temperatures, salinities and fish weights. As predicted, QO2 increased with temperature and decreased with body weight. However, QO2 decreased with decreasing salinity and did not show the expected minimum at isosmotic concentrations. The data are best described by the relationship: log10QO2 (mg O2 g−1 h−1) = 0.129 loglo salinity (%0) + 1.604 log10 temperature (°C)‐0.1401og10(g)‐2.767.
Chromosomal and morphological analysis of two populations of Salmo trutta sbp. fario employed in repopulation
Authors: Mořan P. , Pendás A. M. , García‐Vázquez E. , Linde A. R.
Published: January 2006

Two stocks of brown trout employed in repopulating the rivers of Asturias (northern Spain) were morphologically and karyotypically analysed. Both stocks were significantly different. The foreign stock was less adequate for repopulation than the autochthonous stock.
Comparative morphology and ecomorphology of the gut in European cyprinids (Telostei)
Authors: Junger H. , Kotrschal K. , Goldschmid A.
Published: January 2006

The patterns of coiling of the gut were compared in 22 species of Eurasian Cyprinidae. In selected species, also the length of gut and mucosal surface structure were compared. Piscivorous (Aspius aspius), planktivorous (Abramis ballerus) fishes as well as species feeding mainly on plankton and wind‐borne‘ drift’(Alburnus alhurnus, Pelecus cultratus) have the relatively shortest guts, with only a single loop. The same simple arrangement of a short gut is present in many euryphagous species with more or less carnivorous tendencies (Abramis sapa, Alburnoides bipunctalus, Abramis brama, Blicca bjoerkna, Chalcalburnus chalcoides memo, Gobio gobio, Leuciscus cephalus, Leuciscus leuciscus, Rutilus rutilus, Scardinius erythrophthalmus. Tinea tinea, Vimba vimba). Some benthivorous winnowers (oropharyngeal sorters) and species with herbivorous feeding tendencies have relatively long guts showing a more complex pattern of loops and coils (Barbus barbus, Carassius carassius, Chondrostoma nasus, Ctenopharyngodon idella, Cyprinus carpio). The goldfish, Carassius auratus, has the most complex coils. Scanning electron microscopy of the mucosal surface revealed five types of folding in the intestinal bulb which were only loosely related to feeding: 1, smooth surface (Aspius aspius, Leuciscus cephalus, Vimba vimba); 2, irregularly branching folds (Alhurnus alburnus, Barbus barbus, Blicca bjoerkna, Chalcalburnus chalcoides memo, Leuciscus leuciscus, Rutilus rutilus, Scardinius erythrophthalmus); 3, curl‐like folds (Tinea tinea); 4, net‐like folding pattern (Abramis brama); 5, honeycomb‐like mucosal structure (Cyprinus carpio).
Comparative pathology of some monogenean and copepod ectoparasites on the gills of Acanthopagrus australis (family Sparidae)
Authors: Roubal F. R.
Published: January 2006

The monogenean Haliotrema spariensis was associated with several foci of hyperplastic epithelium and varying amounts of cellular infiltration resulting from attachment by hamuli penetrating the lamellar blood vessels and, presumably, from feeding. Lamellodiscus major was associated with fewer but larger foci containing more extensive infiltration, suggesting a more sessile habit. The copepod Dermoergasilus acanthopagri encircled the filament with its second antenna, occluded arteries and compressed the epithelium, resulting in hyperplasia, oedema and infiltration. Ergasilus lizae inserted its second antennae into the epithelium and subepithelial region and was associated with a localized proliferative response occasionally fusing adjacent filaments. The large copepod Lernanthropus atrox caused tissue disruption, hyperplasia, haemorrhage, oedema and infiltration. Hyperplastic epithelial cells had a rounded nucleus containing variable amounts of heterochromatin, dilated organelles, deposits of glycogen‐like particles, cyoplasmic vesicles and vacuoles. Oedematous epithelial cells were less altered. Degenerating chloride cells were present in both oedematous and proliferated epithelia.
Oogenesis in cod, Gadus morhua L., studied by light and electron microscopy
Authors: Kjesbu O. S. , Kryvi H.
Published: January 2006

The development of the oocytes in the cod, Gadus morhua L., is described by light and transmission electron microscopy. The oocyte volume increases about 700 times during the stages preceding hydration. The size of the nucleoli increases 35‐fold, the cortical alveoli increase 6‐fold and the yolk granules increase 70‐fold as the oocyte grows. The maximal number of yolk granules is nearly 100000 per oocyte; this number is reduced to less than the half prior to hydration. A significant reduction occurs also in the number of nucleoli at that time. The number of cortical alveoli increases steadily towards hydration. Yolk is deposited in the oocyte as crystalline granules. The lattice is broken down at hydration, leaving the egg transparent. Follicle cells go through a primordial stage and later change to a squamous and to a cuboids shape. The presence of lipid droplets in their interior and the virtual lack of interfollicular spaces are characteristic. The chorion grows to a tripartite structure: an outer thin porous layer, an intermediate homogenous layer and an inner thick helicoidally layer. A mucous substance covers the porous layer. The occurrence of the so‐called lamellae in the helicoidal layer is considered a function of the orientation of its micro fibrils and the plane of sectioning, i.e., not caused by alternating chemical arrangements.
The feeding selectivity of silver carp, Hypophthalmichthys molitrix Val.
Authors: Smith D. W.
Published: January 2006

Effects of particle size, fish size and temperature on the filtration rate of silver carp were determined. When feeding at 20°C on zooplankton and spherical particles (yeast, micronic beads and pollen), 32‐g silver carp filter particles larger than 70 urn at a maximum rate of 18.251 h−1. For particles smaller than 70 μm, filtration rates decrease with decreasing particle size until there is no measured filtration for particles smaller than 10 μm. Filtering rates (FR) for particles between 10 and 50 μm are described by the equation, FR=−20.8 + 21.7 × log particle diameter. Filtration rates rise as fish size, particle size and temperature increase. Filtration rates per unit biomass, however, fall as fish size increases: FR= 1.54 W0.713, where FR is the maximum filtration rate in 1 h 1 fish 1 and W is weight of fish in grammes. The results of these trials are consistent with the hypothesis that particle selection by silver carp is a mechanical, passive function of gill raker morphology.
Effects of dietary fibre on the intestinal absorption of dextrin, blood sugar level and growth of tilapia, Oreochromis niloticm × O. aureus
Authors: Shiau S. Y. , Kwok C. C. , Chen C. J. , Hong H. T. , Hsieh H. B.
Published: January 2006

The roles of five different dietary fibres (cellulose, agar, guar gum, carrageenan and carboxy‐methylcellulose) each as 10% wt/wt added into the diet, affecting the intestinal sugar absorption, blood sugar level and utilization of dextrin were studied in hybrid tilapia, Oreochromis niloticus × O. aureus; dextrin and glucose were also included in the study as controls for comparison. There were seven dietary groups: each diet was fed to three aquaria each containing 15 fish. The experiment was carried out in a closed circulation, filtered, rearing system for 2 months. The results indicated that the weight gain percentage and food conversion ratio were significantly (P<0.05) lower in tilapia fed fibre‐containing diets than those of tilapia fed dextrin or glucose diet. The intestinal absorption of carbohydrate and the blood sugar content of tilapia were low when diets contained fibre, regardless of the source.
The feeding relationships of the larger fish species in a Scottish sea loch
Authors: Hall S. J. , Raffaelli D. , Basford D. J. , Robertson M. R. , Fryer R.
Published: January 2006

Patterns within a fish assemblage have been examined from catches obtained over a period of 17 months using fixed nets and rod and line sampling. A total of 19 species were caught with summer samples dominated by dab and saithe and winter samples by whiting. Cod were caught regularly throughout the year. Catches at the study site of dab and whiting occurred mainly at night but for cod and saithe catches occurred throughout the day. There was no indication ofa crepuscular or tidal rhythm for any species. Differences between our own observations and those from other published studies lead us to conclude that no species‐specific generalizations about feeding periodicities can be made. Feeding patterns are more likely to be determined by site‐specific features of particular habitats and their associated prey and predator assemblages.

Examination of stomach contents data using a variety of methods indicates that conclusions are highly dependent on the form of the resource matrix used. However, our analyses indicate that during summer cod and dab feed on a much narrower range of prey than saithe and that there is significant overlap in their diets if a resource matrix based on percentage occurrence of prey species is used. Nevertheless, most diet overlap values for the species examined were low (between 0.1 and 0.2) suggesting that competition for food is unlikely. To date, no experiments have been performed to test the hypothesis that cod and dab compete for food.
X‐ray measurements of gill‐arch movements in filter‐feeding bream, Abramis brama (Cyprinidae)
Authors: Hoogenboezem W. , Sibbing F. A. , Osse J. W. M. , v.d. Boogaart J. G. M. , Lammens E. H. R. R. , Terlouw A.
Published: January 2006

The technique of X‐ray cinematography was used to study pharyngeal movements in Abramis brama (L.). The theoretical and practical problems in X‐ray cinematography of feeding fish are discussed, as well as criteria for the selection of images suited for detailed measurements.

Respiration and filter‐feeding on Daphnia pulex (length c. 1 mm) show different gill arch movement patterns in bream. Slits between gill‐arches are kept smaller during filter‐feeding. In addition, during filter‐feeding, this inter‐arch distance decreases considerably in a posterior direction. The hypothesis that particle retention occurs on the slits formed between adjacent gillarches and their gill‐rakers is not supported by the present results.
The influence of grass carp on habitat structure and its subsequent effect on the diet of tench
Authors: Petridis D.
Published: January 2006

Ecological studies were carried out in shallow experimental sites in the Lancaster Canal to evaluate potential interactions between grass carp and feeding habits of tench.

Grass carp, through moderate weed consumption, produced better conditions for the exploitation of benthic organisms by the benthophagous tench, because tench (>35 cm fork length) were able to search for food in the open areas created. This also enabled the fish to make use of zooplankton, mainly the large species Eurycercus lamellatus whose restricted phytophilic habitat made it vulnerable to predation. Epibenthic animals, in particular gastropods and Asellus aquaticus, suffered principally from the predation, which caused severe reduction of them in the site totally depleted of vegetation. In this site, tench utilized a diet in which red chironomids were the dominant prey group together with a large amount of fine detritus.

It is suggested that a moderate control of vegetation in temperate climates, using the grass carp as the biological agent, could be a satisfactory management technique for the improvement of aquatic habitats.
Gustatory sensitivity of the herbivore Tilapia zillii to amino acids
Authors: Johnsen P. B. , Zhou H. , Adams M. A.
Published: January 2006

The gustatory sensitivity of the herbivorous fish Tilapia zillii was investigated using electrophysiological techniques. Integrated responses from facial taste nerves were recorded during stimulation by l l amino acids. All compounds proved to be effective stimuli. The relative stimulatory efficacy (RSE) determined at 1 × 10 −3 m indicated that stimuli can be organized into three groups on the basis of similarity of efficacy. Effects of pH which altered the RSE of some amino acids are documented. Amino acid RSE differed to some extent from those of previously studied carnivorous fish. There was concordance between the composition of preferred food, effective feeding stimuli and the peripheral receptor responses. These observations support the hypothesis that peripheral chemosensitivity might serve as a mechanism of feeding specialization in some fish.
Recruitment mechanism of the eel, Anguilla japonica, to the Japanese coast
Authors: Tukamoto K.
Published: January 2006

A total of 149 Anguilla japonica elvers collected at 10 locations along the Japanese coast were aged according to otolith daily increments. The interrelationships among age, birth date, body size, pigmentation stage, sampling location and the timing of recruitment were examined in order to determine the recruitment mechanism of elvers to coastal waters.

First catches of eels were earlier in the locations at lower latitudes. Age at recruitment was roughly constant, 218 ± 29 (mean ± s.d.) days old, disregarding the localities, but a weak positive correlation was obtained between age and sampling date or timing of recruitment. Body length at recruitment was also constant, 56.3 ± 2.3 mm s.l., and showed no significant correlation with either locality or recruitment timing. Estimated birth date ranged from April to November, the mean ± s.d. being 22 July 1982 ± 42 days, suggesting a peak season spawning in summer. Birth date was closely related with both the latitude of location and sampling time. Pigmentation developed more at lower latitude. Recruitment mechanism of the Japanese eel was summarized as follows: the earlier‐born individual recruits earlier at lower latitude and at younger age, but at a constant body size.
Shifts in the microhabitat of larval and juvenile roach, Rutilus rutilus (L.), in a floodplain channel
Authors: Copp G. H.
Published: January 2006

The microhabitat of roach larvae (stages L1–L6) and 0+ juveniles was examined in a braided channel (Ilon) of the Upper Rhone River, France, from weekly samples (spring‐autumn 1985) using Point Abundance Sampling by electrofishing. During early development, microhabitat exploitation was characterized by two transitions: the first at larval step L3, when morphological and physiological attributes permit the active choice of microhabitat; the second at the end of the larval and start of the juvenile period. At larval step L3, and up to L5, roach were strongly associated with lentic waters of medium depth (0.5–1.0m) and with either macrophytes or ligneous debris. The L6 and 0+ juveniles were found more often than expected in shallower waters (< 0.2m, 0.2–0.5 m) and were no longer associated with dense vegetation or ligneous debris. However, both larval (L3–L6) and 0+ juvenile roach preferred silty sand and/or silted gravel, and a lack of current. This shift, from moderately deep waters with vegetation and/or branches as larvae to open shallow waters as juveniles, demonstrates the young roach's perception and response to environmental change, with shallows exploited as a refuge from predation when protective structures become scarce or unavailable.