bluuebunny/crossref_metadata_2025 huggingface dataset:
Histopathology of Ichthyophthirim multifiliis infections in fishes
Authors: Ventura M. T. , Paperna I.
Published: January 2006

Histopathological changes involved in Ichthyophthirius multifiliis infections are described from a wide range of host fishes—carp, crucian carp hydrids, Carassius carassius×C. auralus, goldfish, eels, African catfish, Glorias lazera, several species of cichlid fishes and rainbow trout. Fish were obtained from diverse geographical regions: Israel, South Africa, Portugal and Venezuela, as well as from laboratory experimental infections. Observed histopathological changes could not demonstrate any interspecific differences, but individual fish or different groups of fish of the same species demonstrated wide variability in susceptibility to infection and consequently in the nature and severity of the histopathological response. Low to moderate primary infection and secondary reinfestations did not induce significant histopathological changes in the integument. The proliferative response of the integumentary epithelium appeared only following subsequent infections. Repeated heavy reinfections induced massive cellular necrosis and in very heavy infections extensive lysis of the epithelial tissue. Host‐parasite interactions in the light of the histological findings are discussed.
Observations on the morphology, ecology, and behaviour of Bathylychnops exilis Cohen
Authors: Stein D. L. , Bond C. E.
Published: January 2006

Bathylychnops exilis is an unusual north‐eastern Pacific mesopelagic fish of which adults have previously been undescribed and the biology is poorly known. Its sensory and digestive systems are highly modified. Sensory modifications include the equivalent of four functional eyes, well developed nasal rosettes, and lateral line canals up to 4 mm in diameter. Digestive adaptations include a peculiar mouth, large tongue, crumenal organ, and a large caecal stomach. Bathylychnops exilis apparently lacks an anal light organ. Ontogenetic changes occur in the morphology of the head, eyes, body, and coloration. Bathylychnops exilis eats crustaceans and may be medusae and microscopic organisms. Reproduction probably occurs in late summer. Adults occur most commonly at about 500 m depth, possibly in groups, and may be diurnal vertical migrators.
Some aspects of the reproductive biology of Spratelloides gracilis (Schlegel) in the Ysabel Passage, Papua New Guinea
Authors: Dalzell P.
Published: January 2006

Fecundity, length at first spawning, spawning seasonality and ovarian development of Spratelloides gracilis were determined by examining preserved ovaries from fish captured over a 5‐year period. Fecundity (F) was estimated from the number of eggs in the most advanced ovarian mode and was related to fish length (L) by the function: logeF=3.764 logeL‐7.308, and to weight (W) by: logeW= 1.210 logeW+7.337. Spawning was observed in most months of the year without any recognizable pattern between the years. Ova diameter frequencies were bimodal but the smaller mode remained stationary regardless of the position of the larger mode. This was interpreted as evidence that individual fish may spawn only once. From data on egg length versus fish length and gonad index versus fish length it was estimated that fish were first capable of spawning at 45 mm (fork length).
Temperature comparisons for antibody production in vitro by plaque‐forming cells from trout, Salmo gairdneri (Richardson), and mice
Authors: van Glnkel F. W. , van Muiswinkel W. B. , Merchant B. , Lizzio E. F. , Dixon O. W. , Anderson D. P.
Published: January 2006

Anterior kidney and splenic cells were taken from rainbow trout and splenic cells from BALB/c mice immunized with a T‐dependent (sheep red blood cells) or T‐independent (DNP‐Ficoll) antigen. The cells were incubated at different temperatures in Jerne plaque assays (direct or passive haemolytic plaque assays). The optimum numbers of in vitro plaque‐forming cells (PFC) after incubation with homologous complement were directly correlated with normal body temperatures of the respective species. The optimum incubation temperature was 37°C for mouse cells and 10°C for fish cells. Incubation of mouse cells at lower temperatures of 30, 20, 10, 4 or 0°C appeared to yield a direct line reduction in numbers of PFC. Trout cells developed significantly fewer PFC at 4 and 20°C and none at 30°C or above; however, significant numbers still appeared at 0°C. More PFC per million white blood cells were obtained from the anterior kidney; however, related to temperatures, no differences in development of numbers of PFC could be seen between the spleen and anterior kidney cells of trout. When the incubation time was lengthened for both trout and mouse cells held at low temperatures, the numbers of PFC approached those of the cells incubated at the optimum temperatures for 10 h.
The influence of photoperiod on sexual development in underyearling rainbow trout, Salmo gairdneri Richardson
Authors: Skarphedinsson O. , Bye V. J. , Scott A. P.
Published: January 2006

Photoperiods of 19 h light or more induced sexual maturation in male underyearling rainbow trout but did not influence maturation in the females. Early maturation was not a consequence of the increased growth under long photoperiods. The rate of mortality was much higher in the early maturing males than in the immature fish.
Switches between zoophagy, phytophagy and detritivory of Sarotherodon mossambicus (Peters) populations in twelve man‐made Sri Lankan lakes
Authors: Maitipe P. , De Silva S. S.
Published: January 2006

The diet of 1200 adult Sarotherodon mossambicus [16–37 cm total length (t.l.)] in 12 man‐made Sri Lankan lakes, belonging to five different irrigational systems were studied over four climatic seasons using volumetric analysis. Food differed between seasons and reservoirs but overall, the diet consisted of 2, 2, 6 and 15 genera of diatoms, blue‐green algae, green algae and animal material respectively. However, none of the S. mossambicus populations maintained either a detritivorous, phytoplanktivorous or a zooplanktivorous habit through the year. Detritivory was most common during the rainy season while phytoplanktivory predominated in the dry season. Blue‐green algae were not an important constituent of the diet. Out of the 12 reservoir populations, five were predominantly detritivorous, six phytoplanktivorous and one zooplanktivorous. Detritus was completely absent in the ingested material in certain populations when they devoured animal or plant material, indicating the ability of S. mossambicus to switch from deposit to suspension feeding. The mean relative intestinal length (m.r.i.l.) of S. mossambicus ranged between 5–1 and 15–2. The m.r.i.l. decreased significantly with increasing body length: m.r.i.l. = 14–1 –0.018 T.L. (r=–0.89; P<0.001).
Double ovulatory cycles in some captive turbot, Scophthalmus maximus L.
Authors: McEvoy L.‐A.
Published: January 2006

The hypothesis that the paired ovaries of turbot, Scophthalmus maximus, ovulate alternately was tested and rejected as a possible explanation for the double ovulatory cycles found in some captive turbot. It is suggested that these double cycles are caused by variation patterns in the hormone‐release cycles of individual females.
Genetic differences between the Chinese and European races of the common carp, Cyprinus carpio L. IV. Effects of sexual maturation on growth patterns
Authors: Hulta G. , Wohlfarth G. , Moav† R.
Published: January 2006

A study of growth curves of common carp of the Chinese and European races was aimed at gaining more understanding of the genetic and developmental interrelations between growth and sexual maturation. A negative association between growth rate and onset of sexual maturity was noted particularly in the Chinese race. Gonad development in males of the Chinese race is faster, and starts earlier, than that of the European race. The Chinese x European crossbred shows incomplete dominance in the direction of the European parent for this trait. Heterosis for growth under harsh conditions (as of the Chinese parent) and slow sexual development (as of the European parent), acting together, result in over–all heterosis of the Chinese x European crossbred.
Aerobic metabolic scope and swimming performance in juvenile cod, Gadus morhua L.
Authors: Soofiani N. M. , Priede I. G.
Published: January 2006

Juvenile cod (Gadus morhua) were made to swim in a tunnel respirometer to determine the oxygen consumption during swimming at different speeds. Results were compared with measurements of standard and active metabolic rates in static respirometers before and after intense exercise. The oxygen consumption at maximum sustainable swimming speed was considerably lower than the peak oxygen consumption following exhausting exercise. It is suggested that these fish have a poorly developed system of aerobic (red) locomotor muscles which do not normally make a major demand upon oxygen consumption. Apparent specific dynamic action following feeding and repayment of oxygen debt following anaerobic exercise can each give rise to greater rates of oxygen consumption. Following exhausting exercise there is a delay of about 1 h before oxygen consumption reaches a peak level some 40% higher than the peak level observed during sustained swimming.
X‐ray microtags for identification of individuals in studies of fish energetics
Authors: Higgins P.J.
Published: January 2006

In a study following growth and food intake of individuals within a population it was important to obtain individual rather than group mean measurements. A technique is described which combined the benefits of X‐ray readable microtags with the radiographic method for measuring food intake described by Talbot & Higgins (1983). Its usefulness was established in an eight–month study on hatchery reared juvenile Atlantic salmon, Salmo salar L.
Effects of dietary polyunsaturated fatty acid deficiencies on mortality, growth and gill structure in the turbot, Scophthalmus maximus
Authors: Bell M. V. , Henderson R. J. , Pirie B. J. S. , Sargent J. R.
Published: January 2006

The preparation of fish oil concentrates containing only (n‐3) polyunsaturated fatty acids (PUFA) with different ratios of 20:5 (n‐3)/22:6 (n‐3) is described. Three groups of turbot were maintained on different diets containing: 1, 10% of the dry weight of the diet as natural fish oil, equivalent to 2.5% (n‐3) PUFA and 0–23% (n‐6) PUFA; 2, 10% of the dry weight of the diet as palmitic acid, i.e. no PUFA; 3, 8–7% palmitic acid and 1–3% of the dry weight as (n‐3 PUFA and negligible (n‐6) PUFA. Only the fish on the diet containing natural fish oil showed significant growth over a 15‐week period. In addition there were high mortalities on the two experimental diets (2 and 3). Changing the ratio of 20:5 (n‐3)/22:6 (n‐3) from 13–8 to 2–2 in the diet containing 1 3% (n‐3) PUFA and negligible (n‐6) PUFA markedly decreased the mortalities. Fish fed the two experimental diets (2 and 3) developed gross changes in gill structure involving the disappearance of chloride cells, a ‘sloughing off’ of the epithelium along the primary and secondary filaments and an accumulation of cellular material in the inter‐lamellar spaces. The tissue ultimately disintegrated to leave a skeleton of connective tissue and a mass of cellular material in the inter‐lamellar spaces. It is concluded that 22:6 (n‐3) is an essential fatty acid for turbot and that the gill epithelium is a sensitive indicator of this deficiency in this species.
Differences in the susceptibility of brown trout, Salmo trutta L., and American brook trout, Salvelinus fontinalis (Mitchill), to infestation by the peritrich ciliate, Scyphidia sp.
Authors: Pickering A. D. , Strong A. J. , Pollard J.
Published: January 2006

A hitherto undescribed species of Scyphidia has been shown to infest the skin of brown trout. However, it is incapable of colonizing the skin of American brook trout, even when these fish are co‐cultivated with heavily infested brown trout. Possible mechanisms accounting for this host/parasite specificity are discussed.
Preliminary investigation of the characteristics of fish lymphocytes separated on a Percoll discontinuous gradient
Authors: Blaxhall P. C. , Sheard P. R.
Published: January 2006

This investigation was carried out to determine if lymphocyte functional heterogeneity could be demonstrated in teleosts on the basis of density difference. The lymphocytes separated into two fractions on a Percoll discontinuous gradient. The less dense lymphocytes separated at 1.056gml−1 and contained both moderately villous and smooth lymphocytes, whereas the more dense lymphocytes separated at 1.07 g ml−1 and were predominantly moderately villous lymphocytes. The moderately villous lymphocytes had a higher mitochondria content than the smooth lymphocytes. Lymphocytes separating in the 1.056g ml−1 layer were more responsive to stimulation with polyclonal mitogen (PHA) than the lymphocytes separating in the 1.07 g ml−1 layer. This indicates that the lymphocytes separated according to either cell lineage or maturity.
Migration tendency in juvenile steelhead trout, Salmo gairdneri Richardson, injected with thyroxine and thiourea
Authors: Birks E. K. , Ewing R. D. , Hemmingsen A. R.
Published: January 2006

Juvenile steelhead trout, Salmo gairdneri injected with thyroxine (T4) near the time of seaward migration exhibited a significantly lower migration tendency than untreated controls of fish injected with saline, thiourea, or a combination of T4 and thiourea. Fish injected with thiourea alone or in combination with T4 prior to the time of maximum migration tendency showed enhanced migration over untreated and saline injected controls and those injected with T4 alone. Injections of T4 or a combination of T4 and thiourea elevated plasma T4 and tri‐iodothyronine (T3) concentrations, while injection of thiourea alone depressed thyroid hormone levels relative to saline‐injected controls. Plasma concentrations of T3 and T4 returned to control levels within 10 days in all groups. We suggest that thyroid hormones are antagonistic to mechanisms underlying seaward migration of steelhead trout and that these antagonistic effects must be overcome before migration tendency is expressed.
Factors affecting growth and recruitment of yellow perch, Perca flavescens Mitchill, in South Bay, Lake Huron
Authors: Henderson B. A.
Published: January 2006

Five hypotheses explaining variations in growth and recruitment were tested statistically with data from a study of yellow perch, Perca flavescens, 1950–83. Recruitment was not a function of water temperature during spawning, hatching or the first year, but was a function of lake water levels. Growth was not related to average water temperatures or degree‐days, but was inversely correlated with the abundance of year‐classes.
Age determination and growth of yellow eels, Anguilla anguilla (L.), from a brackish water, Norway
Authors: Vøllestad L. A.
Published: January 2006

This paper describes the age determination of European yellow eels from a brackish water area in south‐east Norway. Two different methods were used; clearing in 96% ethanol or burning and cracking. When reading the otoliths twice using the same method, the same age was found in 40% of the readings, a discrepancy of 1 year was found in another 40% of the readings (both methods). Burning and cracking yielded age estimates which were on average 1.25 years higher than those obtained by clearing.
Cytogenetic techniques in fish genetics
Authors: Hartley S. E. , Horne M. T.
Published: January 2006

A modification of a previously described method of fish blood lymphocyte culture is described and discussed with the results of various chromosome banding protocols as applied to fish chromosomes.
On the accuracy of age‐determination using scales from rudd, Scardinius erythrophthalmus (L.), of known age
Authors: Mann R. H. K. , Steinmetz B.
Published: January 2006

Six scientists from five European countries each examined 29 sets of scales from rudd of known age. The material contained 174 scales from both fast and slow growing fish and, with the exception of one participant, the scientists missed the first annulus when it was formed close to the scale centre. Sixty‐eight scales were misread in this way, but only 12 were incorrectly aged because of confusion between true and false annuli. Comparisons of back‐calculated lengths with observed lengths at each age were used to identify which false annuli had been incorrectly identified as true annuli, and vice‐versa. The results confirmed the necessity of having information from other sources, e.g. seasonal length‐frequency distributions of 0‐group fish, to support the subjective interpretation of the scales.
A histological study of the hypophysial‐gonadal system during sexual maturation and spawning in the milkfish, Chanos chanos (Forskal)
Authors: Tan J. D.
Published: January 2006

The pituitary gland of the milkfish, Chanos chanos, was studied at different stages of sexual maturation and spawning. Consecutive median sagittal sections were treated with a range of stains to demonstrate the different cell types and regions. The milkfish pituitary consists of a neural component, the neurohypophysis, and an epithelial component, the adenohypophysis, which in turn consists of three regions: the rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). However, unlike most teleosts, the pituitary gland of the milkfish is encased in a bony chamber, has dorsal and ventral lobes and extends anteriorly from its point of origin at the base of the brain. PAS (+) basophils are found in all regions of the adenohypophysis, but mostly in the proximal pars distalis. These cells undergo hypertrophy and hyperplasia during sexual maturation, shrinkage and degranulation during spawning.
Fish–macrophyte relationship in the Anavilhanas Archipelago, a black water system in the Central Amazon
Authors: Araujo‐Lima C. A. R. M. , Portugal L. P. S. , Ferreira E. G.
Published: January 2006

The characin fish fauna associated with floating meadows on the floodplain of the Rio Negro was studied at the beginning of the rising water period. Two microhabitats were identified in the meadows (Paspalum plus Oryza vegetation and pure Oryza vegetation) and their influence on characin abundance tested. No significant difference in characin numbers was found between microhabitats. Three species accounted for 82% of characins captured: Hemigrammus levis, Metynnis cf. hypsauchen and Moenkhausia lepidura. Metynnis cf. hypsauchen was more abundant in Paspalum plus Oryza vegetation than in the other microhabitat. A similar difference was not found for H. levis and M. lepidura. The diets of the three species were similar in the smaller size classes, consisting primarily of Cladocera. However, the diets differed in the larger size classes with M. cf. hypsauchen foraging mainly on filamentous algae, M. lepidura on wild rice and H. levis on Cladocera. The diet shift is apparently an optimal foraging strategy, while the differences in microdistribution appear to be related to predation risk.
Age, growth and reproductive strategy of the snakehead, Ophicephalus striatus Bloch, from Sri Lanka
Authors: Kilambi R. V.
Published: January 2006

A total of 281 snakehead‐lula, Ophicephalus striatus, collected between November 1982 and June 1983 from inundated rice fields and swamps in south‐western Sri Lanka were analysed. Age determination by length frequencies and scale annuli revealed six age groups. An asymptotic length of 520 mm was estimated by the von Bertalanffy growth model.

The ova were assigned to four developmental stages and a maturity scale was developed for the females. Fast growing 2‐year‐old fish attain sexual maturity. The ovum size frequencies and occurrence of mature and spent fish indicate that this fish spawns during the south‐west monsoon season. Fecundity estimates ranged from 1688 to 7146 ova. Total length and weight are equally useful for predicting fecundity.
Juvenile roach and invertebrate predators: delaying the recovery phase of eutrophic lakes by suppression of efficient filter‐feeders
Authors: Brabrand Å. , Faafeng B. , Nilssen J. P. M.
Published: January 2006

Two large pelagic enclosures were installed in a culturally eutrophic lake to assess the importance of predation by immature fish and invertebrate predators on efficient filter‐feeders. Predation pressure in the pelagic zone from invertebrate predators (mainly Cyclops scutifer) was similar to that from 2‐year‐old roach and led to suppression of the most important filter‐feeding genus Daphnia. Those predators thus may have a stabilizing effect on culturally eutrophic lakes, by maintaining the eutrophic phase beyond the predictions from spring nutrient values. To speed up the recovery of such lakes it is necessary to suppress both types of predators.
The role of female competition in the mating success of two clones of the Amazon molly, Poecilia formosa
Authors: Woodhead A. D. , Carlson C.
Published: January 2006

Clones of the unisexual fish Poecilia formosa, the Amazon molly, live in the wild in association with their progenitor bisexual species, and compete with them for resources. These resources include food, space and also mates, since the Amazon molly reproduces gynogenetically, a process in which sperm transferred from a male host species activates their eggs. Earlier studies of the adaptive mechanisms that facilitate the coexistence of the bisexual and unisexual forms have focused upon male behaviour, but recent work with another unisexual species, Poeciliopsis, demonstrated that female aggressive behaviour may play an important part in determining the ecological standing of a clone.

We have extended our observations to female mating behaviour in two clones in the Amazon molly; clone 1 that does not thrive well under laboratory culture; and clone 2 that is hardy and survives very well. There was no aggression between the clones, nor did the clones show aggression towards females of the bisexual species. However, clone 1 consistently was more successful in the number of mating encounters made with the male; it approached the male more often than clone 2 and fled from the male less often. Males also showed some preference for mating with clone 1 females. If there are physiological differences in the wild clones similar to those seen in the laboratory, the mating advantage of the less robust clone 1 may ensure its continued survival in competition with a more vigorous clone.
Biochemical indicators of thermal stress in Tilapia aurea (Steindachner)
Authors: Kindle K. R. , Whitmore D. H.
Published: January 2006

Tilapia aurea muscle and liver adenylate nucleotides, the adenylate energy charge (EC), plasma glucose, cortisol and chloride were monitored during acute and chronic temperature stress. Muscle EC is unaffected during acute cold water exposure but decreases significantly when tilapia are exposed to chronic, sublethal, low temperature stress. The decrease in EC is primarily the result of a decrease in ATP concentration. Plasma glucose and cortisol increase when tilapia are exposed to 11–12° C for 60 min, 11 days, and a 5‐week period. Incomplete compensation is evident in 5‐week acclimated fish since glucose and cortisol levels are intermediate between controls and acutely stressed fish. Acclimation to 35° C does not significantly affect plasma glucose and cortisol compared to controls (22° C). Plasma chloride is relatively unaffected by acute and chronic temperature stress. Liver adenylates are not significantly affected when tilapia are subjected to a sudden drop in water temperature (22° down to 11° C). EC is a useful indicator of chronic low temperature stress in T. aurea, while plasma glucose and cortisol are sensitive to both acute and chronic temperature stress.
Post‐embryonic development of water‐ and airbreathing organs of Anabas testudineus (Bloch)
Authors: Hughes G. M. , Munshi J. S. DATTA , Ojha J.
Published: January 2006

The development of respiratory surfaces in post‐embryonic stages of Anabas testudineus was studied using morphometric methods on serial sections through the pharyngeal region of specimens obtained by induced breeding of known parentage. The larvae and fry were fixed in glutaraldehyde and osmium tetroxide. In the young stages aquatic respiration was found to be obligatory. The hatchlings come out of the egg membranes about 10 h after fertilization. During the yolk‐sac stages gaseous exchange takes place through the well vascularized skin. The gills start differentiating at about 24 h and become functional at about 39 h. The labyrinthine organs begin to develop after 51 h but the hatchlings do not take an air breath until they reach 13–14 days. The appearance of scales at 11–14 days probably hinders cutaneous respiration and is correlated with the onset of aerial respiration.

Morphometric analysis using stereological methods shows high surface: volume ratios for the gills and labyrinthine organs as adaptations to gas exchange function. A marked decrease in surface: volume ratio for the suprabranchial cavities between 7 and 11 days indicates an increase in volume to accommodate the expanding labyrinthine plates which retain a fairly constant surface: volume ratio.
Shock‐induced triploidy and its effect on growth and gonad development of the European catfish, Silurus glanis L.
Authors: Krasznai Z. , Márían T.
Published: January 2006

Triloidy was induced in European catfish, Silurus glanis L., by cold‐shocking eggs at 4°C for 30 and 40 min respectively, starting 5 min after fertilization. The hatching success of cold‐shocked eggs was 25–30%. Cold shocks longer than 1 h caused total mortality. The triploid character of the cold‐shocked European catfish was proved by karyological and red blood cell size analyses. The gonads of the triploid fish were significantly smaller than those of the diploids, while the growth rate values of the triploids were significantly higher than those of the diploids.
Bacteria—food or food competitors of silver carp, Hypophthalmichthys molitrix Val.?
Authors: Bitterlich G. , Schaber E.
Published: January 2006

The role of bacteria in the nutrition of silver carp was studied by in‐vitro tests, which confirmed earlier results that the potentially important source of nitrogen in bacteria is not utilized by the fish. Cultures of aerobic and anaerobic bacteria, recovered from a fish pond, were incubated with digestive fluids from the gut contents and from tissues surrounding the alimentary tract (Organ of Leydig) respectively. Growth of aerobic isolates was not affected by the digestive fluids whereas growth of all anaerobes was inhibited. A susceptibility test revealed a bacteriostatic rather than bactericidal effect of the digestive fluid on the bacteria. During 42 h incubation at approximately 20°C of gut fluid, trypsin activity decreased between 14% (in fore‐gut fluid) and 62% (in mid‐gut fluid). The addition of aerobic bacteria (to the mid‐gut fluid) or anaerobic bacteria (to the fore‐gut fluid) did not accelerate the degradation of trypsin.
The dissolved oxygen and temperature requirements of Atlantic salmon, Salmo salar L., in the Thames Estuary
Authors: Alabaster J. S. , Gough P. J.
Published: January 2006

An improvement in water quality in the estuary of the River Thames in recent years, coupled with the return of adult Atlantic salmon following artificial stocking of the headwaters with parr and of the lower river with smolts, has provided an opportunity to define the dissolved oxygen requirements of adult fish ascending the estuary to reach fresh water. Between July and September 1984 the fish traversed a length of 30 km where the concentration of dissolved oxygen was at its lowest, the 5‐percentile and median values being 1.6–2.6 and 3.5–5.9 mg l−1, respectively, depending upon exact location. Within this zone there was a length of about 20 km in which the minimum at any one time during the period was always less than 5mg l−1 and a shorter length of 15 km in which it was always less than 4.7 mg l−1, and it is likely that some fish experienced even lower values during their upstream passage. Over lengths of 1, 10 and 30 km, for example, the 10‐percentiles were 2, 2.2 and 2.8 mg l−1, respectively, the medians were 3.6, 3.8 and 4.3 mg l−1, respectively and the 90‐percentiles were 4.8, 4.9 and 5.3 mg l−, respectively. The water temperature during August, when most of the fish were caught, was never lower than 19°C and there was a length of estuary of at least 20 km where it exceeded 22°C.
Light‐ and electron‐microscope studies on the pseudobranch of the golden orfe, Leuciscus idus L.
Authors: Fischer‐scherl Th. , Hoffmann R.
Published: January 2006

The structure of the pseudobranch of the golden orfe is described from light‐ and electron‐microscopical observations. It is characterized as a covered pseudobranch overlaid by a mucous membrane. The pseudobranch of the golden orfe has no respiratory function, but the electronmicroscopical results indicate that it could function endocrinally by registering and regulating salinity or osmolarity. The epithelial cells are represented by pseudobranch‐type cells. No chloride cells were seen. Rodlet cells are located near blood vessels at the base of the pseudobranch and in the covering epithelial layer, together with mucous cells and mast cells. In the endothelial intima of the arteries the so‐called Weibel‐Palade bodies are described.
Observations on granulocyte peroxidase in New Zealand freshwater eels, Anguilla species
Authors: Hine P. M. , Wain J. M. , Dunlop D. M.
Published: January 2006

Peroxidase activity in the granulocytes of eels was investigated using o‐tolidine, paraphenylene‐diamine‐pyrocatechol, and 4‐chloro‐l‐naphthol as substrates, and cyanide, azide and aminotriazole as inhibitors. Most circulating neutrophils of Anguilla australis Richardson, 1848 and A. dieffenbachii Gray. 1842 showed no peroxidase activity at pH 7.6 and pH 9.0, but a few neutrophils, thought to be mature, were positive. Another granulocyte in the anterior kidney, spleen, parasitized gill tissue and, rarely, the blood contained a cyanide‐resistant, azide‐inhibited, peroxidase and was tentatively identified as the eosinophil. Neutrophils of A. anguilla (L.) showed granular peroxidase activity which was inhibited by cyanide. The eosinophil was not observed.

Absence of peroxidase from most circulating neutrophils in A. anguilla and A. dieffenbachii, and its pattern in the neutrophil precursors and mature neutrophils of A. anguilla, may be due to two morphologically indistinguishable granule types. Primary peroxidase‐negative granules occur in precursors and immature neutrophils and secondary peroxidase‐positive granules in mature neutrophils of all three eels. Circulating neutrophils in New Zealand eels seldom mature and are theretore peroxidase‐negative, whereas A. anguilla neutrophils are mature and are usually peroxidase‐positive.

Impairment of microbicidal activity in neutrophils lacking peroxidase is discussed.
Light and electron microscopic studies on the enzyme cytochemistry of leucocytes of eels, Anguilla species
Authors: Hine P. M. , Wain J. M. , Boustead N. C. , Dunlop D. M.
Published: January 2006

The leucocytes of three anguillid eels were studied using enzyme cytochemistry. Leucocytes were stained for peroxidase, alkaline phosphatase, acid phosphatase, aryl sulphatase, β‐glucuronidase, N‐acetyl‐β‐glucosaminidase, β‐galactosidase, lysozyme, a variety of non‐specific esterases, chloroacetate esterase and two proteases. All cells were negative for aryl sulphatase, β‐glucuronidase, N‐acetyl‐β‐glucosaminidase, and β‐galactosidase. Very few neutrophils, thought to be mature, and all eosinophils contained peroxidase‐positive granules, and some monocytes showed very weak peroxidase staining. All leucocytes lacked alkaline phosphatase, but all cells except lymphocytes and thrombocytes of A. dieffenbachii contained acid phosphatase. Neutrophil acid phosphatase released into phagosomes was associated with Escherischia coli bacteriolysis. Neutrophils also secrete lysozyme and, with monocytes, produce and secrete a variety of esterases. The possible interaction of lysozyme, acid phosphatase and esterases in bacteriolysis is discussed.
Danger at dawn: experimental support for the twilight hypothesis in shoaling minnows
Authors: Pitcher T. J. , Turner J. R.
Published: January 2006

This experiment aimed to compare responses to predator threat at dawn and in daylight. Using silicon‐intensified video, shoaling European minnows, Phoxinus phoxinus (L.), were observed in large tanks furnished to simulate natural conditions and equipped with artificial dawn and dusk illumination. In the dark, fish were observed under infra‐red light. The appropriate light level for dawn predator exposure was determined behaviourally. During dawn, the behaviour of individual focal minnows was systematically recorded at five light levels set by the behaviour of fish in pilot work.

On six predetermined dawn and daytime occasions over a period of 3 weeks, minnows feeding on an artificial vertical feeding patch were subjected to a standardized stalk by a model pike. Under daytime illumination (8 μEm−2 s−1), the minnows were presented with patches once per day. The feeding patches were presented early in the artificial dawn (0.5–1.5 μm−2 s−1) only on days when fish were to be subjected to the model pike.

Fish became active at the onset of dawn. A behaviour which appeared at this time is reported for the first time: minnows rose to the surface, appeared to take in and expel bubbles of air, and descended. Shoaling responses and swimming speeds increased soon after the start of dawn. Foraging increased slightly later than this, when illumination had reached about one‐fifth of the daytime level. This was the level chosen for predator exposure.

When approached by the pike model at dawn, minnows abandoned feeding on the patch only when the pike reached one‐third of the distance which it obtained under daylight. Individual fish detecting the approaching threat showed skitter and inspection behaviour similar to that observed in daylight, but these behaviours peaked much later in the pike's stalk than in daylight. We conclude that minnows at dawn fail to detect the approaching pike until it is much closer than in daylight; we believe that the work therefore provides the first experimental support for the ‘twilight hypothesis’ that, under low light levels, stalking predators have an advantage over shoaling prey.
The influence of species composition on behaviour in mixed‐species cyprinid shoals
Authors: Allan J. R.
Published: January 2006

Adult dace, minnows and gudgeon (50 of each) were studied in a fluvarium. Each possible paired‐and three‐species combination was compared with single‐species controls. Species position in the fluvarium and the behaviour of marked individuals were used to measure interactions. Individual behaviours were standardized for day‐to‐day changes in activity level. The presence of a second species caused significant increases in the frequency and total time of behaviours associated with positional change. Such behavioural changes may reduce competition by adjusting individual position within the shoal. Minnows moved higher in the water and downstream in the presence of dace. Gudgeon moved lower in the water and downstream in the presence of dace and of minnows. Dace made slight, but significant, movements downstream and higher in the water column in response to both minnows and gudgeon. These shifts were very distinct, and the resulting shoal structure mirrors the positions occupied in mixed‐species shoals of these species in the wild.
Are ‘preferences’ and ‘tolerances’ in cichlid mate choice important for speciation?
Authors: Crapon de Caprona M.‐D.
Published: January 2006

Although early experience influences the development of preferences in cichlid mate choice, the same species can be very ‘tolerant’ and spawn with members of other species appearing very different from conspecifics. The conditions under which such interspecific spawnings occur in captivity are described, and are considered to exist in the field.

Many cichlid species are genetically similar, and interspecific spawning often produces fertile hybrids. Pre‐mating behavioural barriers to hybridization are important. The ability of cichlids to develop preferences based on subtle cues, but also to produce fertile hybrids, is discussed in the context of speciation: genetic isolation of morphs (and possibly of hybrids) from their parental species, through social learning.
Tilting behaviour of the Atlantic mackerel, Scomber scombrus, at low swimming speeds
Authors: He P. , Wardle C. S.
Published: January 2006

Negatively‐buoyant Atlantic mackerel, Scomber scombrus L., (fork length 30–39 cm) tilt their bodies with the head up while swimming at speeds below 0.8 body length per second (B.L. s−1). This behaviour is quantitatively described by the body attack angle and swimming speed measured from film records. The maximum recorded body attack angle was 27° in a 32 cm‐long fish swimming at 0.45 B.L. s−1 while its nose followed a course close to the horizontal. In general, larger body attack angles were shown at lower swimming speeds and were associated with denser bodies at each speed. We consider that this behaviour pattern allows the fish to maintain a chosen swimming depth while its body creates lift by acting as a hydrofoil. Lift from the fins is insufficient at low swimming speeds.
Growth energy partitioning by juvenile bluegill sunfish, Lepomis macrochirus Rafinesque
Authors: Booth D. J. , Keast J. A.
Published: January 2006

Growth energy build‐up and partitioning by immature bluegill sunfish were studied over the summer months from May to September 1984. Fish sampled in May showed low condition and low lipid reserves. Condition was restored to summer levels within the following month. Fat reserves were built up from 7% to 14% of body weight over the entire summer. Most (80%) of the annual length increase occurred from 1 June to 15 August. Over the winter period (October‐April) condition dropped and lipids were depleted. Calculations showed that energy liberated through lipid depletion over this period could supply the energy requirements of inactive wintering fish. It is concluded that the sequencing of growth energy diversion into changes in body length, condition, and lipid build‐up enhances mid‐summer growth and overwinter survival.
Induction of enhanced alkaline phosphatase activity in the melano‐macrophage centres of Oreochromis aureus (Steindachner) through starvation and vaccination
Authors: Agius C. , Couchman W.
Published: January 2006

Employing histochemical methods, alkaline phosphatase activity was studied in the melano‐macrophage centres of the spleen of the cichlid fish Oreochromis aureus (Steindachner). Enzyme activity was observed to be very low in normal fish. Prolonged starvation induced an enhanced enzyme response. Starvation followed by antigenic stimulation through an intraperitoneal injection of a bacterial vaccine further elevated the levels of alkaline phosphatase activity. The marked response of the pigment‐bearing macrophages to bacterial antigen provides further evidence of the lymphoreticular nature of these pigmented cell aggregates. The association of alkaline phosphatase activity and lipofuscin (the most common pigment in fish melano‐macrophage centres) with phagocytic cells has been documented in higher animals including
The influence of temperature on the embryonic development of three cyprinid fishes, Abramis brama, Chalcalburnus chalcoides mento and Vimba vimba
Authors: Herzig A. , Winkler H.
Published: January 2006

The influence of temperature on the embryonic development of three European cyprinid fishes, Abramis brama, Chalcalburnus chalcoides mento and Vimba vimba, was studied with respect to hatching efficiency and the functional relationship with the duration of development. The functional dependance of the duration of development on temperature is well described by a power function with a correcting constant for temperature. Comparison with published data for other cyprinids shows that the response of embryos to temperature, together with the various temperature controlled responses of adult fishes, is a valuable aid for the ecological characterization of the different species.
The growth of herring larvae, Clupea harengus L., in the Clyde: an assessment of the suitability of otolith ageing methods
Authors: Geffen A. J.
Published: January 2006

Wild herring larvae were sampled from the Firth of Clyde, Scotland in 1980 and 1981 to assess the suitability of otolith ageing methods for herring larval studies. The ages and growth rates were estimated directly from otolith ring counts, by comparison of ring counts with the results of validation studies on reared larvae of known age, and by back‐calculation. Growth rates based on otolith data were compared with indirect calculations based on length at capture. The assumption of daily ring deposition, even allowing for a period of lag before the initiation of daily ring deposition, led to incorrect predictions for age at yolk‐sac absorption, and back‐calculations led to overestimated growth rates, indicating that ring deposition does not begin at hatching and that light microscope counts give a rate different from one ring per day in wild herring larvae.
A key to the species of Acanthocephala parasitic in British freshwater fishes
Authors: Brown A. F. , Chubb J. C. , Veltkamp C. J.
Published: January 2006

We present methods for the collection, fixation, preservation and examination of the acanthocephalans parasitic in British freshwater fishes. An illustrated key to the species is provided.
The effects of intra‐ and inter‐specific competition on the survival and growth of stocked juvenile Atlantic salmon, Salmo solar L., and resident trout, Salmo trutta L., in an upland stream
Authors: Kennedy G. J. A. , Strange C. D.
Published: January 2006

The relative effects of inter‐ and intra‐specific competition on the survival and growth of stocked salmon were investigated in an upland trout stream during summer and winter 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. Salmon fry stocked into the cleared area survived more than twice as well and grew significantly larger than those stocked into the area containing trout and older salmon. Intra‐specific competition from older salmon in the second year of stocking in the cleared area significantly reduced the survival and growth of the O+ salmon. However, these were still significantly larger and survived better than those in the control area where inter‐specific competition from trout was maintained. Some immigration of trout to the cleared area occurred; these showed greatly enhanced growth rates compared to those in the control area, reflecting low intra‐specific trout competition in the former. Inter‐specific competition effects of older salmon on both trout fry growth and survival were also detected, although the latter did not become apparent until the winter. This is discussed in terms of the relative importance of biotic and abiotic regulating mechanisms. Evidence of allopatric niche segregation is also discussed, since salmon in the cleared area did not have a biomass equivalent to that in the area which also contained trout.
Seasonal changes in serum lipid composition of the plaice, Pleuronectes platessa L.
Authors: White A. , Fletcher T. C. , Pope J. A.
Published: January 2006

Seasonal changes in the major lipid classes of plaice serum were examined in fish caught off the north‐east coast of Scotland. Both male and female plaice were sampled monthly between June 1983 and May 1984. Total lipid, total cholesterol, free cholesterol, triglycerides, phospholipids and non‐esterified fatty acids were measured using commercial kits validated against standard reference methods. There were no significant differences in lipid levels between male and female fish and, although there were real differences between months for each lipid class, there was no regular pattern over the 12‐month period. All the lipid class values, however, reached a maximum in September, which could be related to the increase in feeding after spawning. The smaller peak in February could be associated with the mobilization of lipid reserves for gonadal development and to overcome the effect of starvation during spawning.
Changes in the species composition of anglers' catches in the River Trent (England) between 1969 and 1984
Authors: Cowx I. G. , Broughton N. M.
Published: January 2006

Data on anglers' catches on the River Trent were collected for the seasons 1969/70 to 1983/84 using postal questionnaires. During this period 60.4t of fish were caught during a total fishing effort of 526 871 man‐h or 60.15 man‐years, and more than 20 species of fish were recorded. The percentage of anglers making a catch (70–80%) and the catch per unit effort, mean 114.7g man‐h −1, were comparable with those reported for other waters.

Roach and gudgeon were the most commonly captured species with chub, bleak, bream, eels and dace also forming major components of anglers' catches. Since 1969 chub, bream, eels and perch have made an increasingly greater contribution to catches, coupled with a decline in numbers of roach and dace. It is suggested that improvement in water quality and its implication on interspecific competition was the most likely cause of the changes.
Gillnet selectivity and the efficiency of alternative combinations of mesh sizes for some freshwater fish
Authors: Jensen J. W.
Published: January 2006

The selectivity curves of nylon gillnets for burbot and two groups of Arctic charr of different fatness were found by the Gulland‐Harding method. They are compared to the selectivity curves of whitefish, brown trout, and perch. Based upon these curves and the relationships between most efficient mesh size and fish length, the pooled relative efficiency of a geometrical and an arithmetical series of mesh sizes was calculated for salmonids, burbot, and perch. This efficiency of the geometrical series is different for the three groups of fish, but equal for each group over the interval between the modal lengths of the smallest and largest mesh sizes. The efficiency of the arithmetical series is also different for the three groups, increases linearly with fish length, and is valid over the interval between the modal lengths of the second smallest and the second largest mesh sizes. Each series has its special advantages, and both are easily adjusted to the fish length interval of interest. They are especially adapted for the catch of salmonids. For these, the variations of condition factor is more important than any characteristics of the species, and its influence upon the most efficient mesh size to fish length relationship and the pooled relative efficiency of the two series of nets is evaluated.
Studies on lesions caused by plerocercoids of Triaenophorus nodulosmin some fish of an alpine lake, the Königssee
Authors: Hoffmann R. W. , Meder J. , Klein M. , Osterkornj K. , Negele R. D.
Published: January 2006

Lesions caused by plerocercoids of Triaenophorus nodulosus in the second intermediate hosts were studied in fish of an alpine lake, the Königssee. Four species (Arctic charr, Salvelinus alpinus; minnow, Phoxinus phoxinus; burbot, Lota lota: perch, Percafluviatilis) could be shown to be affected, whereas seven other fish species did not have macroscopical or histological signs of invasion. The capsules of T. nodulosus plerocercoids were usually located in liver tissue. Whereas only living parasites were found in charr and minnow, dead and destroyed plerocercoids could be demonstrated additionally in burbot and perch.

The histological picture is characterized by capsules surrounded by connective tissue and by fresh or older migration routes in charr and minnow. Furthermore, larvae migrating through the biliary ductules were found regularly in charr. In burbot and perch, different stages of destruction of the parasitic larvae took place. The ability to reject the parasite by immunological reactions seems to depend on the species of host. Even if heavy changes in the liver tissue could be demonstrated, no negative influences on condition and growth of affected fish could be established.