bluuebunny/crossref_metadata_2025 huggingface dataset:
Sperm motility and fertilization time span in Atlantic salmon and brown trout—the effect of water temperature
Authors: Vladiĉ T. , Jätrvi T.
Published: April 2005

The effect of water temperature on the duration of sperm motility, the time lapse after activation by fresh water and the fertility of eggs was studied in Atlantic salmon and brown trout. Eggs of both species were fully fertile in fresh water after 512 s. No interspecific differences were noted in egg fertility at the lower water temperatures, but the brown trout eggs showed a higher resistance to high temperatures, indicating a better physiological thermotolerance. A highly significant effect of temperature on the overall duration of sperm motility was found, with a marked peak at 3−4°C for salmon and a weaker one for trout. After freshwater activation the eggs of both species remained fertile for a longer time than the sperm were mobile.
Recognition of sex‐inverting protandric Sparus aurata: ultrastructural aspects
Authors: Brusléa‐Sicard S. , Fourcault B.
Published: April 2005

Ovotestes of Sparus aurata were studied by histocytological means mainly during the post‐spawning period and at the beginning of the resting period, with the aim of determining the sex involved during the ensuing maturation. A testis displaying accomplished spermatogonial recovery was noted as an indicator of the absence of sex inversion. The recognition of oogenic activity which did not proceed beyond the perinucleolar stage revealed a developing ovary, but was not a sufficient criterion for determining the onset of sex inversion. The lack of spermatogonial renewal, early signs of testicular disorganization (shortness of seminiferous lobules, with few spermatogonia) and oogenic activity appeared to be indicators of an approaching sex inversion.
Diel migration and site fidelity in a stream‐dwelling cyprinid, Leuciscus leuciscus
Authors: Clough S. , Ladle M.
Published: April 2005

During May and June 1995, radio‐telemetry was used to record diel movements between different, clearly defined daytime and night‐time habitats in dace Leuciscus leuciscus. The frequent and often rapid return of individuals to previously occupied locations at dawn and dusk suggests differential habitat suitability according to light intensity, and appears similar in some respects to roosting behaviour in birds.
A multiductal system conveys digestive enzymes from the pancreas into the intestine in the Atlantic salmon
Authors: Einarsson S. , Davies P. S.
Published: April 2005

Light microscopic and scanning electron microscopic studies present strong evidence for a multiductal system conveying digestive enzymes from the exocrine pancreas into the anterior intestine in Atlantic salmon.
Morphological differences between wild and hatchery‐reared turbot
Authors: Ellis T. , Howell B. R. , Hayes J.
Published: April 2005

Reared 0‐group turbot originating from Irish Sea stock were heavier at a given length than wild fish due to a greater body width and body depth. A very high incidence (96%) of abnormal lateral line canals was noted in the reared fish. It is suggested that these morphometric and morphological differences developed during the larval stage.
Morphometric and genetic characterization of sympatric populations of Clarias gariepinus and C. anguillaris from Senegal
Authors: Agnèse J. F. , Teugels G. G. , Galbusera P. , Guyomard R. , Volckaert F.
Published: April 2005

A sample of African Clarias catfishes from the Senegal River was studied using morphometry, allozyme variation, microsatellites and RFLPs of mitochondrial DNA. They all confirmed the presence of two species, C. gariepinus and C. anguillaris. The two species were closely related genetically and no diagnostic loci were found in allozymes and microsatellites studies. Two of the 11 haplotypes of mtDNA observed were shared by both species. Three of the four assays (morphometry, allozymes and microsatellites) allowed a precise characterization of both. One specimen occupied an intermediate position in the analysis of the data; it was considered an Fl hybrid whose possible origin is discussed.
The influence of changes in food availability on the activities of key degradative and metabolic enzymes in the liver and epaxial muscle of the golden perch
Authors: Collins A. L. , Anderson T. A.
Published: April 2005

This study investigated the influence of feeding frequency on the activities of important degradative enzymes and potentially rate‐limiting enzymes in glycolysis and gluconeogenesis in the liver and white epaxial muscle of Macquaria ambigua. Adult animals were either fed daily to satiety (fed), deprived of food for up to 180 days (starved), or starved for 150 days then fed daily to satiety for 30 days (starved/fed). The activities of lipolytic, glycogenolytic and glycolytic enzymes in the livers of starved fish were maintained as long as liver energy stores were available, but became significantly reduced following their exhaustion indicating a decline in metabolism in response to prolonged starvation. The response of epaxial muscle metabolism to changes in food availability was different to that of the liver, as no significant change in the activities of muscle lipolytic or glycogenolytic enzymes were observed in response to starvation. Muscle tissue metabolism was reduced after 60–90 days of starvation, but then returned to prestarvation levels.
Effects of simulated trawling on sablefish and walleye pollock: the role of light intensity, net velocity and towing duration
Authors: Olla B. L. , Davis M. W. , Schreck C. B.
Published: April 2005

Laboratory apparatus which simulated capture of fish in the cod‐end of a towed trawl was used to induce post‐capture stress as measured by alterations in behavioural, physiological and mortality indices in juvenile walleye pollock Theragra chalcogramma and juvenile and adult sablefish Anoplopoma fimbria. Differences in resistance to net entrainment varied between species with the severity of stress and the potential for recovery depending on light intensity, net velocity and towing duration. At a light intensity which simulated daylight at depth in clear ocean water (0.5 μmol photons m−2 s−1), walleye pollock juveniles were able to maintain swimming in nets towed at 0.65 m s−1 for 3h with no discernible effects on behaviour or mortality. However, when net velocity was increased to >0.75m s−1 or light intensity was decreased to <0.002 μmol photons m−2 s−1, fish became entrained in the meshes of the net and exhibited significant alterations in feeding behaviour, predator evasion and increases in plasma cortisol concentrations. Marked increases in stress‐induced mortality also occurred, in some cases after a delay of 6 days and eventually reaching 100%. In comparison with walleye pollock, sablefish juveniles became entrained in the meshes of the net at higher velocities (>0.92m s−1) or lower light intensities (<0.0004 μmol photons m−2 s−1) and were much more resistant to post‐capture stress. Towing of net‐entrained fish for 15 min caused no detectable changes in feeding and cortisol and for 2 h, no changes in feeding although mortality increased from 0% for 15‐min tows to 19% for 2‐h tows. Towing for 4 h caused significant alterations in feeding and cortisol with feeding recovering to control levels by 6 days and cortisol by 3 days; mortality was 25%. When adult sablefish were towed for 4 h followed by 15‐min exposure to air, feeding was inhibited 6 days after towing, but recovered within 30 days with no mortality observed after 30 days. The results demonstrate the value of using laboratory‐based behavioural and biochemical indices to identify factors that may potentially affect post‐capture survival among different species of fish.
Accumulation of PSP toxins in Atlantic mackerel: seasonal and ontogenetic variations
Authors: Castonguay M. , Levasseur M. , Beaulieu J.‐L. , Grégoire F. , Michaud S. , Bonneau E. , Bates S. S.
Published: April 2005

Atlantic mackerel Scomber scombrus are known to be lethal vectors of paralytic shellfish poisoning (PSP) toxins to predators. To elucidate dynamics of PSP toxin accumulation in this species, mackerel were sampled in the Gulf of St Lawrence from May to October 1993. Mackerel appear to retain toxins (saxitoxin, gonyautoxins 2 and 3) year‐round. The toxin content of the liver, as determined by high performance liquid chromatography, increased significantly with fish age (r2=0.40) and length (r2=0.52), suggesting that mackerel progressively accumulate PSP toxins throughout their life. The toxin content of the liver also increased significantly during the summer feeding sojourn in the Gulf of St Lawrence. Comparison of profiles of saxitoxin derivatives indicated that zooplankton were the likely source of PSP toxins found in mackerel. The mean ± S.D toxin content was 17.4 ± 10.6 nmol liver−1 and the mean ± S.D. PSP toxicity was 112.4 ± 67.0 μg saxitoxin equivalents 100 g−1 liver wet weight (n=247).
Effects of variable discharge on the velocity use and shoaling behaviour of Phoxinus phoxinus
Authors: Garner P.
Published: April 2005

The swimming and shoaling behaviour of Phoxinus phoxinus was investigated in four identical channels connected to the River Frome, U.K. Minnows (mean length 29.5 mm) were stocked at an initial density of 100 fish per channel (22.2 fish m−2). The position of all visible fish in the channels was recorded at basal and elevated discharges, and use of velocity habitats inferred. Although a range of velocities (including zero) was present at both discharges, the fish selected higher mean velocities at elevated discharges than at basal discharges. Habitat suitability was significantly different between periods, emphasizing the effect of habitat availability and past experience upon habitat use. This appeared to result from the fish holding position at points with variable flow conditions, rather than moving to points with more suitable conditions. Shoal size tended to be reduced during and after elevated discharge, although variability between replicates was high. Small groups of fish tended to break off during the high flow events.
Growth and multiplication of white skeletal muscle fibres in carp larvae in relation to somatic growth rate
Authors: Alami‐Durante H. , Fauconneau B. , Rouel M. , Escaffre A. M. , Bergot P.
Published: April 2005

A morphometric analysis of white axial muscle of common carp Cyprinus carpio was undertaken in order to quantify increase in fibre size, fibre nuclei and fibre number in relation to somatic growth rate during early life. In fast‐growing carp larvae fed zooplankton, length and height of fibres from the central part of dorsolateral muscle increased at the same rate (0.75) relative to the total length of the larvae during the first 2 weeks of feeding. During this period, the number of nuclei per fibre increased threefold while the number of nuclei per unit fibre surface remained constant. In fast‐growing larvae fed a formulated diet, the total cross‐sectional area of one epaxial quadrant of white muscle and the total area of white fibres increased at almost the same rate (3.15; 3.23) relative to larval total length during the first 28 days of exogenous feeding. The total number of white fibres increased faster (2.07) relative to the total length of larvae than the mean area of white fibres (1.16). Hyperplasia accounted for 64% of muscle growth in these larvae. The proportion of fibres with a width < 10 μm decreased from 72% at first feeding to 14% 28 days later, while the proportion of fibres with a width >20 μm which was 0% at first feeding increased up to 34% in the same time. The recruitment of new white fibres seemed to be almost the same in the whole muscle quadrant at first feeding and 18 or 28 days later but, 8 days after first feeding, a transient significant recruitment of new fibres was shown at the apex of the myotome. Comparisons between fast‐ and slow‐growing groups of larvae showed that for a given larval total length: (1) the mean width of central white fibres was higher and the proportion of central fibres with a width <10 μm was lower in slow‐growing larvae than in fast‐growing ones; (2) the total number of white fibres was lower for a higher total cross‐sectional area of white muscle in slow‐growing larvae than in fast‐growing ones. These results suggest that, in Cyprinus carpio larvae, slow‐growing conditions are related to a decreased contribution of hyperplasia to muscle growth.
Larval growth patterns in Cyprinus carpio and Clarias gariepinus with attention to the finfold
Authors: van Snik G. M. J. , van den Boogaart J. G. M. , Osse J. W. M.
Published: April 2005

During the larval period, most teleost fishes undergo a dramatic change in body form. Most functional systems are incomplete at hatching. Rapid development of swimming, feeding and respiration systems are expected. In this study, growth patterns of morphological characteristics related to these three functions were studied in two species of Ostariophysian teleosts: African catfish Clarias gariepinus and common carp Cyprinus carpio. Special attention was paid to the larval finfold, which is a remarkably common feature of fish larvae. The results confirmed that larval growth shows different phases. Many morphological characters showed fast allometric growth in early larvae, followed by isometric growth after an inflexion point. In carp, all larval growth curves showed such inflexion points at a total length of about 7 mm while in Clarias such a coupling was not found. The inflexion points in carp occur at a stage during which the typical larval swimming style changes towards the adult swimming style.
A hermaphroditic Arctic charr from Loch Rannoch, Scotland
Authors: Fraser D.
Published: April 2005

An individual Arctic charr from Loch Rannoch was found to contain a gonad the anterior portion of which consisted of ovarian tissue. This is an extremely rare condition in salmonid fish and in this instance is possibly the result of environmental contamination.
Reproductive biology and endocrine regulation of final oocyte maturation of captive white bass
Authors: Mylonas C. C. , Magnus Y. , Klebanov Y. , Gissis A. , Zohar Y.
Published: April 2005

The ovarian development, and plasma levels of gonadotropin II (GtH II) and sex‐steroid hormones at the end of vitellogenesis were examined in captive white bass Morone chrysops. The changes in plasma hormone levels and oocyte morphology associated with gonadotropinreleasing hormone agonist (GnRHa)‐induced final oocyte maturation (FOM) were studied. Although plasma 17β‐oestradiol (E2) and oocyte diameter increased, there were no changes in GtH II, testosterone (T), 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P) or 17,20β,21‐dihydroxy‐4‐pregnen‐3‐one (17,20β,21‐P) in non‐hormone‐treated females, and no FOM was observed. Treatment with a sustained‐release GnRHa delivery system (GnRHa implant) induced two FOM cycles separated by about 24 h, with the release of approximately equal numbers of eggs in each spawn. Plasma GtH II levels were elevated significantly throughout FOM, reaching a maximum of 9·07 ± 1·55 ng ml−1 in ovulated fish. Both plasma E2 and T increased soon after the GnRHa treatment, but E2 declined in fish undergoing germinal vesicle (GV) migration. Plasma T increased further during FOM (7·55 ± 2·87 ng ml−1), but declined precipitously at ovulation. A surge in plasma 17,20β‐P and 17,20β,21‐P (4·11 ± 0·97 ng ml−1 and 3·10 ± 0·77 ng ml−1, respectively) was observed in females undergoing GV breakdown (GVBD). Based on the involvement of different sex‐steroid hormones, FOM was separated into two stages. Early FOM included lipid‐droplet coalescence and GV migration, and was associated with elevations in plasma GtH II and T. Late FOM included GVBD and yolk‐globule coalescence, and was associated with elevations in plasma GtH II, 17,20β‐P and 17,20β,21‐P. The results of this study point to the absence of a surge in plasma GtH II as the missing link in the reproductive axis responsible for the failure of captive white bass to undergo FOM at the end of vitellogenesis. Sustained elevation of plasma GtH II via treatment with a GnRHa implant induced two consecutive spawns with an overall egg production two‐ to eightfold higher than previously obtained from captive broodstocks, and similar to annual egg production Values reported for wild fish.
Upstream migration of adult Atlantic salmon past a fish counter weir in the Aberdeenshire Dee, Scotland
Authors: Smith I. P. , Johnstone A. D. F. , Smith G. W.
Published: April 2005

During their upstream migration through the lower reaches of the Aberdeenshire Dee, Scotland, radio‐tagged adult Atlantic salmon passed a Crump weir‐based fish counter without substantial delay over a range of river flows and water temperatures. Tagged salmon were detected sequentially by automatic listening stations placed along the river and were detected at the counter site for a median time of 18 min, compared with a median time of 5 min before the weir was built. One fish out of 16 spent 6·7 h in the vicinity of the weir, but such migratory pauses also occurred before the weir existed. The results suggest that the number of salmon crossing the counter per unit time is a function of the number of fish present downstream and their tendency to migrate upstream, without being limited by their ability to surmount the weir. The apparent slight delay at the weir is probably insignificant in terms of the overall progress of riverine migration and in the context of using counter records to relate salmon movements to environmental Variables.
Seasonal patterns of growth, lipid deposition and lipid depletion in anadromous Arctic charr
Authors: Jøsrgensen E. H. , Johansen S. J. S. , Jobling M.
Published: April 2005

Seasonal patterns of growth, lipid deposition and lipid depletion were studied in anadromous Arctic charr from a north Norwegian population. Samples were collected in late May when fish were migrating between fresh water and the sea, and in mid‐July when the fish re‐entered fresh water. A sample of maturing fish captured in mid‐July was held in captivity until late September to assess lipid mobilization linked to the final stages of maturation. The fish increased substantially in weight during their 40–50‐day summer residence in sea water (immatures from c. 300 to 600 g; maturing fish from c. 500 to 800 g), and body lipid stores were increased approximately fivefold. The carcass (head, skeleton and skin) was the major lipid depot, accounting for c. 50% of the total lipid content when the fish re‐entered fresh water from the sea. The muscle of the ascending charr contained 35–40% of the body lipids, whereas the gut and liver each held 4–5%. Body lipid decreased 30–40% during the period between the re‐entry of the fish to fresh water and spawning; although lipids were depleted from all depots the carcass and muscle were quantitatively the most important. By the time of spawning, the gonads of the females held almost 25% of the body lipid, whereas in the males the gonads accounted for <3% of the total lipids. Females lost c. 80% of their body lipid during spawning and overwintering, and, consequently, the lipid depots were severely depleted by the early spring. By contrast, lipid depletion in the males amounted to 50–55% of total lipid in the same period. These data suggest that the combination of spawning and overwintering in fresh water imposes a greater load on the females than on the males. It may be that the severity of the depletion prevents females from spawning in successive years.
Stimulation of testicular function by exogenous testosterone in male protandrous black porgy, Acanthopagrus schlegeli
Authors: Lau E.‐L. , Lin B.‐Y. , Lee F.‐Y. , Sun L.‐T. , Dufour S. , Chang C.‐F.
Published: April 2005

When 4 mg of testosterone (T) per kg food was given to 1‐year‐old protandrous male black porgy Acanthopagrus schlegeli for 7 months, gonadosomatic index was significantly higher than when the dose was 0.5 mg kg−1 food. Both doses of T prolonged the spawning season, and increased the number of spermiating fish and milt volume. Sperm concentrations were similar in spermiating black porgy from the treated and control groups. Low levels of oestradiol‐17β were observed during the experimental period while elevated levels of plasma T were observed only in March in both control and T‐treated groups. Significantly higher levels of plasma 11‐ketotestosterone (11‐KT) were observed in the 0.5‐ and 4.0‐mg T‐treated groups during the spawning season as compared to the control group. The present data suggest that both 0.5‐ and 4·0‐mg T doses stimulate testicular weight, increase numbers of spermiating males and milt volume without affecting the sperm concentrations. Plasma 11‐KT concentrations were elevated during T treatment and closely correlated with testicular development and spermiation.
Feeding behaviour of reared and wild cod and the effect of learning: two strategies of feeding on the two‐spotted goby
Authors: Steingrund P. , Fernö A.
Published: April 2005

This study investigates possible differences in the feeding behaviour of reared and wild cod Gadus morhua and the effect of learning in connection with sea‐ranching experiments. In two laboratory experiments, single individuals, reared or wild, were allowed to prey upon 15 two‐spotted gobies Gobiusculus flavescens in trials of 30 min duration. Reared and wild cod seldom attacked stationary gobies and generally attacked moving gobies, and reaction times were similar (c. 0·25 s). Reared and wild cod ingested similar numbers of gobies per trial. Reared cod, however, caught more gobies in pursuits, while wild cod took more gobies in lunges. Reared cod had higher costs as measured by a higher index of energy expenditure and a higher opercular beat frequency, and wild cod were thus more efficient (benefit divided by cost). The efficiency of both groups tended to increase as they gained experience. The results indicate that reared cod more often used a pursuit strategy and wild cod more often a lunge strategy. Differences in previous experience may have initiated the strategies, and the success of each strategy in the experimental situation, in addition to the potential cost of changing strategy, may have maintained them. For cod released into a natural habitat, a pursuit strategy may lead to low efficiency vis‐à‐vis mobile prey and could also involve a high risk of predation, forcing reared Cod to change strategy.
Validation of daily increment formation in otoliths for three Diplodus species in the Mediterranean sea
Authors: Vigliola L.
Published: April 2005

The efficacy of two fluorochromes, chlorhydrate of tetracycline (CHTC) and alizarin complexone (ALC), to induce a label on the otoliths of juvenile sparid fishes by immersion techniques was tested in different experimental conditions. CHTC did not mark otoliths in natural sea water and was toxic in divalent cation‐free sea water. Immersing fish in a 50‐mg 1−1 ALC natural seawater solution for 24 h induced a well‐defined mark on the otoliths and had no effect on survival. A daily periodicity of increment formation on otoliths was observed in captivity for Diplodus vulgaris and D. puntazzo, and was conserved in natural environment for D. sargus. The frequency of increment deposition did not vary with the age of juvenile fishes. Thus, otolith microstructure analysis will be a reliable method to give age estimates in these three sparid species during their juvenile life.
Sensory development and concurrent behavioural changes in Atlantic croaker larvae
Authors: Poling K. R. , Fuiman L. A.
Published: April 2005

Development of the visual and mechanosensory systems of Atlantic croaker larvae was examined and compared to behavioural performance in order to determine sensory system functionality. Early larvae were characterized by a photopic visual system with a high density of cone photoreceptors, but no rods or photoreceptor summation on to higher order cells. Acuity of small larvae was comparable to other species. The mechanosensory system of early larvae consisted of a relatively high density of free neuromasts on the head and body. By approximately 10 mm total length (LT), many sensory attributes of larvae had changed. Visual acuity had improved to levels slightly better than in other species. Rods began forming and summation ratios increased, indicating development of scotopic vision. Cephalic lateral‐line canals began to enclose at 15 mm LT and were complete by 24 mm. The trunk lateral‐line began to enclose at 30 mm and was complete by 40 mm. Behavioural performance was tested using an artificial predatory stimulus under different conditions to isolate the roles of vision and mechanoreception. Both sensory systems were necessary to elicit the highest levels of responsiveness. Responsiveness of larvae <6mm was equally influenced by visual and neuromast input, while responsiveness of larvae > 6 mm was largely influenced by visual input. Both vision and mechanoreception influenced ontogenetic changes in reactive distance of larvae. When there was no visual input, reactive distances increased slightly through ontogeny, indicating the use of mechanoreception. Only when mechanoreception was blocked, the ontogenetic increase in reactive distances was greater than that of larvae with all sensory systems intact. These results indicate that Atlantic croaker larvae use both sensory systems throughout the larval period, but the relative importance of these sensory systems changes with ontogeny.
Effects of kinship on aggression and RNA content in juvenile Arctic charr
Authors: Olsén K. H. , JäUrvi T.
Published: April 2005

The behaviour of juvenile Arctic charr Salvelinus alpinus was studied in groups of four siblings composed of familiar and unfamiliar individuals or in mixed groups of four where both siblings and unrelated individuals were present. The frequency of aggressive acts was significantly higher in the mixed groups compared to the pure sibling groups and the difference was present at all levels of the hierarchy rank order, based on a dominance index, except the lowest ranked individuals. The difference was significant after but not before feeding, implying that competition with non‐kin for a food resource increased the aggression. No significant difference in weight gain was observed between sibling and mixed groups during the 6 days of the experiment, but the RNA contents of lateral musculature in dominant individuals from sibling groups were significantly higher than the corresponding fish in the mixed group, suggesting a difference in growth rate when the experiments ended. No significant difference in RNA content was observed between subordinate fish of the two treatments, i.e. siblings v. mixed.
Basking shark occurrence off south‐west England in relation to zooplankton abundance
Authors: Sims D. W. , Fox A. M. , Merrett D. A.
Published: April 2005

Basking sharks Cetorhinus maximus >3 m total length arrived off Plymouth, U.K. directly after the increase in zooplankton density in May, while young‐of‐the‐year basking sharks (<3 m) occurred when zooplankton density was lower (0·8‐1·1 g m−3). No basking sharks were seen after July when the zooplankton density was least.
Age estimation of the exploited deepwater shark Centrophorus squamosus from the continental slopes of the Rockall Trough and Porcupine Bank
Authors: Clarke M. W. , Connolly P. L. , Bracken J. J.
Published: April 2005

Dorsal spine sections of the deepwater squalid shark Centrophorus squamosus provided age estimates of 21–70 years. Small specimens were not recorded in the study area. It was not possible to obtain estimates from vertebral centra. The estimates are discussed in the context of other studies using dorsal spines of squalid sharks. Sexual maturity was achieved at large size, >75% of maximum length. Total length at 50% maturity was calculated as 101 cm (males) and 128 cm (females).
Modelling changes in migration pattern of herring: collective behaviour and numerical domination
Authors: Huse G. , Railsback S. , Feronö A.
Published: April 2005

According to the adopted‐migrant hypothesis, first time spawning herring Clupea harengus learn their migration pattern from schooling with older individuals. Changes in migration pattern of Norwegian spring‐spawning herring co‐occur with the recruitment of abundant year classes to the spawning stock. It is argued that this is due to the abundant year classes being unable to learn from the older ones since most of the recruiting year class only experience their own naïve class‐mates. An individual‐based school simulation study is presented to explore the hypothesis. Behaviour is simulated using individual rules that take into account the movements of nearby individuals. After establishing a schooling pattern, a small proportion of the individuals is directed to move towards a given position while the remaining individuals keep using their behaviour rules. When <4% of the individuals are so directed there is no response seen in the remaining school. But when ≥7% of the total school is directed to a specific location, the remaining individuals always respond and follow the directed individuals. The simulations thus show that determined individuals can have a substantial influence on the collective behaviour of schools. Furthermore, the knife‐edge response in school behaviour suggests that the relative abundance of determined individuals in a school plays an important part in the collective behaviour. This mechanism can explain the observed changes in migration pattern of Norwegian spring‐spawning herring associated with the recruitment of abundant year classes to the adult Stock.
Fish community structure in mesotrophic and eutrophic lakes of southern Finland: the relative abundances of percids and cyprinids along a trophic gradient
Authors: Olin M. , Rask M. , Ruuhljärvi J. , Kurkilahti M. , Ala‐Opas P. , Ylönen O.
Published: April 2005

In 36 south Finnish lakes, the number of species, as well as the cyprinids:percids ratio, was dependent, not only on total phosphorus (TP), but also on lake size. Total fish biomass and cyprinid biomass increased along the TP gradient, whereas the dependence of percid biomass was less evident. Perch Perca fluviatilis and roach Rutilus rutilus strongly dominated mesotrophic lakes; in eutrophic lakes the proportion of other cyprinids and percids, such as white bream Blicca bjoerkna, bream Abramis brama, pikeperch Stizostedion lucioperca and ruffe Gymnocephalus cernuus, increased. Perch biomass was weakly related to abiotic factors but depended on roach biomass. Lake size and fish species composition are essential factors affecting fish community changes in relation to TP, and may be important as well in regulating the responses of a fish community to biomanipulation.
The role of F‐series prostaglandins as reproductive priming pheromones in the brown trout
Authors: Moore A. , Olsén K. H. , Lower N. , Kindahl H.
Published: April 2005

Electrophysiological studies demonstrated that the olfactory epithelium of mature male brown trout Salmo trutta parr was acutely sensitive to F‐series prostaglandins (PGFs) PGF1α and PGF2α, with detection threshold concentrations of 10−11 M. The olfactory epithelium was also sensitive to the PGF metabolite 15‐ketoPGF2α (threshold 10−8 m), but did not detect a further metabolite, 13,14,‐dihydro‐15‐ketoPGF2α Immature brown trout did not detect any of the prostaglandins tested. Exposure of mature male brown trout parr to waterborne PGF1α and PGF2α (concentration 10−8 m), resulted in significant increases in levels of expressible milt and the plasma concentrations of 17,20β‐dihydroxy‐4‐pregnen‐3‐one, testosterone and 11‐ketotestosterone. The olfactory epithelium of both immature and mature male brown trout parr was sensitive to the urine and ovarian fluid from ovulated female brown trout. Exposure of mature male brown trout parr to ovarian fluid resulted in an increase in the levels of plasma 17,20β‐dihydroxy‐4‐pregnen‐3‐one whilst exposure to urine increased the levels of expressible milt. In addition, PGF2α was found to be present within both the urine and ovarian fluid of mature female brown trout. It is suggested that the F‐series prostaglandins have a role as priming pheromones in male brown trout.
Treatment with an aromatase inhibitor suppresses high‐temperature feminization of genetic male (YY) Nile tilapia
Authors: Kwon J. Y. , McAndrew B. J. , Penman D. J.
Published: April 2005

High temperature (36° C) treatment during sexual differentiation caused significant changes in sex ratio in YY male Nile tilapia Oreochromis niloticus fry (64.5% males compared to 100.0% males at 28° C), while dietary treatment with a chemical aromatase inhibitor (AI: Fadrozole™ CGS16949A) during this period suppressed the high temperature feminization (98.9% males). This implies that cytochrome P450 aromatase is mechanistically associated with temperature‐dependent sex determination (TSD) in this species. XY male fry did not show significant sex reversal at 36° C. In XX female fry, high temperature treatment resulted in significant masculinization (62.5% males compared with 21.9% males at 28° C), while treatment with AI at either temperature resulted in very high proportions of males (100.0% males at 36° C; 99.0% males at 28° C). These results confirm the importance of aromatase in sexual differentiation in the Nile tilapia below the TSD threshold and suggest that it also plays a role in TSD, at least in the YY genotype.
The genetics of maintenance of an all‐male lineage in the Squalius albuvnoides complex
Authors: Alves M. J. , Collares‐Pereira M. J. , Dowling T. E. , Coelho M. M.
Published: April 2005

Squalius alburnoides is a complex of minnows common to the Iberian Peninsula, consisting of two distinct forms. The most common form is comprised of diploid and polyploid asexual hybrids heterozygous for several diagnostic allozyme loci contributed by Squalius pyrenaicus or Squalius carolitertii and a missing ancestor. The other form is diploid and homozygous for the allele contributed by the missing ancestor at these same loci. Present results from analyses of sex ratio and cytochrome b sequences are not consistent with the evolutionary distinctiveness of this non‐hybrid form and suggest that it represents an all‐male lineage imbedded within an almost all‐female complex. This all‐male lineage allowed preservation of the ancestral paternal nuclear genome after the paternal ancestor became extinct in all or most drainages, withimportant evolutionary implications.
Infection of the gonads of Glaucosoma hebvaicum by the nematode Philometva lateolabracis: occurrence and host response
Authors: Hesp S. A. , Hobbs R. P. , Potter I. C.
Published: April 2005

The prevalence of infection of the West Australian dhufish Glaucosoma hebraicum off the lower west coast of Australia by Philometra lateolabracis was greater among females than males, which contrasts with the situation with Pagrus auratus in waters off New Zealand. Live P. lateolabracis were represented solely by females and were found only in the gonads of fish of mature size (L50 at first maturity = c. 300 mm) caught between December and April and thus during the spawning period of dhufish. Since the gonads were largest during that period, they, and particularly ovaries, would provide an abundant food source in the form of blood. The prevalence of the parasite (live + dead individuals) increased with host body size to reach a maximum of c. 80% in the 700–799 mm length class of females and c. 50% in the largest length class of males. During the spawning period of G hebraicum, P. lateolabracis developed from small, non‐gravid females to large gravid females, representing an increase in mass of more than 200 times. The maximum length of P. lateolabracis (470 mm) in G hebraicum is the greatest yet recorded for this species. Gonadosomatic indices provided no evidence that infection by P. lateolabracis leads to a conspicuous atrophy of the ovaries, which contrasts with the situation with the gonads of some of the teleosts infected by Philometra species, and presumably reflects, in part, the small volume of the ovary occupied by P. lateolabracis (c. 3%) and the low intensity of infection (mean = 2.0, maximum = 7). Although the presence of live P. lateolabracis did not stimulate an obvious tissue response by the ovaries during the spawning period of G. hebraicum, both the dead and any live parasites that remain after spawning become encapsulated in fibrous tissue.
The influence of life‐history strategy on lipid metabolism in overwintering juvenile Atlantic salmon
Authors: Morgan I. J. , McCarthy I. D. , Metcalfe N. B.
Published: April 2005

From November to May, the lipid mass in the viscera and carcass of juvenile Atlantic salmon Salmo salar that were undergoing smolt transformation prior to seaward migration (‘early migrants’) were significantly greater than those of their siblings that would delay migration for at least a further year. During winter (November‐February), the depletion of lipid associated with the viscera was significantly greater in early migrants, whilst lipid depletion in the remaining carcass was greater in delayed migrants. Early migrants continued to deplete both lipid compartments in spring (February‐May), whereas delayed migrants depleted visceral lipid but replenished carcass lipid over the same period. Fatty acid accumulation rates (a measure of storage lipid synthesis rates) were two to six times greater in visceral than in carcass lipid throughout the study, suggesting that lipid turnover is much more rapid in the viscera. There were no differences in fatty acid accumulation rates between migrant groups in November, despite the much lower food consumption rate of delayed migrants at that time, suggesting that these fish allocated a larger proportion of their nutritional resources to lipid synthesis. In the carcass lipid of early migrants, and in both the visceral and carcass lipid of delayed migrants, the fatty acid accumulation rate was negatively correlated with lipid mass. Fatty acid accumulation rates increased from November to February in both visceral and carcass lipid in the two migrant groups. The fatty acid accumulation rate in carcass lipid was significantly higher in delayed migrants than in early migrants in February, but not in May. These results support the hypothesis that life history strategies involving rapid growth will result in a relatively low allocation of resources to lipid reserves.
Heterosis for neonatal survival in the guppy
Authors: Shikano T. , Taniguchi N.
Published: April 2005

Neonatal survival rate ranged from 91.8 to 100.0% in 12 populations of the guppy Poecilia reticulata, and was higher in naturalized Japanese stream populations than in domestic strains. Mean heterozygosity at five allozyme and four microsatellite loci varied between 0.112 and 0.430 and was significantly correlated with neonatal survival rate among populations, suggest ing that inbreeding decreases neonatal survival. Diallel and reciprocal crosses among four domestic strains demonstrated heterosis for neonatal survival. These results indicate that neonatal survival is genetically affected by heterosis and its antithesis, inbreeding depression. The relationship between neonatal survival and the mean heterozygosity suggests that overall heterozygosity is important for neonatal survival of the guppy.
Resource use by large catfishes in a reservoir: is there evidence for interactive segregation and innate differences?
Authors: Edds D. R. , Matthews W. J. , Gelwick F. P.
Published: April 2005

Blue catfish Ictalurus furcatus and channel catfish Ictalurus punctatus, two large‐bodied piscivore‐omnivores in Lake Texoma, Texas‐Oklahoma, U.S.A., showed very high overlap in food use, but substantial differences in use of habitat during the year. Both species primarily ate fishes, aquatic insects, vegetation and detritus, terrestrial insects, seeds and zooplankton, with overall overlap = 98%. Diet breadth indices were very similar (blue catfish=4.31, channel catfish = 4.53). Quantitative and qualitative feeding varied seasonally and food habits changed ontogenetically. Feeding intensity was greatest in winter and lowest in late summer. Aquatic insects were eaten more from May to October and fishes more in winter. At body sizes from 100 to 299 mm Ls, both species primarily ate aquatic insects, terrestrial insects, fishes or zooplankton, whereas the diets of individuals >300 mm Ls of both species were dominated by fishes. Overall, their overlap in distribution across major habitat types was only 58%, with blue catfish most abundant in deep water offshore, and channel catfish more common in shallow cove habitats. Blue catfish that did occur in coves were in the deeper parts of those habitats, essentially not occurring in the littoral zone. In lakes without blue catfish, channel catfish are widely dispersed in various habitats and it is suspected that displacement of channel catfish by blue catfish may influence habitat differences of the two species in Lake Texoma. Because the spatial separation of the species also reflects their typical interspecific differences in unimpounded drainages, however, the habitat differences observed in Lake Texoma probably also reflect evolved, historical differences in ecology of the two species.
Lake spawning of brown trout related to groundwater influx
Authors: Brabrand Å. , Koestler A. G. , Borgstrøm R.
Published: April 2005

Seepage water through a lake bottom and the layering of tight and high‐permeable layers in the aquifer produce groundwater under greater pressure than the water column of the lake. This results in under‐water springs and seepages. When spawning substrata were available, there was a spatial correlation between the degree of groundwater influx and the redd density of brown trout Salmo trutta. In high density spawning areas with > 100 observed redds ha−1, the mean seepage water influx during spring was c. 1200 ml m−2 min−1 compared to a mean flux of 113 ml m−2 min−1 in low density spawning areas with 5–10 redds ha−1.
Variation in food intake within groups of juvenile perch
Authors: Staffan F. , Magnhagen C. , Alanärä A.
Published: April 2005

The coefficient of variation of individual food intake was large in small groups of young‐of‐the‐year perch Perca fluviatilis (45–60 mm LT) and smaller when fish that were given the same feeding rank were placed together. No aggressive interactions were detected during feeding.
Growth rate correlations across life‐stages in female Atlantic salmon
Authors: Einum S. , Thorstad E. B. , Næsje T. F.
Published: April 2005

Within smolt ages there was a strong negative correlation between pre‐ and post‐smolt growth in wild three‐sea‐winter female Atlantic salmon Salmo salar. This indicates that trait values providing, or resulting from, increased growth in one environment may cause growth to decrease in the other, potentially constraining growth rate evolution.
Advances in the larval rearing of Siberian sturgeon
Authors: Gisbert E. , Williot P.
Published: April 2005

Since first large‐scale attempts to culture sturgeon from the larval stage were carried out in the former U.S.S.R. at the end of the nineteenth century, rearing technology has advanced considerably during the last 20 years and noticeable improvements in incubation and larval rearing techniques have been implemented in normal hatchery procedures. Siberian sturgeon eggs are incubated in MacDonald jars at 13–14° C to prevent fungal infections. Mass hatching takes place 7 days after fertilization and hatching rate can be predicted as a function of the percentage of eggs fertilized. Survival at the end of the endogenous feeding stage is correlated with hatching rate. Egg size has no direct implications for larval growth and survival of Siberian sturgeon. Experimental studies have demonstrated that behavioural observations are useful criteria to assess the quality of larvae and to synchronize the physiological state of fish with the appropriate rearing procedures. Special attention should be given to the transition to exogenous feeding, where cannibalism, difficulties in adaptation to a new diet, overfeeding and resulting bacterial infections dramatically reduces survival to the fingerling stage. Although a commercial artificial diet specifically formulated for larvae of Siberian sturgeon and other acipenserids is still lacking, commercial non‐purified rainbow trout diets and starter marine fish diets are currently used and their results are reasonably acceptable in terms of larval growth and survival. Further research must be focused on the determination of egg quality indicators in order to provide the producer with the tools to estimate the viability and performance of theprogeny.
Complementary left and right eye use during predator inspection and shoal‐mate scrutiny in minnows
Authors: De Santi A. , Bisazza A. , Vallortigara G.
Published: April 2005

Minnows Phoxinus phoxinus did not show any difference in the average distance from a predator associated with the left or right position of a shoal‐mate. While inspection behaviour of fish tested with a mirror on their left side was indistinguishable from the behaviour of controls tested without a mirror, inspection behaviour of fish tested with the mirror on their right side appeared to be changed and incoherent in both temporal and spatial parameters. These results suggest that, as in mosquitofish Gambusia holbrooki, the condition with the mirror on the left provided the best arrangement of monocular lateral stimulation in which each stimulus fell into the correct lateral visual field. Minnows showed a significant left eye preference during scrutiny of their mirror image when tested in the absence of any predator and a significant right eye preference while monitoring a live predator in the absence of a social partner.
Food supplementation increases larval growth, condition and survival of Acanthochromis polyacanthus
Authors: Booth D. , Alquezar R.
Published: April 2005

Supplementary feeding to damselfish Acanthochromis polyacanthus larvae, at One Tree Island on the southern Great Barrier Reef, Australia, led to increased growth in length and enhanced condition relative to unfed control larvae, although both groups dropped in body condition (measured as total lipids) over the experimental period. Survival of fry was enhanced in fed broods, with on average 60% survival over 20 days, compared to 46% survival in unfed broods. Growth, condition and survival were neither density‐dependent nor body‐size dependent within broods. This study suggests variation in food supply may strongly influence persistence of larvae to juvenile stages, and thus influence cohort size.
Influence of activity in a heterogeneous environment on the dynamics of fish growth: an individual‐based model of roacl
Authors: Hölker F. , Breckling B.
Published: April 2005

A spatio‐temporal individual‐based model (IBM), including bioenergetic principles, is used to investigate how energy costs coupled to activity represent a variable fraction in a heterogeneous environment and how this is related to another energetic criterion, the potential individual growth, under the conditions of a structured environment. With this approach, it is possible to connect simulated spatio‐temporal activity patterns with the energetic needs required for these activities. By using simple foraging rules and a modified random walk model it is possible to reproduce spatial distributions and length frequency distributions. The simulated spatial distribution of roach Rutilus rutilus in Lake Belau, Germany, results in a mean weekly activity multiplier [(standard metabolic rate + activity costs) (standard metabolic rate)−1] of 1–9 with deviations >100% during a simulated year. These deviations are of key importance to differences in the growth rate of individual simulated roach.