Showing papers in "Journal of Fish Biology in 1998"
TL;DR: Migratory herbivorous fishes originating from eutrophic, productive ecosystems may subsidize resident predators of oligotrophic river ecosystems, which may result in cascading direct and indirect eVects on other species in local food webs.
Abstract: Tropical rivers and their associated floodplain habitats are dynamic habitat mosaics to which fishes are challenged to respond in an adaptive manner. Migratory fishes create linkages among food webs that are partitioned along a nested hierarchy of spatial scales. Such linkages are examined across a hierarchy of spatio-temporal scales, ranging from small streams to entire drainage basins, for rivers in South America and Africa. Migratory herbivorous fishes originating from eutrophic, productive ecosystems may subsidize resident predators of oligotrophic river ecosystems, which may result in cascading direct and indirect eVects on other species in local food webs. Successful management of many of the most important stocks of tropical river fishes requires conceptual models of how fish movement influences food web structure and dynamics.
449 citations
TL;DR: Results reveal that the viability of cod larvae is related to attributes of the spawning females and that this information is important to the authors' understanding of stock‐recruitment relationships.
Abstract: Size, condition, and age of female-Icelandic cod Gadus morhua were correlated to the size of their eggs and newly hatched larvae. A positive relationship was detected between egg size and some larval viability parameters, including the age at first feeding, successful development of a swimbladder, and specific growth rates during the first 15 days after hatching. These results reveal that the viability of cod larvae is related to attributes of the spawning females and that this information is important to our understanding of stock‐recruitment relationships. ? 1998 The Fisheries Society of the British Isles
346 citations
TL;DR: The logarithm of oxygen consumption rate, and the tail beat frequency of solitary swimming sea bass, were each correlated linearly with swimming speed, and also with one another.
Abstract: Tail beat frequency of sea bass, Dicentrarchus labrax (L.) (23.5 ± 0·5 cm, LT), swimming at the front of a school was significantly higher than when swimming at the rear, for all water velocities tested from 14·8 to 32 cm s−1. The logarithm of oxygen consumption rate, and the tail beat frequency of solitary swimming sea bass (28·8 ± 0·4 cm, LT), were each correlated linearly with swimming speed, and also with one another. The tail beat frequency of individual fish was 9–14% lower when at the rear of a school than when at the front, corresponding to a 9–23% reduction in oxygen consumption rate.
236 citations
TL;DR: This study shows that individual differences in standard metabolic rate (SMR) may contribute to differences in aggression between juvenile Atlantic salmon, and that although mean growth was not improved in the low SMR group by excluding high SMR fish, their growth subsequently showed less variability.
Abstract: In aquaculture, competitive interactions for food are a major source of growth rate variation, since they result in aggressive individuals acquiring a disproportionate amount of food and growing faster. Consequently, such competition increases the variance and skew of the size distribution of fish. In Atlantic salmon Salmo salar acquaculture, rearing is often initiated with juveniles of uniform size. However, the initial factors allowing fish to out-compete others of the same size is unclear. This study shows that individual differences in standard metabolic rate (SMR) may contribute to differences in aggression between juvenile Atlantic salmon. Fish were segregated into three holding tanks on the basis of differences in relative SMR aggression was highest in the tank containing high SMR fish, and lowest in a low SMR group. However, there were no significant differences in mean growth between the three treatments, although the skew of the size distribution was much less in the low SMR group than in the high SMR group. Therefore, although mean growth was not improved in the low SMR group by excluding high SMR fish, their growth subsequently showed less variability, possibly as a consequence of fewer despotic individuals gaining disproportionate access to food.
215 citations
TL;DR: Case studies from endangered populations of topminnows from North American deserts are used to illustrate a variety of methods used in conservation genetic studies.
Abstract: Genetic markers have helped to resolve many diYcult taxonomic problems and map patterns of diversity within and among remnant populations of threatened and endangered species. Knowledge of historical patterns of gene flow can help to manage dispersal among anthropogenically fragmented populations. Genetic considerations are used in the design of captive breeding programmes that avoid inbreeding depression and artificial selection that may impact on Darwinian fitness. Case studies from endangered populations of topminnows from North American deserts are used to illustrate a variety of methods used in conservation genetic studies. Several merits of studying putatively neutral, molecular markers v. adaptive phenotypic traits are discussed. ? 1998 The Fisheries Society of the British Isles
184 citations
TL;DR: In spatial competition between individuals, neither fish sex nor body mass affected dominance status in masu salmon Oncorhynchus masou, but resting metabolic rate was significantly correlated with dominance status, indicating that a high metabolic rate can increase the dominance rank of juvenile salmon.
Abstract: In spatial competition between individuals, neither fish sex nor body mass affected dominance status in masu salmon Oncorhynchus masou In contrast, resting metabolic rate (MR) was significantly correlated with dominance status, indicating that a high metabolic rate can increase the dominance rank of juvenile salmon Whole animal growth rate was significantly correlated with MR, but not with initial body weight This suggests that the body size of masu salmon is not a cause, but rather a consequence, of dominance status which is closely related to MR The increment width between otolith daily rings was also significantly correlated with MR Thus, the size of the Otolith may indicate the degree of MR
177 citations
TL;DR: The study validates that the Ecosim model can be used to predict ecosystem level changes following changes in fishing pressure, therefore fishing induced changes can to a large extent explain the changes in ecosystem pools and fluxes observed over time.
Abstract: Two mass-balance trophic models are constructed to describe the Gulf of Thailand ecosystem (10–50 m depth): one model pertains to the initial phase of fisheries development, and the other to when the resources were severely depleted. The two phases are compared, and changes brought about by fishing discussed. A dynamic simulation model, Ecosim, is then used successfully to reproduce the 1980 state of the fishery based on the 1963 model and the development in catches. In addition the 1980 model is used to predict how the ecosystem groups may bounce back following marked reduction in fishing pressure. Finally, the 1963 model is used to study alternative scenarios for how the fisheries development could take place, notably the effect of exploiting only the resources of larger species. The study validates that the Ecosim model can be used to predict ecosystem level changes following changes in fishing pressure, therefore fishing induced changes can to a large extent explain the changes in ecosystem pools and fluxes observed over time.
172 citations
TL;DR: Common snook Centropomus undecimalis were sampled monthly from the Jupiter–Lake Worth area of Florida's Atlantic coast during 1989 and 1991 and from Tampa Bay on Florida's Gulf of Mexico coast during 1988 and 1989 and group-synchronous oocyte development was demonstrated.
Abstract: Common snook Centropomus undecimaliswere sampled monthly from the Jupiter–Lake Worth area of Florida's Atlantic coast during 1989 and 1991 (1452 fish) and from Tampa Bay on Florida's Gulf of Mexico coast during 1988 and 1989 (2090 fish). Group-synchronous oocyte development was demonstrated. Ovarian maturation began during March or April on both coasts. Spawning was first detected histologically in April during 1989 and 1991 on the Atlantic coast and during May in 1988 and in April in 1989 on the Gulf coast. In each year, spawning ended during October on the Atlantic coast and during September on the Gulf coast. Ovarian histological evidence suggested that individual females may spawn every 1·1–2·5 days between 1400 and about 2000 hours. Final oocyte maturation occurred independently of either tidal cycle or lunar phase, and some common snook were observed in prespawning or spawning condition on every day sampled. Spawning occurred in or near major inlets to the Atlantic Ocean and the Gulf of Mexico, in secondary passes to larger inland bays and bayous, and around nearshore islands.
162 citations
TL;DR: It can be assumed that the primary function of this nocturnal behaviour during winter is most likely to hide from diurnal predators.
Abstract: During winter, juvenile Atlantic salmon Salmo salar become nocturnal and seek refuge during the day in the stream bed gravel interstitial spaces. The function of this behaviour is unclear, but two major types of hypothesis have been proposed. One is that the fish are hiding from something (e.g. a predator) and the other is that the fish are seeking shelter from the water current. These hypotheses were tested by examining the selection of juvenile salmon for refuges that offered different degrees of concealment or shelter. The fish clearly preferred refuges that allowed them to hide (i.e. they were dark and opaque) but offered little shelter from the current. Therefore, it can be assumed that the primary function of this nocturnal behaviour during winter is most likely to hide from diurnal predators.
162 citations
TL;DR: The winter period put considerable stress on the young salmonids living in lotic environments, in particular for the smallest fry with the lowest energy content before winter and the largest losses during winter, which should make the fry more vulnerable to adverse abiotic and biotic factors.
Abstract: The body composition of protein and fat in Atlantic salmon Salmo salar and brown trout Salmo trutta before and after winter was investigated in a temperate, small river, normally ice covered from the middle of November until the end of March. Fat, protein and specific energy declined greatly in winter but were replenished rapidly in spring. Rates of decline were slower for the smallest fish, which also had the lowest specific content of fat, protein, and energy, while the differences in absolute amounts were greatest for the largest fish. The mean specific fat content was reduced by 45–70% during winter, relative to the pre-winter period (September). Mean daily reductions in specific enegy of the larger size groups of brown trout (3·7 × 10−3 kJ g−1 day−1) were almost half of the corresponding values for the largest Atlantic salmon (6·3 × 10−3 kJ g−1 day−1) during winter. A minor reduction in protein content was found during winter, with mean reductions of 6–10% in comparison to those in September. During spring the fat content was replenished rapidly, particularly for the smallest salmon fry (a threefold increase from April to June). Fat content in the larger salmon and trout increased by about 1·8 times. Based on estimated metabolic rates, digested energy during wintertime may contribute about two-thirds of the brown trout fry's energy demand. For Atlantic salmon, the corresponding value is about 50%. The winter period put considerable stress on the young salmonids living in lotic environments, in particular for the smallest fry with the lowest energy content before winter and the largest losses during winter. This should make the fry more vulnerable to adverse abiotic and biotic factors.
152 citations
TL;DR: A mechanism for lobular growth during early, mid-, and late maturation is presented; and it is hypothesized that a permanent germinal epithelium first appeared in the fishes.
Abstract: During the annual reproductive cycle, the lobular testis of Centropomus undecimalis undergoes height, width, and morphological changes which reflect five reproductive classes: regressed; early, mid-, and late maturation; and regression. Histological criteria, particularly differences between continuous and discontinuous germinal epithelia, are used to distinguish these five classes, even though they are only reference points within the annual gonadal cycle. A mechanism for lobular growth during early, mid-, and late maturation is presented; and it is hypothesized that a permanent germinal epithelium first appeared in the fishes. Throughout the year, periodic acid-Schiff-positive macro-melanophage centres and PAS-positive granulocytes are observed in the testis. They are most abundant after the breeding season, and they may be involved in focal tissue degradation.
TL;DR: The results of a multivariate and univariate morphometric analysis of three groups of Arctic charr Salvelinus alpinus from Loch Rannoch, Perthshire, Scotland, distinguished a priori on the basis of coloration and site of capture, producing a clear and highly significant distinction between brightly and cryptically coloured charr.
Abstract: This paper describes the results of a multivariate and univariate morphometric analysis of three groups of Arctic charr Salvelinus alpinus from Loch Rannoch, Perthshire, Scotland, distinguished a priori on the basis of coloration (bright v. cryptic) and site of capture (from two locations 12 km apart). The analysis produced a clear and highly significant distinction, not only between brightly and cryptically coloured charr, but also between the two cryptically coloured groups, one of which was more robust in terms of several size-independent head measurements. Stomach analysis showed that the brightly coloured charr fed entirely on zooplankton, the less robust, cryptically coloured fish, fed on benthic macroinvertebrates, whereas a significant proportion of the diet of the more robust cryptically-coloured form consisted of other fish. DiVerences in length at age also distinguished the three forms, with the robust, piscivorous charr, which live longer and potentially reach a larger final size, attaining smaller sizes at a given age. These data clearly confirm the previous identification of a distinct planktivorous morph of Arctic charr in Loch Rannoch and extend the morph analysis by distinguishing two additional morphs, a benthivorous morph and a piscivorous morph that are morphologically and ecologically distinct. The results are discussed in the context of other systems in which sympatric morphs of Arctic charr have been described. ? 1998 The Fisheries Society of the British Isles
TL;DR: The most sensitive sperm : ova ratio for monitoring pollutant effects on fertilization success was 1500 : 1, which corresponds to half the minimal amount that yields a high fertilization rate in artificial insemination.
Abstract: The optimal ratio of spermatozoa : egg (15 000 : 1) for artificial insemination of African catfish Clarias gariepinus gave fertilization and hatching rates of 80 and 67%, respectively. Below a sperm : ova of 3000 : 1 fertilization success decreased significantly. Excessive sperm (>15 000 : 1) partly inhibited fertilization success. Sperm motility was decreased significantly by 0·001 mg 1−1 Hg2+ as HgCl2, but its effect on fertilization was dependent on the sperm : ova ratio, since excess sperm masked the effect of the pollutant. The most sensitive sperm : ova ratio for monitoring pollutant effects on fertilization success was 1500 : 1, which corresponds to half the minimal amount that yields a high fertilization rate in artificial insemination. There was a good correlation between fertilization and hatching rates (r=0·83; P<0·05). Although both fertilization and hatching rates provide equally good indicators of fertilization success, the more rapid fertilization rate test is recommended since it requires only 12 h.
TL;DR: The data suggest that the retention of fish in keepnets following capture, does not represent a source of stress additional to that imposed by capture and has no effect on the rate of recovery of the fish from the initial capture stress.
Abstract: Capture of carp from holding tanks by dip-net, or from semi-natural conditions by rod and line, elicits a physiological stress response characterised by elevation of plasma cortisol levels. The transfer of carp to keepnets subsequent to capture does not increase or reduce the magnitude or duration of this response and in both cases plasma cortisol levels have returned to pre-stress levels within 24 hours of the initial disturbance. The post-capture plasma cortisol elevation is accompanied by disturbances in plasma glucose and lactate levels but these are less consistent in severity and duration than the cortisol response. These data suggest that the retention of fish in keepnets following capture, does not represent a source of stress additional to that imposed by capture and has no effect on the rate of recovery of the fish from the initial capture stress.
TL;DR: A generalized model of cichlid adaptive radiation is derived, defined by the most influential habitat characteristics and interactions among members of the species community at each phase, in an attempt to provide an explicit hypothesis for a dynamic evolutionary process.
Abstract: In the African cichlid species flocks several corresponding ecotypes and species communities have evolved independently in each of the lakes. These flocks can be viewed as reiterations of a process, induced by the same type of external event (the formation of a lake) and seeded by the same group of organisms, equipped with the same innovative potential. The East African lakes differ in their ages, so that different stages of adaptive radiation of a single group of fishes can be studied simultaneously. This review combines findings on various African cichlid species flocks and derives a generalized model of cichlid adaptive radiation. The model constitutes four stages, defined by the most influential habitat characteristics and interactions among members of the species community at each phase. It is an attempt to provide an explicit hypothesis for a dynamic evolutionary process, as a basis to future studies.
TL;DR: This theory, based on the author's earlier work, is built around the notion that gill area severely constrains the respiration and hence the growth of fishes (and other water-breathing animals).
Abstract: When key biological statistics (growth parameters, mortality rates, etc.) of a large number of fish species are plotted against other variables (notably maximum size and mean habitat temperature), clear trends or patterns tend to emerge. These patterns are usually not perceived as requiring explanation, as reflected in the rarity of pertinent hypotheses in the literature, relative to the ubiquity of the patterns. A theory is presented which has the potential to explain the propensities behind many of these observed patterns. This theory, based on the author's earlier work, is built around the notion that gill area severely constrains the respiration and hence the growth of fishes (and other water-breathing animals). The patterns generated by growth-related processes, such as mortality, reproduction or food consumption can then also be explained. In this theory, tropical fishes are not different from other fishes, once account is taken of the fact that tropical fish are, not metaphorically but literally, in hot water.
TL;DR: Reproductive activity was noted practically throughout the year with its most pronounced spawning peak in the autumn, suggesting that spawning occurred in autumn/winter at the edge of the shelf.
Abstract: The bathymetric distribution of Merluccius merluccius was studied as a function of length, age and maturity of specimens caught by commercial trawl and longline in diVerent seasons. Males matured first at 28·8 cm (3 years old), and females at 38·0 cm (3·5 years old). Reproductive activity was noted practically throughout the year with its most pronounced spawning peak in the autumn. Most fish 46 cm were females. Specimens occurred between 50 and 750 m depth, although density was low at >400 m. Adults were found at all depth strata studied. Recruits and juveniles were limited to inshore waters <400 m, most were found between 100 and 200 m. Spring and summer were the preferred seasons for recruitment; although for both seasons there was some interannual variation. Adult distribution also varied, according to the season. Young adults were spread over the entire depth range, with the biggest ones concentrated at the edge of the shelf (150‐350 m), especially in autumn and winter. The main spawning peak coincided with this concentration of adults suggesting that spawning occurred in autumn/winter at the edge of the shelf. ? 1998 The Fisheries Society of the British Isles
TL;DR: The histological analysis of the vertebrae showed that bone compacity and number of trabeculae vary depending on their localization on the vertebral axis, which represents an important source of calcium and other elements during anadromous migration in Atlantic salmon.
Abstract: A quantitative study of morphological and histological changes in the skeleton (cranial bones and vertebrae) of adult Atlantic salmon Salmo salar during its anadromous migration was performed in order to specify various aspects of its skeletal biology in relationship to this migration. At the beginning of the ascent, there was no morphological difference in the cranial bones between males and females. As the spawning season approached, males showed marked secondary sexual characters particularly allometric breeding growth of some bones of the skull. The histological analysis of the vertebral bone tissue along the vertebral axis showed that bone compacity and number of trabeculae vary depending on their localization on the vertebral axis. Moreover, bone compacity decreased significantly with the sexual maturation of the fish whereas the number of trabeculae grew in both sexes. Thus, the vertebrae (like scales) represent an important source of calcium and other elements during anadromous migration in Atlantic salmon.
TL;DR: The combined effects of greater size and rearing experience of hatchery-produced salmon were sufficient to overcome a wild salmon's advantage of prior residence and help to rehabilitate salmonid populations.
Abstract: In aquarium experiments using coho salmon as a model species, prior residents dominated intruders of the same size but intruders with a 6% length advantage were equally matched against prior residents. Prior winning experience (distinct from individual recognition) also strongly influenced competitive success and overcame a prior residence effect. Coho salmon reared in a hatchery dominated size-matched fish from the same parental population reared in a stream. Hatchery-reared salmon also dominated naturally spawned salmon, even when the wild salmon were prior residents. Thus the combined effects of greater size and rearing experience of hatchery-produced salmon were sufficient to overcome a wild salmon's advantage of prior residence. Efforts to rehabilitate salmonid populations must consider such behavioural interactions if displacement of wild fish is to be prevented.
TL;DR: Under free-running conditions, most rainbow trout displayed circadian feeding rhythms, although the expression of circadian rhythmicity depended on the experimental condition; this finding contrasts with the previously recorded lack of an endogenous oscillator in the pineal organ driving the rhythmic secretion of melatonin.
Abstract: Under free-running conditions, most rainbow trout displayed circadian feeding rhythms, although the expression of circadian rhythmicity depended on the experimental condition: 16·7% of fish under constant dim light (LL dim), 66·1% under a 45 :45 min light-dark cycle (LD pulses), and 83·8% under constant light (LL). Under LD pulses, the period length of the free-running rhythms for feeding was significantly shorter (21·9 ± 0·7 h, n=8) than under LL (26·2 ± 0·3 h, n=10). Period length for locomotor activity under LL was 25·8 ± 0·6 h (n=4). Under LD conditions, the daily demand-feeding profile was always confined to the light phase and chiefly composed of two main episodes, directly after lights on (light elicited) and in anticipation to lights off (endogenous). Contrasting to feeding, the diel locomotor activity profile varied remarkably: a diurnal activity pattern at the bottom, while a clearly nocturnal pattern at the surface. These results contribute to a better understanding of feeding and locomotor rhythms of rainbow trout, providing evidence for the existence of a biological clock involved in their circadian control. This finding contrasts with the previously recorded lack of an endogenous oscillator in the pineal organ driving the rhythmic secretion of melatonin, which suggests different locations from the pineal for the circadian pacemakers in this species.
TL;DR: Age and size distributions of subadults and adults at different stages of gametogenesis were sex-specific and conformed with von Bertalanffy growth curves, but this increase was dampened in older females.
Abstract: Three hundred and five Atlantic sturgeon caught in the Hudson River and Hudson Bight were examined for age, body size and gonadal development (histology). Sampled fish ranged in age from 1·5 to 43 years and fork length (LF) 48–244 cm, and included 144 females and 161 males. All young sturgeon (age 1·5–4 years) caught in the river had sexually differentiated gonads. Age and size distributions of subadults and adults at different stages of gametogenesis were sex-specific and conformed with von Bertalanffy growth curves. Males mature faster and at a younger age compared to the females. Females with mid-vitellogenic ovaries were not found and their absence may be related to fishing gear selectivity or out-migration into the ocean during ovarian recrudescence. Mature males and females caught during the spring spawning migration into the Hudson River, ranged in age from 12 to 19 and from 14 to 43 years, and LF 117–185 and 173–244 cm, respectively. Individual fecundity and diameter of fully grown ovarian follicles increased with age and body size, but this increase was dampened in older females. Three hermaphroditic fish were found and all exhibited sparse pre-vitellogenic ovarian follicles embedded in normally developing testicular tissue.
TL;DR: Sperm motility, assessed just after collection in terms of arbitrary motility scores from 0 to 5, was significantly increased both at 10 and 60 s post-activation, for samples collected 18 days after, 25 days before and 9 days after the beginning of the spawning period of the females, respectively.
Abstract: The deleterious effect of the ageing phenomenon of turbot spermatozoa was investigated in relation to the sampling date. Spermatozoa with a low or highly condensed chromatin and a middle piece containing numerous or a few vesicles were observed simultaneously 80 and 47 days before the beginning of the spawning period of the females. The middle piece of spermatozoa contained few vesicles, 39 days after the end of the reproductive period. At the same date, some spermatozoa appeared in which the plasma membrane was broken. Sperm motility, assessed just after collection in terms of arbitrary motility scores from 0 to 5, was significantly increased both at 10 and 60 s post-activation, for samples collected 18 days after, 25 days before and 9 days after the beginning of the spawning period of the females, respectively compared to samples collected 6 days before, 55 days after and 88 days after the end of this period. A lower short-term storage capacity was recorded at 10 and 60 s post-activation for sperm samples collected 6 days before and 88 days after the end of the reproductive period, respectively compared to 18 days and 9 days after the beginning of the spawning period. At 60 s post-activation, a higher motility of thawed spermatozoa was observed for samples collected 5 days before the beginning of the spawning period (motility recovery index: 86.4 ± 19.4%) compared to 71 days after the end of this period (55.0 ± 12.0%). The fertilizing capacity of sperm samples collected 61 days after the end of the spawning season (66.1 ± 14.6%) was significantly lower than that recorded for samples collected 34 days after the beginning of the spawning period (75.2±9.6%). On the contrary, there was no significant decrease in endogenous ATP content (31 days after the beginning of the spawning period, 14.53 ± 0.84; 48 days after the end of this period, 10.75 ± 5.26 nmol 10− 8 spermatozoa). Furthermore, sperm concentration significantly increased between the same dates (respectively 3.3 ± 0.8–9.4±4.8×109 spermatozoa ml−1).
TL;DR: The occurrence of farm genotypes and the independent occurrence of mtDNA and minisatellite markers in several parr samples from the river indicated that escaped juvenile salmon completed their life cycle, bred and interbred with native fish, upon their return to the river.
Abstract: The study was undertaken on three adjacent rivers in NW Ireland, on one of which an Atlantic salmon Salmo salar freshwater juvenile rearing unit is situated. Two markers which distinguished farm and wild populations were used. An Ava II-B RFLP in the ND1 region of mtDNA was at a frequency of 0.58 in the farm strain but absent in the wild populations. Allele E at minisatellite locus Ssa- A45/2/l was at a frequency of 0.91 in farm samples, but at a maximum of 0.41 in the populations in the two rivers adjacent to the one with the juvenile rearing unit. The farm strain showed a significant reduction in mean heterozygosity (0.281 ± 0.057), over three minisatellite loci examined, compared to wild samples (0.532 ± 0.063). The occurrence of farm genotypes and the independent occurrence of mtDNA and minisatellite markers in several parr samples from the river indicated that escaped juvenile salmon completed their life cycle, bred and interbred with native fish, upon their return to the river. Escaped fish homed accurately, as adults, to the site of escape, i.e. the area adjacent to the hatchery outflow in the upstream part of the river. Breeding of males in the lower part of the river was also indicated but this could have been due to mature male parr which had moved downstream. The return of adults of farm origin to the river to breed was indicated by the presence of the Ava II-B haplotype in adults netted in the estuary.
TL;DR: This paper explores the relationship between dissolved oxygen concentration and the distribu- tion and electric signal diversity of 64 species of gymnotiforms from the Teferegion of the upper Amazon basin and finds that tone-type species have less flexible and perhaps greater overall energetic demands that impose handicaps in habitats where oxygen is a limiting factor.
Abstract: This paper explores the relationship between dissolved oxygen concentration and the distribu- tion and electric signal diversity of 64 species of gymnotiforms from the Teferegion of the upper Amazon basin. Seventeen species are able to tolerate protracted periods of anoxia in inundated varzea floodplains or in terra firme swamps. The majority do so by breathing air—either with specialist accessory air-breathing organs or via their gills. An assemblage of 38 species of gymnotiforms which are unable to tolerate hypoxia undertake lateral migrations from well-oxygenated river channels into and out of the varzea floodplain in response to oxygen availability. These have evolved behavioural adaptations to avoid hypoxic water. While there is a mix of tone- and pulse-type electric organ discharges (EODs) in species that live only in permanently well-oxygenated habitats, 16 out of the 17 species that live in anoxic habitats have pulse-type EODs. The tone-type signals may have less flexible and perhaps greater overall energetic demands that impose handicaps in habitats where oxygen is a limiting factor. Many tone-type species also have more active swimming behaviour which could impose further energetic demands. ? 1998 The Fisheries Society of the British Isles
TL;DR: The sensory basis of Chinese perch in feeding is well adapted to its nocturnal stalking hunting strategy, and also explains its peculiar food habit of accepting live prey fish only and refusing dead prey fish or artificial diets.
Abstract: Experiments were conducted to identify the roles of the individual sense organs in the feeding behaviour of Chinese perch Siniperca chuatsi by determining the consumption of natural food after selective removal or blocking of eyes, lateral lines and olfactory organs, and also by observing the behavioural response to visual, mechanical and chemical stimulation by artificial prey. Chinese perch were able to feed properly on live prey fish when either eyes or lateral lines were intact or functional, but could scarcely feed without these two senses. Chinese perch recognized its prey by vision through the perception of motion and shape, and showed a greater dependence on vision in predation when both visual and mechanical cues were available. Chemical stimulation by natural food could not elicit any feeding response in Chinese perch, and gustation was only important to the fish for the last stage of food discrimination in the oropharyngeal cavity. The sensory basis of Chinese perch in feeding is well adapted to its nocturnal stalking hunting strategy, and also explains its peculiar food habit of accepting live prey fish only and refusing dead prey fish or artificial diets.
TL;DR: A significant portion of the benthic habitats in the Gulf are uninhabitable for cod which would be expected to avoid waters below 28% oxygen saturation, which is a permanent feature of the deep waters of the Gulf of St Lawrence.
Abstract: Oxygen saturation levels that killed 50 and 5% of cod Gadus morhua over 96 h averaged 21·2 and 27·7%, respectively. No fish survived at 10% saturation and only a few survived at 16% saturation, whereas no mortality occurred at 34 and 40% oxygen saturation. Since metabolic rate and oxygen consumption increase with increasing temperature, we hypothesized that cod would be less tolerant to hypoxic conditions at 6 than at 2° C. However, temperature (2 and 6° C) had no measurable impact on cod survival. Small (mean & S.D.; 45·2 ± 4·2 cm) and large (57·5 ± 3·8 cm) cod had the same tolerance to hypoxia. At the end of the experiments, hypoxia had a significant effect on blood haematocrit, mean cellular haemoglobin content, liver lactate, plasma glucose and plasma lactate, but accounted for only a small fraction (< 10%) of the variation, except for plasma lactate which exhibited a strong response with concentrations increasing progressively with decreasing levels of oxygen saturation. Temperature had a significant effect on most variates in normoxia and hypoxia. Variates also affected by oxygen level showed significant interactions between oxygen and size or temperature effects. However, these interactions accounted for only a small proportion of the variation. Physiological parameters indicated that extending the duration of our tests beyond 96 h would not have changed our estimates of the lethal thresholds. Hypoxic conditions are a permanent feature of the deep waters of the Gulf of St Lawrence. This study shows that a significant portion of the benthic habitats in the Gulf are uninhabitable for cod which would be expected to avoid waters below 28% oxygen saturation.
TL;DR: The results of this study suggest that the metabolic response of juvenile salmonids to changes in salinity is dependent on life-history stage (e.g. fry v. smolt), and that oxygen consumption rates do not necessarily reflect osmoregulatory costs.
Abstract: The metabolic response of juvenile coho salmon Oncorhynchus kisutch to different salinities was examined, using whole-animal oxygen consumption rates and gill Na+, K+-ATPase activities as indicators of osmoregulatory energetics. Coho salmon smolts were acclimated to fresh water (FW), isosmotic salinity (ISO, 10‰) and sea water (SW, 28‰) and were sampled for up to 6 weeks for plasma levels of cortisol, glucose and ions (Na+, K+, Cl−), gill Na+, K+-ATPase activity and oxygen consumption rates. Following an initial adjustment period, plasma constituents in SW fish returned to near-FW values, indicating that the fish were acclimated to SW by day 21. Gill Na+, K+-ATPase activities on days 21 and 42 were lowest in ISO, higher in FW and highest in SW. This result is consistent with the idea that less energy would be required to maintain ion balance in an isosmotic environment, where the ionic gradients between extracellular fluid and water would be minimal. Oxygen consumption rates of swimming fish (1 body length s−1), however, did not differ significantly between the three test salinities after 6 weeks. The results of this study suggest that the metabolic response of juvenile salmonids to changes in salinity is dependent on life-history stage (e.g. fry v. smolt), and that oxygen consumption rates do not necessarily reflect osmoregulatory costs.
TL;DR: The efficiency of utilizing yolk energy for growth was high as compared with other fish species (57% during the whole endogenous feeding period); it was temperature independent; however, time was used less efficiently at low temperatures, increasing a risk of predation.
Abstract: Fertilized Chondrostoma nasus eggs were incubated at 10, 13, 16 and 19° C until full resorption of the yolk sac. High survival was observed at 10–16° C (89–92% at the onset of external feeding), whereas at 19) C survival was depressed (76%). The time at which 5, 50 and 95% of individuals had hatched, filled the swim bladder, ingested the first food and fully resorbed the yolk sac was determined. An increase in temperature accelerated development and made it more synchronous. Within the period from fertilization to hatching embryonic development was theoretically arrested (t0 dev) at 8·8° C, and growth was arrested (t0gr) at 8·86° C. For the whole endogenous feeding period (from fertilization to full yolk resorption) the amount of matter transformed into tissue was temperature independent between 10° and 19° C. Respiration increased exponentially with age; the respiration increase was faster at higher temperatures, but, in general, metabolic expenditures of C. nasus were low. As a consequence, the efficiency of utilizing yolk energy for growth was high as compared with other fish species (57% during the whole endogenous feeding period); it was temperature independent. However, time was used less efficiently at low temperatures, increasing a risk of predation. Within the endogenous feeding period a shift from lower to higher temperatures for optimal yolk utilization efficiency was observed. The temperatures optimal for survival and energetic performance seem to be 13–16° C for egg incubation and 15–18° C for rearing of yolk-feeding larvae. Chondrostoma nasus is a potential candidate for aquaculture for restocking purposes.
TL;DR: Serum levels of 17β-oestradiol and testosterone peaked and fell within 6 days of spawning in Tilapia zillii suggesting that vitellogenic growth began as early as day 2 or 3 postspawning, and previteLLogenic oocytes are recruited into vitelliogenic growth immediately after spawning.
Abstract: Serum levels of 17β-oestradiol and testosterone peaked and fell within 6 days of spawning in Tilapia zillii suggesting that vitellogenic growth began as early as day 2 or 3 postspawning As early as day 8, stage 6/7 (late nitellogenic and maturing) oocytes occupied 60–70% of the ovary From day 8 onwards the proportion of stage 6/7 oocytes changed little, though IG increased (as oocytes grew) to reach maximal levels of ∼ 5·5% by day 14 IG was correlated significantly to the proportion of stage 6/7 oocytes Postovulatory follicles were observed immediately following spawning occupying up to ∼ 7% of the ovary but were not present from day 3 onwards Atretic oocytes were found throughout the time period monitored (generally occupying <2% of the ovary) but were more prevalent from day 18 onwards Data suggest that previtellogenic oocytes are recruited into vitellogenic growth immediately after spawning and can complete vitellogenesis as early as day 8 postspawning Knowledge of this timing is likely to be important in the development of spawning induction programmes in T zillii and other related species
TL;DR: The results suggest that fish from distinct populations can diVer in the degree of diet selectivity according to their energetic requirements for growth, and the fast learning response of Atlantic salmon parr towards novel prey probably allows fish to maintain a high foraging eYciency when faced with frequent changes in the availability of diVerent prey types.
Abstract: Both in foraging groups and in a sequential prey encounter context, learning had a visible eVect on the pattern of selection for three live prey types (Ecdyonurus larvae, Hydropsyche larvae, and Gammarus) by juvenile Atlantic salmon Salmo salar. Compared to wild-caught fish, naive, hatchery-reared fish that had not been exposed to natural prey ate Hydropsyche larvae in a remarkably low proportion, and consumed a higher proportion of Gammarus. Ecdyonurus experienced a high and rather steady predation rate across the experience gradient, but after a short period of experience with live prey the consumption rate for Hydropsyche increased drastically, and that of Gammarus decreased, matching the selection pattern exhibited by wild fish. Individual fish oVered prey in a sequential encounter context increased consumption rates of all the prey types as they gained experience, but the improvement was higher for the prey that were less consumed initially. Fish became more selective as they approached satiation, conforming to the prediction of optimal foraging theory that higher predator’s energy requirements, as well as low food availability, result in reduced selectivity. The results also suggest that fish from distinct populations can diVer in the degree of diet selectivity according to their energetic requirements for growth. The fast learning response of Atlantic salmon parr towards novel prey probably allows fish to maintain a high foraging eYciency when faced with frequent changes in the availability of diVerent prey types. ? 1998 The Fisheries Society of the British Isles