Individual Fish (individual + fish)

Distribution by Scientific Domains

Terms modified by Individual Fish

  • individual fish weight

  • Selected Abstracts


    Linking habitat selection, emigration and population dynamics of freshwater fishes: a synthesis of ideas and approaches

    ECOLOGY OF FRESHWATER FISH, Issue 2 2006
    T. E. McMahon
    Abstract,,, The consequences of individual behaviour to dynamics of populations has been a critical question in fish ecology, but linking the two has proven difficult. A modification of Sale's habitat selection model provides a conceptual linkage for relating resource availability and individual habitat selection to exploratory behaviour, emigration and population-level responses. Whole-population experiments with pupfish Cyprinodon macularius that linked all factors along this resource to population continuum lend support to this conceptual model, and illustrate that emigration may be much more common in fish populations than considered in most individual- or population-based models. Accommodating emigration can enhance the ecological appropriateness of behavioural experiments and increase confidence in extrapolation of experimental observations to population-level effects. New experimental designs and advancing technologies offer avenues for assessing population consequences of habitat selection and emigration by individual fish. Emigration often is the key linkage between individual behaviour and population responses, and greater understanding of the underlying factors affecting this often-overlooked demographic parameter could offer new approaches for management and conservation of fishes. [source]


    The effects of kin and familiarity on interactions between fish

    FISH AND FISHERIES, Issue 4 2003
    Ashley J W Ward
    Abstract Fish have been shown to discriminate between individuals on very general bases such as species, body length and colour. More recently, evidence has been accumulating from a number of species that relatedness and familiarity may be extremely important in mediating a range of interactions between individual fish. Studies have shown that fish are able to recognize kin and/or familiars, and that this ability potentially conveys significant benefits, including increased inclusive fitness, reduced inbreeding costs, reduced competition and enhanced antipredator behaviour. Here, we review the literature and consider future directions and applications for this research. [source]


    Run timing and migration routes of returning Atlantic salmon in the Northern Baltic Sea: implications for fisheries management

    FISHERIES MANAGEMENT & ECOLOGY, Issue 3 2009
    A. SIIRA
    Abstract, Return migration of Atlantic salmon, Salmo salar L., was studied in the Gulf of Bothnia, northern Baltic Sea, by a mark-recapture experiment and catch records from commercial trap-nets. Coastal salmon fishing is regulated by delayed opening of the fishery in consecutive regions based on the assumption that the wild fish migrate before reared ones and the migration is unidirectional and continuous from south to north. Neural network modelling suggested that the migration does not progress linearly from one regulation region to another, but shows variation between origin and sea age among and within regions. Further evidence of the non-linear migration included a noticeable part of salmon on their way to two major estuaries first visiting the northern-most Bothnian Bay before turning back south. Salmon returning to the different homing sites in the north showed no differences in run timing in the southern Gulf whereas the same individual fish showed differences in catch accumulation further north. Run timing estimates indicated only a slight tendency towards earlier migration for wild salmon compared with reared fish. [source]


    Use of tag data to compare growth rates of Atlantic coast striped bass stocks

    FISHERIES MANAGEMENT & ECOLOGY, Issue 5 2003
    S. A. Welsh
    Abstract Migratory stocks of Atlantic coast striped bass, Morone saxatilis (Walbaum), range primarily from North Carolina (NC) northward to Canadian waters. Between 1986 and 2000, 267 045 wild striped bass were tagged and released from NC to Massachusetts as part of the Cooperative Striped Bass Tagging Program. Direct measurements of growth of individual fish can be obtained from tag data and are useful for understanding the dynamics of fish populations. Growth rates from regressions of length-increment vs. time-at-liberty were estimated for striped bass tagged and released in three southern states [NC, Virginia (VA) and Maryland (MD)] and three northern states (New Jersey, New York and Rhode Island). Striped bass tagged in waters of northern states grew faster (significantly steeper regression slopes) than those tagged in southern areas. Migratory patterns, stock mixing, and unmeasured biotic and abiotic influences on growth precluded conclusions that observed growth patterns are stock-specific. These results, however, indicate latitudinal differences in growth rates, and should be considered in future research and management of Atlantic coast striped bass. [source]


    The influence of pelagic habitat selection and interspecific competition on productivity of juvenile walleye pollock (Theragra chalcogramma) and capelin (Mallotus villosus) in the Gulf of Alaska

    FISHERIES OCEANOGRAPHY, Issue 4 2010
    ELIZABETH A. LOGERWELL
    Abstract Here we investigate processes affecting productivity of capelin and walleye pollock in the Gulf of Alaska. We examine pelagic habitat selection by comparing the distribution of juvenile fish and their prey with oceanographic properties and we evaluate the potential for interspecific competition by comparing diets and measures of foraging. The primary field study was conducted in Barnabus Trough, Kodiak Island, Alaska, during September 2005. The distribution of fish was assessed acoustically and trawls were used to collect individual fish for stomach content analyses. Physical and biological data were collected with conductivity,temperature,depth probes and zooplankton tows. Age-0 pollock were distributed in cool waters offshore of a mid-trough front, coincident with the distribution of euphausiids, their preferred prey. In contrast, capelin and their prey (copepods) were distributed throughout the trough. We observed that sympatric capelin (occurring with pollock) often had reduced foraging success compared to allopatric capelin (occurring alone). Results of a bioenergetic model also suggest that the exclusion of capelin from foraging on euphausiids can have negative consequences for capelin growth. [source]


    Trading safety for food: evidence from gut contents in roach and bleak captured at different distances offshore from their daytime littoral refuge

    FRESHWATER BIOLOGY, Issue 5 2006
    Z. MACIEJ GLIWICZ
    Summary 1. Regular diel habitat shifts in roach were detected by hydro-acoustics in five moderately eutrophic, stratifying (maximum depth 24,27 m) and approximately circular lakes (of surface area 15, 75, 125, 300 and 900 ha and diameters 250, 600, 1000, 1700 and 2600 m) in north-eastern Poland in the years 1998,2000, when the lakes were free of smelt and other typical offshore planktivores, and their offshore areas were completely free of fish during the day. 2. The diel change in roach distribution was shown to assume a similar pattern in each lake: fish migrated from a daytime littoral refuge towards the centre of the lake at dusk, and returned to the littoral refuge at dawn. After sunset, fish gradually dispersed offshore until they covered the entire lake area in each of the three smaller lakes. In each of the two larger lakes, only small numbers of fish were seen in the central area at night, implying that the centre of the lake retained high food availability throughout the summer. 3. Inshore,offshore gradients in zooplankton prey density, body size, and numbers of eggs per clutch were weak or undetectable in the two smallest lakes, but strong and persistent in the three larger lakes, with Daphnia densities 5,30 times as high and body length 1.2,1.5 times as great in the central area as inshore. 4. The likely increase in the potential predation risk with distance from the littoral daytime refuge was found to be compensated by increased food gains in those fish which moved offshore at dusk to feed within a short time window, when light intensity was lower to make the risk reduced, but still high enough to see zooplankton prey. The benefit because of increased prey acquisition was greatest in the centre of the largest lake (at 1300 m from the shore), as revealed from gut inspections of roach and bleak trawl-sampled at different distances from the edge of the reed belt, and seen as a gradual, order-of-magnitude increase in the volume of food in the foregut, The food volume against distance-from-shore regression was highly significant on each of the four sampling dates in the largest lake, in spite of the wide variability of food volume in individual fish. [source]


    Testing the assumptions of the ideal despotic distribution with an unpredictable food supply: experiments in juvenile salmon

    JOURNAL OF ANIMAL ECOLOGY, Issue 2 2005
    AMANDA MACLEAN
    Summary 1Models linking the behaviours of individual animals, their positions within socially complex groups and spatio-temporal variation in resource distribution offer a promising base for predicting population responses to changing environments. The ideal free and despotic distributions and their derivatives are particularly influential in this regard. 2Due to the difficulties of conducting work in the wild, for some groups of animals such models are often based on observations of animals in small-scale systems under conditions that are well controlled, but unnaturally simple. 3Using an experimental system based on field observations of home range size and variation in food availability, the present study tested whether models derived using small-scale laboratory observations are valid for juvenile Atlantic salmon in more natural conditions. 4Contrary to predictions, we found no differences in behaviour between the control fish (which experienced consistently rich feeding patches) and the experimental fish (which experienced unpredictable 10-fold changes in patch quality). 5Also contrary to predictions, in the variable condition, salmon used high quality patches (which were an order of magnitude better than low quality patches) only marginally (5%) more than would be expected if they were to forage at random. There was significant variation in foraging strategies between individual fish, with 28% of the population making non-random use of foraging patches. 6The only apparent systematic relationship between social rank and use of foraging patches was that fish that were both dominant and made many moves between feeding locations tended to leave rich patches less frequently than they left poor patches. 7Despite the low correlation between patch quality and movement, there was substantial movement of fish among patches. Forty-four per cent of moves followed aggressive interactions and most others were spontaneous, with no obvious motivating factor apparent. 8The study exposes a discrepancy between expectations derived from the basic concepts of patch choice theory and the behaviour of Atlantic salmon in the conditions pertaining in the present study. 9It is suggested that this discrepancy may arise both from the fact that applicability of patch choice models may be very sensitive to the stability of differences in patch quality and from uncertainties about the costs of habitat sampling. [source]


    Seasonal growth patterns of wild juvenile fish: partitioning variation among explanatory variables, based on individual growth trajectories of Atlantic salmon (Salmo salar) parr

    JOURNAL OF ANIMAL ECOLOGY, Issue 1 2005
    P. J. BACON
    Summary 1We present an empirical, analytical model that estimates both temperature and seasonal response functions for the growth of wild juvenile fish without the need for costly tank experiments in less realistic conditions. 2Analysis of monthly recapture data on the lengths and weights of individual wild juvenile fish demonstrates that simple temperature-driven models of growth can be less informative than more realistic, empirical, models. 3A case study of wild Atlantic salmon parr (Salmo salar) showed that: most growth took place in a 10-week period in spring, at temperatures below those that previous published models report as necessary for rapid growth and at faster rates than the maximum that previous models predicted. 4Temperature and fish size allometry explained 45% of growth variation, but the effects of temperature were significantly and markedly different at different seasons. 5Seasonal effects explained an additional 18% of the variation and were strongly associated with the abundance of potential ,drift' food. 6The seasonal patterns for growth in length and weight were different, implying differential allocation of resources to structural and reserve tissues. 7The growth patterns of sexually maturing male parr and emigrants also differed in comparison to other parr. 8Condition factor, length at first capture and seasonal interactions with both early maturity and smolting explained another 7% of the variation. 9However, individual fish did not grow consistently better, or worse, than the ,average' fish. 10This study emphasizes the necessity to test the adequacy of laboratory-based physiological models with suitably detailed field data and to focus model refinement by identifying processes which otherwise confound interpretation. [source]


    Restricted fish feeding reduces cod otolith opacity

    JOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2008
    H. Hřie
    Summary The purpose of this work was to examine the effect of reduced feeding and constant temperature on cod otolith opacity. Three groups of juvenile cod were given restricted food rations at different times for 4 months, resulting in depressed somatic growth. Otolith opacity was measured on pictures of the otolith sections. The otolith carbonate deposited during the experimental period was generally opaque compared to the more translucent otolith material deposited prior to and after the experimental period, when the fish were kept in a pond and in sea-cages at higher temperatures. Large variations in otolith opacity were found between individual fish both within groups and between groups. In two of the three groups significantly more translucent otolith material was deposited in response to reduced feeding. Our results show that variations in feeding and hence fish growth resulted in variation in otolith opacity, but the effect was minor compared to that of variations in ambient temperature. The combined influence of these effects, which both act on fish metabolism, are most likely controlling the seasonal opacity changes observed in wild fish. Our results help explain the variations seen in fish at constant temperatures. [source]


    Estimation of gonad volume, fecundity, and reproductive stage of shovelnose sturgeon using sonography and endoscopy with application to the endangered pallid sturgeon

    JOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2007
    By J. L. Bryan
    Summary Most species of sturgeon are declining in the Mississippi River Basin of North America including pallid (Scaphirhynchus albus F. and R.) and shovelnose sturgeons (S. platorynchus R.). Understanding the reproductive cycle of sturgeon in the Mississippi River Basin is important in evaluating the status and viability of sturgeon populations. We used non-invasive, non-lethal methods for examining internal reproductive organs of shovelnose and pallid sturgeon. We used an ultrasound to measure egg diameter, fecundity, and gonad volume; endoscope was used to visually examine the gonad. We found the ultrasound to accurately measure the gonad volume, but it underestimated egg diameter by 52%. After correcting for the measurement error, the ultrasound accurately measured the gonad volume but it was higher than the true gonad volume for stages I and II. The ultrasound underestimated the fecundity of shovelnose sturgeon by 5%. The ultrasound fecundity was lower than the true fecundity for stage III and during August. Using the endoscope, we viewed seven different egg color categories. Using a model selection procedure, the presence of four egg categories correctly predicted the reproductive stage ± one reproductive stage of shovelnose sturgeon 95% of the time. For pallid sturgeon, the ultrasound overestimated the density of eggs by 49% and the endoscope was able to view eggs in 50% of the pallid sturgeon. Individually, the ultrasound and endoscope can be used to assess certain reproductive characteristics in sturgeon. The use of both methods at the same time can be complementary depending on the parameter measured. These methods can be used to track gonad characteristics, including measuring Gonadosomatic Index in individuals and/or populations through time, which can be very useful when associating gonad characteristics with environmental spawning triggers or with repeated examinations of individual fish throughout the reproductive cycle. [source]


    Coping strategies in farmed African catfish Clarias gariepinus.

    JOURNAL OF FISH BIOLOGY, Issue 10 2010
    Does it affect their welfare?
    The objective of this study was to assess whether and how coping strategies affect the welfare of African catfish Clarias gariepinus housed at low and high densities. Group composition influenced feed intake; re-active groups (comprised of 100% re-active fish) had a lower specific growth rate (G) and feed intake and a higher feed conversion ratio (RFC) than pro-active groups. Furthermore, re-active groups had a lower energy retention than pro-active groups. The latter was fully due to differences in feed intake, since energy partitioning (on % total gross energy intake basis) was similar among the group composition treatments. Fish held at high stocking density showed a higher RFC and feeding speed and a lower energy retention and agonistic behaviour. None of the measured variables was influenced by the interaction effect. In mixed groups, G and number of skin lesions seemed to be affected by different behavioural phenotypes at low stocking density, but not at high density. These results indicate that both stocking density and group composition affect physical and behavioural responses of C. gariepinus. Furthermore, physical and behavioural data of individual fish housed in mixed groups suggest that coping strategy affects the fitness of different behavioural phenotypes at low, but not at high, stocking density. [source]


    Effect of Ligula intestinalis on the reproductive capacity of Rastrineobola argentea in Lake Victoria

    JOURNAL OF FISH BIOLOGY, Issue 9 2008
    I. G. Cowx
    This study examined the potential effect of the cestode Ligula intestinalis on the reproduction of the indigenous cyprinid Rastrineobola argentea in Lake Victoria. Ligula intestinalis had a marked effect on the breeding cycle of R. argentea. The proportion of the infected population in advanced stages of maturation prior to spawning was considerably reduced compared with uninfected fish. Infection by L. intestinalis significantly reduced the fecundity of individual fish, particularly in the 45,60 mm size range; the component of the population that makes the greatest contribution to reproductive output. The reduction in reproductive output of the R. argentea population could potentially affect replenishment of stocks in this important fishery. [source]


    Identifying individual great barracuda Sphyraena barracuda using natural body marks

    JOURNAL OF FISH BIOLOGY, Issue 3 2006
    S. K. Wilson
    Natural body marks on Sphyraena barracuda were recorded with digital images to identify individual fish. Over 18 months, 60 fish were photographed in situ, eight of which were re-photographed at later dates. Re-photographed fish were all large adults (>70 cm total length) and were all seen within 200 m of the site where they were originally observed 10,318 days prior. Over the same period and area, 116 fish were tagged using T-bar tags, yet none of these fish were recaptured. Natural body marks are thus an effective means of identifying and monitoring behaviour of individuals. [source]


    Morphometry and composition of aragonite and vaterite otoliths of deformed laboratory reared juvenile herring from two populations

    JOURNAL OF FISH BIOLOGY, Issue 6 2003
    J. Tomás
    Vaterite otoliths were sampled from two reared populations (Celtic and Clyde Seas) of juvenile herring Clupea harengus. The crystallography, elemental composition and morphometry were analysed and compared with those of normal aragonite otoliths. The incidence of vaterite otoliths in the juveniles sampled (n = 601) ranged from 7·8% in the Clyde population to 13·9% in the Celtic Sea population, and was 5·5% in the small sample (n = 36) of wild adults examined. In all but one case fish had only one vaterite otolith; the corresponding otolith of the pair was completely aragonite. Although the majority of the juveniles sampled showed craniofacial deformities, there was no link between the skull or jaw malformation and the incidence of vaterite otoliths. All vaterite otoliths had an aragonite inner area, and vaterite deposition began sometime after the age of 90 days. The vaterite otoliths were larger and lighter than their corresponding aragonite partners, and were less dense as a consequence of the vaterite crystal structure. The vaterite areas of the otoliths were depleted in Sr, Na and K. Concentrations of Mn were higher in the vaterite areas. The transition between the aragonite inner areas and the vaterite areas was sharply delineated. Within a small spatial scale (20 ,m3) in the vaterite areas, however, there was co-precipitation of both vaterite and aragonite. The composition of the aragonite cores in the vaterite otoliths was the same as in the cores of the normal aragonite otoliths indicating that the composition of the aragonite cores did not seed the shift to vaterite. Vaterite is less dense than aragonite, yet the concentrations of Ca analysed with wavelength-dispersive spectrometry (WDS) were the same between the two polymorphs, indicating that Ca concentrations measured with WDS are not a good indicator of hypermineralized zones with high mineral density. The asymmetry in density and size of the otoliths may cause disruptions of hearing and pressure sensitivity for individual fish with one vaterite otolith, however, the presence of vaterite otoliths did not seem to affect the growth of these laboratory reared juvenile herring. [source]


    Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmon

    JOURNAL OF FISH BIOLOGY, Issue 4 2003
    D. R. Geist
    Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O2 h,1 at 30 cm s,1 (c. 0·5 BL s,1) to 3347 mg O2 h,1 at 170 cm s,1 (c. 2·3 BL s,1). Corrected for fish mass, these values ranged from 122 to 670 mg O2 kg,1 h,1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s,1, and a third-order polynomial regression model fitted the data best. The upper critical swim speed (Ucrit) of fish tested at two laboratories averaged 155 cm s,1 (2·1 BL s,1), but Ucrit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s,1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s,1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s,1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the Ucrit for the fish used in the EMG trials (mean Ucrit 168·2 cm s,1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ,80% of the Ucrit. [source]


    Oxygen and salinity characteristics of predator,prey distributional overlaps shown by predatory Baltic cod during spawning

    JOURNAL OF FISH BIOLOGY, Issue 1 2003
    S. Neuenfeldt
    In the distributional overlap volume of Baltic cod Gadus morhua and its prey, studied in the Bornholm Basin in the southern Baltic Sea, only a fraction of the sprat Sprattus sprattus population vertically overlapped with the Baltic cod population. Sprat occurred in the intermediate water, in the halocline and in the bottom water, while herring Clupea harengus and Baltic cod occurred exclusively in the halocline and in the bottom water. Only parts of the sprat population were hence accessible for Baltic cod, and only a fraction of the sprat had access to the Baltic cod eggs below the halocline. Baltic cod,clupeid overlap volumes appeared to be determined by salinity stratification and oxygenation of the bottom water. Hydrography time series were used to estimate average habitat volumes and overlap from July to September in 1958,1999. In the 1999 survey spawning Baltic cod had greater ratios of empty stomachs and lower average rations than non-spawning Baltic cod. The average ration for Baltic cod caught within 11·,4 m from the bottom (demersal) did not differ from the average ration of Baltic cod caught in shallower waters (pelagic), because spawning and non-spawning Baltic cod in both strata were caught at equal rates. The diet of the Baltic cod caught demersally contained more benthic invertebrates, especially Saduria entomon, but Baltic cod caught pelagically also had fresh benthic food in their stomachs, indicating vertical migration of individual fish. [source]


    Genetic analysis of aquabirnaviruses isolated from wild fish reveals occurrence of natural reassortment of infectious pancreatic necrosis virus

    JOURNAL OF FISH DISEASES, Issue 7 2009
    I Romero-Brey
    Abstract In this study, we report the sequencing of the whole genome [including the 5, and 3, non-coding regions (NCR) of both segments A and B] of seven birnavirus strains isolated from wild fish from the Flemish Cap (FC) fishery at Newfoundland, Canada. From analysis and comparison of the sequences, most of the FC isolates clustered with the North American reference strains West Buxton (WB), Dry Mill and Jasper. One strain was included in the same genotype as the European strain Ab. In addition, at least in one case cohabitation of both type strains in an individual fish was demonstrated. These results clearly suggest the acquisition of the viruses from two different sources. The prevalence of the American type is easily explained by the close proximity of this fishing bank to the American coast whereas, although surprising, the presence of the European type strain could be because of migration of fish from European waters. In one strain, segment A and B sequences were typed differently (WB and Ab, respectively). These findings indicate natural reassortment between two strains of aquabirnaviruses in a host. [source]


    Systemic and mucosal antibody response in tilapia, Oreochromis niloticus (L.), following immunization with Flavobacterium columnare

    JOURNAL OF FISH DISEASES, Issue 10 2004
    L D Grabowski
    Abstract Specific antibody responses to Flavobacterium columnare (isolate ATCC 23463T) were characterized in plasma and mucus of tilapia following intraperitoneal (i.p.) injection or immersion immunization with formalin-killed sonicated or whole cell preparations. Fish (30 per treatment) received a primary immunization and were booster immunized 4 weeks later. An enzyme-linked immunosorbent assay was developed for detection and quantification of specific anti- F. columnare antibody, and it was found that formalin-killed sonicated cells in Freund's complete adjuvant (FCA) injected i.p. stimulated a significant systemic antibody response within 2 weeks (mean titre 11 200) which increased to 30 600 following secondary immunization. At 10 weeks post-immunization, the mean titre remained significantly elevated above the controls. Antibodies were also observed in cutaneous mucus of fish immunized i.p. with formalin-killed sonicated cells in FCA at 6 and 8 weeks post-immunization (mean titres 67 and 33, respectively). Although some individual fish responded, mean plasma and cutaneous mucus antibody titres were not significantly greater than controls in any of the other treatment groups. The results of this study demonstrate that tilapia can mount a significant humoral response in plasma and cutaneous mucus to F. columnare, but i.p. immunization with FCA is required to elicit this response. [source]


    The relationship between flesh quality and numbers of Kudoa thyrsites plasmodia and spores in farmed Atlantic salmon, Salmo salar L.

    JOURNAL OF FISH DISEASES, Issue 8 2003
    J A Dawson-Coates
    Abstract Atlantic salmon, Salmo salar L., were exposed to Kudoa thyrsites (Myxozoa, Myxosporea)-containing sea water for 15 months, and then harvested and assessed for parasite burden and fillet quality. At harvest, parasites were enumerated in muscle samples from a variety of somatic and opercular sites, and mean counts were determined for each fish. After 6 days storage at 4 °C, fillet quality was determined by visual assessment and by analysis of muscle firmness using a texture analyzer. Fillet quality could best be predicted by determining mean parasite numbers and spore counts in all eight tissue samples (somatic and opercular) or in four fillet samples, as the counts from opercular samples alone showed greater variability and thus decreased reliability. The variability in both plasmodia and spore numbers between tissue samples taken from an individual fish indicated that the parasites were not uniformly distributed in the somatic musculature. Therefore, to best predict the probable level of fillet degradation caused by K. thyrsites infections, multiple samples must be taken from each fish. If this is performed, a mean plasmodia count of 0.3 mm,2 or a mean spore count of 4.0 × 105 g,1 of tissue are the levels where the probability of severe myoliquefaction becomes a significant risk. [source]


    Effect of Light Intensity on Color Performance of False Clownfish, Amphiprion ocellaris Cuvier

    JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 3 2009
    Inayah Yasir
    Color performance of false clownfish, Amphiprion ocellaris Cuvier, was examined under three levels of light intensity (20,50 , 600,850 , and 2700,3500 lx) for 5 wk. The experiment was conducted in nine rectangular glass aquaria (25 × 25 × 20 cm) with three replicates. Each aquarium was stocked with 36 fish, and 3 fish were randomly sampled from each aquarium every other week. Digital images were taken weekly on each individual fish after it was anesthetized in MS-222. The color performance in hue, saturation, and brightness was quantified using image analysis. In addition to the whole-body analysis, each fish image was divided into ventral and dorsal parts to assess the body position-dependent effect. Furthermore, color differences between dorsal fin, anal fin, ventral fin, and caudal fin were also quantified. The whole body was brighter at low light than at medium or at high light intensity. Irrespective of light intensity, the dorsal side was more orange but less bright than the ventral side. Brighter light strengthened overall orange color on fish fins. The dorsal fin and ventral fins appeared more orange than the anal and caudal fins regardless of light intensity and exposure duration. Similar to body color, low light also led to brighter fins, especially for caudal and dorsal fins. Our results indicate that ambient light could regulate fish color performance but could not change the pigment dominance by ,-carotene. Light intensity is unlikely to change the contrast between dorsal and ventral sides, but dim light tends to make fish body brighter, and bright light strengthens orange color on fins. [source]


    Effect of Dietary Protein Concentration and Stocking Density on Production Characteristics of Pond-Raised Channel Catfish Ictalurus punctatus

    JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 2 2003
    Menghe H. Li
    Diets containing 28% and 32% crude protein were compared for pond-raised channel catfish Ictalurus punctatus stocked at densities of 14,820, 29,640, or 44,460 fish/ha. Fingerling channel catfish with average initial weight of 48.5 g/fish were stocked into 30 0.04-ha ponds. Five ponds were randomly allotted for each dietary protein ± stocking density combination. Fish were fed once daily to satiation for two growing seasons. There were no interactions between dietary protein concentration and stocking density for any variables. Dietary protein concentrations (28% or 32%) did not affect net production, feed consumption and weight gain per fish, feed conversion ratio, survival, processing yields, fillet moisture, protein and ash concentrations, or pond water ammonia and nitrite concentrations. Fish fed the 32% protein diet had slightly but significantly lower levels of visceral and fillet fat than fish fed the 28% protein diet. As stocking density increased, net production increased, while weight gain of individual fish, feed efficiency, and survival decreased. Stocking densities did not affect processing yield and fillet composition of the fish. Although highly variable among different ponds and weekly measurements, ponds stocked at the highest density exhibited higher average levels of total ammonia-nitrogen (TAN) and nitrite-nitrogen (NO2 -N) than ponds stocked at lower densities. However, stocking density had no significant effect on un-ionized ammonia-nitrogen (NH3 -N) concentrations, calculated based on water temperature, pH, and TAN. By comparing to the reported critical concentration, a threshold below which is considered not harmful to the fish, these potentially toxic nitrogenous compounds in the pond water were generally in the range acceptable for channel catfish. It appears that a 28% protein diet can provide equivalent net production, feed efficiency, and processing yields as a 32% protein diet for channel catfish raised in ponds from advanced fingerlings to marketable size at densities varying from 14,820 to 44,460 fish/ha under single-batch cropping systems. Optimum dietary protein concentration for pond-raised channel catfish does not appear to be affected by stocking density. [source]


    Strong population structure despite evidence of recent migration in a selfing hermaphroditic vertebrate, the mangrove killifish (Kryptolebias marmoratus)

    MOLECULAR ECOLOGY, Issue 13 2007
    ANDREY TATARENKOV
    Abstract We employ a battery of 33 polymorphic microsatellite loci to describe geographical population structure of the mangrove killifish (Kryptolebias marmoratus), the only vertebrate species known to have a mixed-mating system of selfing and outcrossing. Significant population genetic structure was detected at spatial scales ranging from tens to hundreds of kilometres in Florida, Belize, and the Bahamas. The wealth of genotypic information, coupled with the highly inbred nature of most killifish lineages due to predominant selfing, also permitted treatments of individual fish as units of analysis. Genetic clustering algorithms, neighbour-joining trees, factorial correspondence, and related methods all earmarked particular killifish specimens as products of recent outcross events that could often be provisionally linked to specific migration events. Although mutation is the ultimate source of genetic diversity in K. marmoratus, our data indicate that interlocality dispersal and outcross-mediated genetic recombination (and probably genetic drift also) play key proximate roles in the local ,clonal' dynamics of this species. [source]


    Karyotype analysis of the yellowtail kingfish Seriola lalandi lalandi (Perciformes: Carangidae) from South Australia

    AQUACULTURE RESEARCH, Issue 15 2009
    Xueliang Chai
    Abstract The karyotype and chromosomal characteristics of the yellowtail kingfish Seriola lalandi lalandi were investigated by examining metaphase spreads from kidney cells of 4-month-old fish artificially bred using wild-captured broodstock from the coast of South Australia. A total of 80 mitotic metaphases from 10 individual fish were analysed, with 52 spreads having a mode of 2n=48 chromosomes, representing 65% of the metaphases observed. The diploid consisted of two metacentric, two submetacentric, six subtelocentric and 38 telocentric chromosomes, with the fundamental number of chromosome arms being 52. The total haploid chromosome length was approximately 44.412 ,m. This study shows that the karyotype of S. lalandi lalandi differs from those reported previously for other Seriola species in having one pair of metacentric chromosomes. [source]


    Measurement of total body composition changes of common carp by computer tomography

    AQUACULTURE RESEARCH, Issue 12 2003
    Csaba Hancz
    Abstract The crude fat and protein content of the total body was estimated by X-ray computer tomography (CT) and determined by chemical analyses during a feeding experiment with sexually matured common carp. Between 21 and 35 serial scans were taken of altogether 41 fish and samples from the homogenized body were prepared for chemical analyses. Experimental fish with an average body weight of 1453 g originated from a commercial stock of mirror carp. Two feeding regimes (carp feed and carp feed+ad libitum maize) were applied for 57 days and followed by a fasting period of 27 days. Both feeding regimes significantly increased the crude fat content of the whole body that did not decrease during fasting in spite of high water temperature (22°C). No significant changes were observed in crude protein content. The variables used for producing the prediction equations were taken from the density values of the Hounsfield scale, on a range between ,90 and +160, by summing the frequencies within each interval of 10 values. Whole body fat content could be estimated with R2=0.89,0.91 accuracy with the principal component analysis using data of all (seven) body regions and only dorsal fin region respectively. Adequate linear regression model could not be calculated by the same procedure for crude protein. Three-dimensional ,volumetric' estimation of fat tissue was also carried out on the basis of fat index showing high correlation with measured fat content. The changes of body composition of individual fish can be followed by sequential CT scanning. [source]


    Movement of sonically tagged bluespine unicornfish, Naso unicornis, in relation to marine reserve boundaries in Rodrigues, western Indian Ocean

    AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2010
    Emily Hardman
    Abstract 1.The lagoon fishery of Rodrigues has considerable socio-economic importance; however, catches have declined by 50% in recent years. The bluespine unicornfish, Naso unicornis (Forsskĺl 1775) is an important component of the fishery. 2.To begin to assess whether marine reserves might benefit this species, sonic telemetry was used to track individual fish in one of Rodrigues' four marine reserves. Seven unicornfish were caught in the Grand Bassin reserve and tagged with abdominally implanted acoustic tags. 3.Over a period of 57 days their locations were determined up to 21 times using a hand held hydrophone and receiver. Individual minimum convex polygon (MCP) home ranges varied from ,10 000,m2 to ,274,000,m2 and were not correlated with fish size. Kernel estimates of core areas (50% utilization distribution) varied from ,5000,m2 to ,175,000,m2. All seven fish stayed within the marine reserve and the largest home range occupied less than ,2% of the area of the marine reserve. 4.Fish remained on the outside edge of the lagoon on the shallow reef slope and among coral patches. These findings suggest that bluespined unicornfish biomass and numbers should increase if the Grand Bassin marine reserve is closed to fishing. Long-term monitoring will, however, be required to demonstrate this outcome. Copyright © 2010 John Wiley & Sons, Ltd. [source]


    Lipid damage during frozen storage of Gadiform species captured in different seasons

    EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 6 2007
    Santiago P. Aubourg
    Abstract Quality loss of two gadiform fish species (blue whiting, Micromesistius poutassou; hake, Merluccius merluccius) during frozen storage (,30 and ,10,°C; up to 12,months) was studied. For this, hydrolytic (formation of free fatty acids, FFA) and oxidative (conjugated dienes, peroxide and interaction compound formation) lipid damage were analysed. For both species, individual fishes captured in two different trials (May and November) were considered. Increasing (p,<0.05) lipid hydrolysis and oxidation (peroxide and interaction compound formation) were observed for all kinds of samples throughout the frozen storage. Interaction compound detection by fluorescence analysis showed the best correlation values with storage time. Some higher (p,<0.05) hydrolysis development could be observed in hake captured in May than in its counterpart from the November trial, while frozen blue whiting did not provide definite differences for FFA formation between both trials. Concerning peroxide formation, higher (p,<0.05) values were obtained for individual blue whiting and hake captured in November when compared to their corresponding May fish for both frozen storage conditions. Interaction compound formation was also found to be higher (p,<0.05) for November hake fish than for its counterpart captured in May, while blue whiting did not provide definite differences between trials. [source]


    Jordan's and other ecogeographical rules, and the vertebral number in fishes

    JOURNAL OF BIOGEOGRAPHY, Issue 3 2008
    R. M. McDowall
    Abstract Aim, To explore variation in the number of vertebrae in fishes in the context of Jordan's rule and other ecogeographical rules. Location, Global. Methods, The study is based on literature review. Results, The number of vertebrae varies very widely across the diversity of fishes. Jordan's rule states that vertebral number increases with latitude, and this is widely attributed to ambient temperatures during ontogeny of individual fishes. However, the number of vertebrae may depend on both the ontogenetic environment and inheritance. Diverse other aspects of fish development and ecology are suggested as influencing vertebral number, including fish size, phyletic position, body shape and swimming mode. Main conclusions, The number of different factors that influence the number of vertebrae in fishes makes for highly complex patterns of variation, and means that unravelling causes is difficult. The question needs to be addressed at the population/species/species group scale; moreover, the lack of discrimination between environmental and inherited causes of variation adds to the complexity. [source]


    Contrasting pragmatic and suffering-centred approaches to fish welfare in recreational angling

    JOURNAL OF FISH BIOLOGY, Issue 10 2009
    R. Arlinghaus
    Two views dealing with fish welfare in recreational fishing are discussed in an effort to stimulate the current discourse on the topic. The pragmatic approach asks whether and how strongly recreational fishing compromises the health and fitness of individual fishes and what can be done to avoid or mitigate such effects. Its implementation rests on accepting recreational fishing as a principally legitimate activity. The second approach to fish welfare focuses on suffering and pain in fishes and is usually morally prescriptive. Its central tenet is that some or all recreational fishing practices may be unacceptable unless sufficient benefits to humans are created, which justify the supposedly cruel treatment of the fishes. The pragmatic approach to fish welfare is preferred because it relies on objectively measurable variables of impaired fish welfare (e.g. physiological, behavioural or fitness indicators) and does not question recreational fishing on moral grounds. Contrary to a suffering-centred approach to fish welfare, a pragmatic perspective emphasizes positive messages and facilitates constructive dialogue among stakeholders. In contrast, a suffering-centred approach to fish welfare tends to promote tension and enduring conflict that cannot be reconciled objectively and thus should be avoided. [source]