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Fish Size (fish + size)
Kinds of Fish Size Selected AbstractsThe sampling efficiency of electrofishing for Neogobius species in a riprap habitat: a field experimentJOURNAL OF APPLIED ICHTHYOLOGY, Issue 5 2008M. Pola Summary Even though electrofishing is commonly used to sample Neogobius spp. and other swimbladder-lacking benthic fishes, its efficiency is considered poor especially in habitats with abundant interstitial spaces. To determine the efficiency of electrofishing Neogobius spp. and quantitatively estimate sampling bias in a riprap (shot rock used to armor shorelines against water erosion) mesohabitat, riprap fragments were set up in a natural riverine environment. The experimental setting enabled us to collect all fish remaining in the riprap fragments after these areas had been electrofished. The sampling efficiency of electrofishing Neogobius spp. (dominated by Neogobius melanostomus) varied between 17.6 and 47.4% (mean 29.7%), while percids (possessing a well-developed swim bladder) were collected with 74.6% efficiency. Fish size had no effect on the probability of capturing Neogobius spp. by electrofishing. Within Neogobius spp., N. melanostomus was less susceptible to electrofishing than Neogobius gymnotrachelus (23.7% and 50.1%, respectively). Decreased electrofishing efficiency in areas of rocky substrate should be considered in estimates of total abundance of Neogobius spp., especially if they are to be compared with catches of other species possessing swim bladders. [source] Estimating digestible protein requirements of silver perch, Bidyanus bidyanus MitchellAQUACULTURE RESEARCH, Issue 5 2001G L Allan Abstract In this study, we estimated requirements for digestible protein, using intact protein sources, at one digestible energy content. Using digestibility data for silver perch (Bidyanus bidyanus Mitchell) for a large number of ingredients, we formulated a ,summit' diet to contain between 1.4 and 1.8 times the ,expected requirements' for digestible essential amino acids (based on requirements for channel catfish, Ictalurus punctatus Rafinesque). A ,diluent' diet was formulated to contain 0.4,0.5 times the expected requirements of digestible essential amino acids. Both ,summit' and ,diluent' diets contained similar digestible energy (14.7 MJ digestible energy kg,1 for the summit and 13.4 MJ digestible energy kg,1 for the diluent). Six diets were prepared with the following amounts of summit,diluent diets: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100. A practical diet widely used by commercial farmers was also included as a control. Ten juvenile fish (2.1,2.6 g) were stocked into each experimental 70-L acrylic aquarium, and each dietary treatment was randomly assigned to five replicate aquaria. Fish were fed twice daily to apparent satiation for 54 days. Final individual fish weight ranged from 4,15.5 g. Results were analysed using intersecting linear regression analysis. The optimum digestible dietary protein for diets with 13.4,14.7 MJ digestible energy kg,1, after which protein deposition did not increase significantly, was 28%. Although this study did not determine requirements for individual amino acids, for diets with the digestible energy content used here, requirements for individual amino acids obviously did not exceed the content in the 28% protein diet. These contents are useful as an estimate of ,recommended levels' for silver perch diets with 13.4,14.7 MJ digestible energy kg,1. The proximate composition of fish was affected by diet. Whole body protein and moisture increased, whereas lipid content decreased with increasing dietary protein content (and increasing protein,energy ratio and decreasing lipid). Fish size was also affected by diet; however, the changes in whole carcass proximate composition also occurred for fish fed diets 60:40, 80:20 and the summit diet which were a similar final weight. [source] Density-dependent growth of young-of-the-year Atlantic salmon (Salmo salar) revisitedECOLOGY OF FRESHWATER FISH, Issue 1 2010I. Imre Imre I, Grant JWA, Cunjak RA. Density-dependent growth of young-of-the-year Atlantic salmon (Salmo salar) revisited. Ecology of Freshwater Fish 2010: 19: 1,6. © 2009 John Wiley & Sons A/S Abstract,,, The length of individual young-of-the-year (YOY) Atlantic salmon (Salmo salar) in Catamaran Brook decreases with increasing population density following a negative power curve. Because most of this decrease in growth rate occurs at low densities (<1 fish·m,2), (Imre et al. 2005; Journal of Animal Ecology, 74: 508,516) suggested that exploitation competition for drifting prey rather than space limitation might be responsible for this pattern. Recently, (Ward et al. 2007; Journal of Animal Ecology, 76: 135,138) showed that the negative power curve of growth rate versus density can be caused by other mechanisms and suggested that Imre et al.'s evidence for density-dependent growth would have been stronger if we had analysed final size versus initial density rather than final density. We examined (i) whether the negative power curve of size versus density was also apparent in an analysis of final size versus initial density and tested two predictions that emerge from Ward et al.'s model, (ii) the variance in body size increases with population density, and (iii) the maximum fish size at a site is density-independent. The final size of YOY salmon decreased with increasing initial density following a negative power curve. Our data did not provide strong support for the above predictions emerging from Ward et al.'s model. Our analyses of different years, sites and seasons were consistent with the hypothesis of density-dependent growth of YOY salmon. [source] Movements of Murray cod (Maccullochella peelii peelii) in a large Australian lowland riverECOLOGY OF FRESHWATER FISH, Issue 4 2009J. D. Koehn Abstract,,, This study of Murray cod (Maccullochella peelii peelii) movements in a large lowland river in south-eastern Australia indicated that the species was not sedentary, but undertook complex movements that followed a seasonal pattern. While there were sedentary periods with limited home ranges and high site fidelity, Murray cod also under took larger movements for considerable portions of the year coinciding with its spawning schedule. This generally comprised movements (up to 130 km) from a home location in late winter and early spring to a new upstream position, followed by a rapid downstream migration typically back to the same river reach. Timing of movements was not synchronous amongst individuals and variation in the scale of movements was observed between individuals, fish size, original location and years. [source] Testing the ability of habitat selection theory to predict interannual movement patterns of a drift-feeding salmonidECOLOGY OF FRESHWATER FISH, Issue 1-2 2000N. F. Hughes Abstract , This article extends the logic of a habitat selection model (Hughes, Ecology, 1998) to make predictions about the way body size will influence the probability that fish will make a long distance interannual movement, from the feeding position it occupies in one summer to the position it occupies the next. The model predicts that the probability of this kind of movement will fall as fish grow and reach zero for the largest fish in the population. I tested these predictions using data on Arctic grayling Thymallus arcticus in the lower 140 km of a 260-km-long interior Alaskan river. Both predictions of the model were well supported by the data. As expected, the probability a fish will make a long-distance interannual movement decreased with fish size, and the largest fish in the population had a movement probability of zero., [source] Long-term trends in liver neoplasms in brown bullhead in the Buffalo River, New York, USAENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2010Darrel J. Lauren Abstract The Buffalo River area of concern (AOC) was assigned an impaired status for the fish tumors and other deformities beneficial use impairment category by the New York State Department of Environmental Protection in 1989. This was initially based on an inadequately documented brown bullhead (Ameiurus nebulosus) feeding study using river sediment extracts. The presence of liver tumors was subsequently supported by reports of a 19 to 27% prevalence in wild brown bullhead between 1983 and 1988 and a 4.8% prevalence in 1998. However, neither fish size (or age) nor sample locations were given, and histopathological definitions were inconsistent in these previous studies. Therefore, in 2008, we re-evaluated the prevalence of hepatocellular and chloangiocellular tumors (as well as other gross indicators of fish health) in brown bullhead averaging 25,cm in length collected from three reaches of the Buffalo River and recorded our collection sites by global positioning system. Among the 37 fish of appropriate size collected, only three exhibited liver tumors (8%). The tumors were evenly distributed within the three reaches, and only hepatocellular tumors were found. There were no differences in the prevalence of hepatic foci of alteration, body weight, length, or hepatosomatic index among the three reaches, but the conditions factor was significantly lower in fish from reach 2. Natural attenuation of water and sediment quality are the most likely causes for the decrease in liver tumors. The prevalence of liver tumors between 1998 and 2008 in the Buffalo River is similar to that found in recovery-stage AOCs and some Great Lakes reference areas. Environ. Toxicol. Chem. 2010; 29:1748,1754. © 2010 SETAC [source] Dichlorodiphenyltrichloroethane in the aquatic ecosystem of the Okavango Delta, Botswana, South AfricaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2003Bontle Mbongwe Abstract Concentrations of DDT and its metabolites were measured in water, plants, invertebrates, and fish from lagoons in the Okavango Delta, Botswana (Africa), where DDT has been used for approximately 50 years. The sampling area was sectioned to distinguish spraying for malaria and for African sleeping sickness. Average concentrations of total DDT (sum of DDT and its metabolites) in the Okavango ranged from 0.009 ng/L in water to 18.76 ng/g wet weight in fish. These levels are approximately 1% of those found in piscivorous fish from temperate North America. The dichlorodiphenyl ethylene (DDE) metabolite was the most abundant fraction of total DDT. Although total DDT concentrations were higher in areas treated for malaria than areas treated for sleeping sickness, these concentrations were likely driven by factors other than the historic application of the pesticide. Equilibration with air concentrations is the most likely explanation for these levels. Since the mean annual temperature exceeds the temperature of vaporization of DDT, this research points to the need for reliable transport models. Our results showed that total DDT concentration in fish was best explained by lipid content of the fish and trophic position inferred by ,15N, regardless of DDT application history in those areas. The reservoir above Gaborone Dam, an area downstream of the Okavango but where DDT had not been used, was sampled to compare total DDT levels to the treated areas. The two species (a herbivorous threespot talapia and the omnivorous sharptooth catfish) from Gaborone had levels higher than those found in the Okavango Delta, but these differences can again be explained using trophic position inferred by ,15N rather than by fish size or location. [source] Ontogeny of Acoustic and Feeding Behaviour in the Grey Gurnard, Eutrigla gurnardusETHOLOGY, Issue 3 2005M. Clara P. Amorim Although sound production in teleost fish is often associated with territorial behaviour, little is known of fish acoustic behaviour in other agonistic contexts such as competitive feeding and how it changes during ontogeny. The grey gurnard, Eutrigla gurnardus, frequently emits knock and grunt sounds during competitive feeding and seems to adopt both contest and scramble tactics under defensible resource conditions. Here we examine, for the first time, the effect of fish size on sound production and agonistic behaviour during competitive feeding. We have made sound (alone) and video (synchronized image and sound) recordings of grey gurnards during competitive feeding interactions. Experimental fish ranged from small juveniles to large adults and were grouped in four size classes: 10,15, 15,20, 25,30 and 30,40 cm in total length. We show that, in this species, both sound production and feeding behaviour change with fish size. Sound production rate decreased in larger fish. Sound duration, pulse duration and the number of pulses increased whereas the peak frequency decreased with fish size, in both sound types (knocks and grunts). Interaction rate and the frequency of agonistic behaviour decreased with increasing fish size during competitive feeding sessions. The proportion of feeding interactions accompanied by sound production was similar in all size classes. However, the proportion of interactions accompanied by knocks (less aggressive sounds) and by grunts (more aggressive) increased and decreased with fish size, respectively. Taken together, these results suggest that smaller grey gurnards compete for food by contest tactics whereas larger specimens predominantly scramble for food, probably because body size gives an advantage in locating, capturing and handling prey. We further suggest that sounds emitted during feeding may potentially give information on the motivation and ability of the individual to compete for food resources. [source] Size-independent age effects on reproductive effort in a small, short-lived fishFRESHWATER BIOLOGY, Issue 5 2008PABLO A. TEDESCO Summary 1. Age-related changes in reproductive effort have been predicted by theoretical models and observed in a wide range of organisms. However, for indeterminate growers such as fish, an allometric relationship linking gonad weight to body size is commonly observed. There is often a positive linear relationship when these variables are log-transformed, which by implication reduces the influence of age on reproductive effort. 2. Contrasting with this usual pattern, we report a nonlinear relationship between gonad weight and fish size (after log-transformation) in mosquitofish (Gambusia holbrooki), clearly resulting from age changes. The declining rate of increase of gonad mass as a function of body size revealed a higher reproductive effort for younger individuals relative to size. 3. This size-independent age effect on reproductive effort was predicted based on previous studies of mosquitofish and is certainly related to their particular life-history strategy, combining an early maturation and short lifespan with the physiological costs of reproduction and over-wintering. Our findings probably apply to other small, short-lived species with similar life history. [source] The use of size,frequency diagrams to characterize prehistoric fish catches and to assess human impact on inshore fisheriesINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 1-2 2001Foss Leach Abstract Archaeological collections of fish bones from previously excavated sites in New Zealand are being re-examined and selected bones measured in order to estimate original fish size, reconstruct prehistoric fish catches and assess human impact on the fishery over the course of about 800 years of New Zealand prehistory. Several problems hamper this research, such as small sample sizes, lack of significant stratigraphy at many sites, inconsistent field collection strategies and failure to retain all of the material after initial analysis. Although some common fish species show a significant decline in mean size between pre-European and early historic samples on the one hand, and modern populations on the other, we have found little support for the common belief that there was a decline in mean fish size during the pre-European period. We have observed increases over time in the mean size of snapper (Pagrus auratus), blue cod (Parapercis colias) and undifferentiated species of Labridae from several sites scattered throughout New Zealand. Distinguishing between changes in fish population structures owing to natural processes, such as surface sea water changes, and those which are the result of human over-fishing is not simple, because both processes can operate simultaneously. We draw on modern fish quota management models to separate these processes. Important factors for each species are inshore biomass and the recruitment rate at different temperature regimes. In the case of blue cod, we find that there are signs in the catch diagrams of changes in fishing technology, and that 30,80% of catches are undersized fish in terms of modern management criteria. Copyright © 2001 John Wiley & Sons, Ltd. [source] Distribution patterns of fish biomass by acoustic survey in three Tunisian man-made lakesJOURNAL OF APPLIED ICHTHYOLOGY, Issue 3 2010I. Djemali Summary In order to test the hypothesis that fish distribution is related to water depth, three exploited reservoirs were sampled at day and at night using a Simrad EK60 echosounder. Acoustic surveys were carried out between February and June 2008, which focused on the fish size, species density (fish per ha) and biomass (kg ha,1) along vertical and longitudinal gradients. It was evident in the surface layer (0,3 m) during daytime that the larger fish sizes occupy waters near the dam or the middle of Lakhmess and Sejnane reservoirs. In the upper layer at nighttime, a gradient of fish size is shown proportional to the depth at Lakhmess Reservoir and inversely proportional at the man-made Sejnane Lake. At Lakhmess and Laabid reservoirs, fish density was significantly higher in deep water (3926 ± 1409 and 624 ± 258 fish per ha) rather than in the upper layer (988 ± 2 and 8 ± 2 fish per ha in daytime, respectively), while at Sejnane Reservoir the number of fish per area was similar along the vertical gradient. The biomass was significantly higher in waters deeper than 3 m at Sejnane Reservoir whereas at Lakhmess it was higher in the surface layer. Fish biomass increased from upstream (0.16 ± 0.05 kg ha,1) to middle (3.07 ± 2.96 kg ha,1) and downstream (3.82 ± 2.30 kg ha,1 at night) areas in the man-made Laabid Lake while a similar longitudinal gradient occurred in the deepest Sejnane Reservoir. The vertical gradient in fish distribution is discussed. From the dam to the tributary of the entire water column, it was concluded that fish biomass distribution was governed by depth and was most abundant in areas with deep waters. [source] The diet of blue whiting, hake, horse mackerel and mackerel off PortugalJOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2002H. N. Cabral This paper deals with the diets of blue whiting Micromesistius poutassou (Risso 1810), hake Merluccius merluccius (L. 1758), horse mackerel Trachurus trachurus (L. 1758), and mackerel Scomber scombrus (L. 1758) off Portugal and explores variations in fish length, water depth, latitude and season. All four species feed on fish; however, hake and mackerel are the first and second most important predators, respectively, blue whiting being the most important fish prey for both species. The diets of blue whiting and horse mackerel are composed mainly of crustaceans. Diet variations according to predator fish size are more important than either latitude or depth. In the diets of blue whiting, hake and horse mackerel, prey importance increases with predator size. For blue whiting and horse mackerel, diet variations with fish length and water depth are correlated: small fish are closely associated with coastal areas where they feed on copepods and decapod larvae. Seasonality in the diet is apparent for blue whiting, hake and mackerel. For blue whiting, the decapod Pasiphaea sivado is the most important prey in summer and autumn, being replaced by the euphausid Meganyctiphanes norvegica in winter. In the diet of hake, seasonality was characterised by the major importance of Macroramphosus scolopax in autumn, whereas the diet of mackerel consisted of zooplankton in summer, fish and decapods in autumn and decapod larvae in winter. Seasonal changes in the diet of horse mackerel correspond to a higher diversity of prey in autumn compared to other seasons (although euphausids are the main prey in all seasons). Seasonality in feeding activity is not as marked for the other species as it is for horse mackerel; the percentage of empty stomachs of horse mackerel is greatest in winter, when spawning takes place at the Portuguese coast. [source] Jordan's and other ecogeographical rules, and the vertebral number in fishesJOURNAL OF BIOGEOGRAPHY, Issue 3 2008R. 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] Effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii determined by acoustic telemetryJOURNAL OF FISH BIOLOGY, Issue 3 2010Y. Kawabata The effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii were examined using acoustic telemetry. Nine fish were released in Urasoko Bay, Ishigaki Island, Japan, in September 2006, and another nine were released in June to July 2007, before a cyclone's passing through the area in September 2007. Data for the fish released in 2006 were used as the cyclone-inexperienced group to compare their distribution pattern to that of the 2007 cyclone-experienced group. Both groups of fish were monitored for up to 150 days. Of the nine fish in each group, four (44%) and two (22%) were monitored for over 150 days in the cyclone-inexperienced and the cyclone-experienced groups, respectively. Three of the five fish that had settled in the monitoring area left the area within a few days of the cyclone event. To estimate the time of disappearance of the fish, maximum wind speed during a period of 7 days (indicating the occurrence and intensity of the tropical cyclone), fish size and release year were evaluated as explanatory variables using a Cox proportional hazards model with Akaike's information criterion. The best predictive model included the effect of maximum wind speed. One fish that left the monitoring area displayed movement patterns related to strong winds, suggesting that wind-associated strong currents swept the fish away. No relationships were found between the movement patterns of the other two fish and any physical environmental data. The daily detection periods of one of the two fish gradually decreased after the cyclone hit, and this fish eventually left the monitoring area within 3 days, suggesting that it shifted to a habitat outside the monitoring area. These results indicate that tropical cyclones have both direct and indirect effects on the distribution of hatchery-reared C. schoenleinii. [source] A review of the likely effects of climate change on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta, with particular reference to water temperature and flowJOURNAL OF FISH BIOLOGY, Issue 10 2009B. Jonsson The present paper reviews the effects of water temperature and flow on migrations, embryonic development, hatching, emergence, growth and life-history traits in light of the ongoing climate change with emphasis on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta. The expected climate change in the Atlantic is for milder and wetter winters, with more precipitation falling as rain and less as snow, decrease in ice-covered periods and frequent periods with extreme weather. Overall, thermal limits for salmonids are species specific. Scope for activity and growth and optimal temperature for growth increase with temperature to an optimal point before constrain by the oxygen content of the water. The optimal temperature for growth decreases with increasing fish size and varies little among populations within species, whereas the growth efficiency may be locally adapted to the temperature conditions of the home stream during the growth season. Indirectly, temperature influences age and size at smolting through its effect on growth. Time of spawning, egg hatching and emergence of the larvae vary with temperature and selective effects on time of first feeding. Traits such as age at first maturity, longevity and fecundity decrease with increasing temperature whilst egg size increases with temperature. Water flow influences the accessibility of rivers for returning adults and speed of both upstream and downstream migration. Extremes in water flow and temperature can decrease recruitment and survival. There is reason to expect a northward movement of the thermal niche of anadromous salmonids with decreased production and population extinction in the southern part of the distribution areas, migrations earlier in the season, later spawning, younger age at smolting and sexual maturity and increased disease susceptibility and mortality. Future research challenges are summarized at the end of the paper. [source] Can seasonal home-range size in pike Esox lucius predict excursion distance?JOURNAL OF FISH BIOLOGY, Issue 4 2008C. M. Knight The hypothesis that vagility, or tendency to move, in pike Esox lucius can be predicted from individual home range was tested using telemetry. Independently of fish size, mean annual excursion distance was positively correlated to winter (0·02,0·95 ha) and spring (0·02,0·59 ha) home ranges but not summer and autumn home ranges. [source] A hydro-mechanical approach to the scaling of swimming performance in the sand flathead Platycephalus bassensis Cuvier: effects of changes in morphological features based on fish sizeJOURNAL OF FISH BIOLOGY, Issue 6 2007K. Yanase The swimming performance of Platycephalus bassensis at steady speed was assessed with an emphasis on hydrodynamics. The minimum swimming speed to maintain hydrostatic equilibrium for P. bassensis of 0·271 m total length (LT) was calculated to be 1·06 LT s,1. At this speed, the required lift to support the mass of the fish was equivalent to 6·6% of the fish mass; 82·7% of which was created by the body as a hydrofoil, and the rest of which was created by the pelvic fins as hydrofoils. The minimum swimming speed decreased with the LT of the fish and ranged from 1·15 LT s,1 for a fish of 0·209 m to 0·89 LT s,1 for a fish of 0·407 m. The forward movement per tail-beat cycle (i.e. stride length) was described with an equation including quantities of morphological and hydro-mechanical relevance. This equation explained that stride length was increased by the effect of turbulence characterized by the Reynolds number and demonstrated the morphological and hydro-mechanical functional design of the fish for maximizing thrust and minimizing drag. The larger span of the caudal fin and caudal tail-beat amplitude was associated with larger stride length, whereas greater frictional drag was associated with smaller stride length. [source] Factors affecting river entry of adult Atlantic salmon in a small riverJOURNAL OF FISH BIOLOGY, Issue 4 2007B. Jonsson In this study, effects of stock origin, fish size, water flow and temperature on time of river ascent of adult Atlantic salmon Salmo salar were tested. Brood stocks were collected in eight Norwegian rivers situated between 59 and 69° N. The fish were reared to smolts, individually tagged and released in the River Imsa, south-west Norway (59° N). Adults from all stocks approached the Norwegian coast concurrently, but Atlantic salmon ,70 cm in natural tip length entered coastal water slightly earlier during summer than smaller fish. Atlantic salmon <70 cm, however, ascended the river significantly earlier and at lower water flow and higher water temperature than larger fish. Although largest in size, the fish from the northern populations (62,69° N) ascended the River Imsa almost 1 month earlier than those from the south (59,60° N). They seemed less restricted by the environmental factors than the fish originating from the more southern rivers. There was no apparent trend among years in time of river ascent. Maximum ascent per day occurred at water discharges between 12·5 and 15 m3 s,1 and at water temperatures between 10 and 12·5° C. There was a significant positive correlation between water flow and river ascent during the first part of the upstream run from July to September with best correlation for September, when multiple regression analysis indicated that water temperature had an additional positive effect. Stock origin, fish size and water discharge were important variables influencing the upstream migration of Atlantic salmon in small rivers. [source] Ultraviolet absorbance of the mucus of a tropical damselfish: effects of ontogeny, captivity and diseaseJOURNAL OF FISH BIOLOGY, Issue 6 2006J. P. Zamzow The ultraviolet (UV) absorbance of the mucus of a Great Barrier Reef damselfish Pomacentrus amboinensis was investigated with regard to ontogeny and time spent in captivity. The UV absorbance of P. amboinensis mucus increased with fish size and decreased with time spent in captivity. The wavelength of maximum absorbance of the mucus did not change with fish size, but shifted towards shorter wavelengths with increasing time spent in captivity. The UV absorbance of the mucus of fish with ,fin rot' was compared to that of similar healthy individuals, and a significant decrease in UV absorbance of unhealthy fish mucus was detected; no wavelength shifting occurred. Pomacentrus amboinensis appears to sequester mycosporine-like amino acids from the diet in order to protect epithelial tissues from UV damage, and decreases in UV absorbance in captive fish were probably due to insufficient dietary availability. [source] Swimming performance and metabolism of 0+ year Thymallus arcticusJOURNAL OF FISH BIOLOGY, Issue 4 2005L. A. Deegan The prolonged swimming speed and metabolic rate of 0+ year Arctic grayling Thymallus articus were examined with respect to current velocity, water temperature and fish size, and compared to conditions fish occupy in the river. Oxygen consumption (mg O2 h,1) increased with fish mass and temperature (6,23° C), with a steep increase in metabolic rate between 12 and 16° C. Absolute prolonged swimming speed (cm s,1) increased rapidly with fish size (total length, LT, and mass), however, fish in the natural stream habitat occupied current velocities between 15 and 25 cm s,1 or 4 LT s,1, approximately half their potential prolonged swimming speed (10 LT s,1). [source] Effects of fish size, time-to-fatigue and turbulence on swimming performance: a case study of Galaxias maculatusJOURNAL OF FISH BIOLOGY, Issue 6 2003V. I. Nikora A simple relationship for the inanga Galaxias maculatus swimming velocity is suggested and tested in low and high turbulence channels. The relationship connects the swimming velocity with fish Reynolds and Froude numbers and can be used in both ecological analysis (e.g. habitat requirements) and management strategies (e.g. fishways design). Contrary to some previous studies and intuition, effects of turbulence on swimming performance appeared to be negligible. The most likely explanation for this result relates to mechanics of fish,turbulence interactions that may be dependent on both the turbulence scales and energy. The data suggest that future studies of turbulence effects on fish behaviour should involve, in addition to turbulence energetics, consideration of fish dimensions in relation to the spectrum of turbulence scales. [source] Laboratory evaluation of two bioenergetics models applied to yellow perch: identification of a major source of systematic errorJOURNAL OF FISH BIOLOGY, Issue 2 2003P. G. Bajer Laboratory growth and food consumption data for two size classes of age 2 year yellow perch Perca flavescens, each fed on two distinct feeding schedules at 21° C, were used to evaluate the abilities of the Wisconsin (WI) and Karas,Thoresson (KT) bioenergetics models to predict fish growth and cumulative consumption. Neither model exhibited consistently better performance for predicting fish body masses across all four fish size and feeding regime combinations. Results indicated deficiencies in estimates of resting routine metabolism by both models. Both the WI and KT models exhibited errors for predicting growth rates, which were strongly correlated with food consumption rate. Consumption-dependent prediction errors may be common in bioenergetics models and are probably the result of deficiencies in parameter values or assumptions within the models for calculating energy costs of specific dynamic action, feeding activity metabolism or egestion and excretion. Inter-model differences in growth and consumption predictions were primarily the result of differences in egestion and excretion costs calculated by the two models. The results highlighted the potential importance of parameters describing egestion and excretion costs to the accuracy of bioenergetics model predictions, even though bioenergetics models are generally regarded as being insensitive to these parameters. The findings strongly emphasize the utility and necessity of performing laboratory evaluations of all bioenergetics models for assurance of model accuracy and for facilitation of model refinement. [source] Sediment preferences and size-specific distribution of young-of-the-year Pacific halibut in an Alaska nurseryJOURNAL OF FISH BIOLOGY, Issue 3 2002A. W. Stoner A combination of laboratory experiments and field surveys was used to test the hypotheses that responses to sediments change with fish size and that sediment grain-size is the predominant environmental factor affecting small-scale distribution in young-of-the-year (yoy) Pacific halibut Hippoglossus stenolepis. Laboratory tests showed that the smallest fish (31,40 mm LT) chose fine sediments (muddy and fine sands), fish 51,70 mm had high selectivity (primarily medium sand), and the largest fish (80,150 mm) were not selective although they avoided the largest grain-sizes (pebbles and granules). Sediment preferences were correlated with size-dependent burial capabilities. Beam trawl collections were made over a 6 year period in Kachemak Bay, Alaska, to examine the distribution of yoy Pacific halibut (14,120 mm LT) using small size classes (e.g. 10 mm intervals). Canonical correlation analysis showed that the per cent of sand in the sediment was a highly significant variable for all but one size and date combination. Catch per unit of effort (CPUE) for newly settled fish (<30 mm LT) was highest on very fine sand, fish 41,80 mm were most abundant on fine sand, and the largest yoy fish (81,120 mm) were abundant over a range of sediments from fine sand to mud. Except for the smallest fish, Pacific halibut in the field were associated with sediments somewhat finer than predicted from the laboratory experiments; however, virtually all were captured where they could bury easily. The ability of flatfish to bury and shelter in sediment is related to fish size; consequently, habitat associations shift rapidly during the first year of life. Habitat models for yoy flatfishes should consider size-dependent shifts in capabilities and preferences. [source] Effects of Ligula intestinalis on habitat use, predation risk and catchability in European minnowsJOURNAL OF FISH BIOLOGY, Issue 4 2001J. Museth The frequency of infection with Ligula intestinalis (Cestoda) in European minnow Phoxinus phoxinus, in a subalpine lake in Eastern Norway, did not differ between vegetated shoreline, exposed shoreline and non-vegetated localities >50 m from the shoreline. There was no difference in the vertical distribution of infected and uninfected individuals. The frequency of infection was higher among minnows in brown trout Salmo trutta stomachs than among those obtained by gillnets and minnow traps, suggesting that brown trout selectively preyed on infected minnows. Prevalence of infection decreased with increasing fish size, probably due to selective mortality among parasitized individuals. Within a given length-class, minnows captured by different sections of multi-mesh gillnets showed a significant increase in the frequency of infection with increasing mesh-size. Apparently, parasitized individuals had a higher catchability in gillnets due to increased girth caused by the plerocercoid in the body cavity. This may partly explain why the observed prevalence of infection was several times higher among minnows captured by gillnets than by minnow traps. [source] Seasonal pattern of depth selection in smallmouth bassJOURNAL OF ZOOLOGY, Issue 2 2009C. D. Suski Abstract The current study used a stationary acoustic telemetry array to monitor the depth selection of adult smallmouth bass Micropterus dolomieu in a large, oligotrophic lake in Ontario, Canada. At an annual scale, smallmouth bass demonstrated regular, seasonal changes in inhabited depths: fish occupied shallow water during the summer (2,5 m depth) and descended to deeper water (12,15 m depth) during winter under ice. Smallmouth bass remained above the thermocline in the summer, seasonal depth patterns did not vary across fish size and movements to and from seasonal depths were closely linked to the development and degradation of the thermocline. At finer time scales, smallmouth bass exhibited diel vertical migrations in summer, with fish moving to <2 m at night, and then descending to 3,5 m during the day. This pattern remained constant during the summer period examined, and varied with size such that larger fish remained deeper than smaller fish. During winter, depth did not vary across the 3-month monitoring period (c. 14 m), but small (<2 m) changes in depth were observed periodically, suggesting limited movements were occurring. Results are further discussed in the context of climate change and reproductive success for this species. [source] Influence of dietary protein levels on growth performance and body composition of African bonytongue fingerlings, Heterotis niloticus (Cuvier, 1829)AQUACULTURE NUTRITION, Issue 2 2010S.-E. MONENTCHAM Abstract Two experiments were conducted to examine the influence of dietary protein levels on growth and carcass proximate composition of Heterotis fingerlings. Four isoenergetic practical diets were formulated to contain dietary protein levels from 250 to 400 g kg,1 diet. Replicate groups of young Heterotis (initial live weight 3.96 and 26.40 g in experiments 1 and 2 respectively) were handfed twice daily to apparent satiation for a period of 42 and 28 days respectively. Statistical analysis revealed that growth rate was significantly affected by dietary protein level (P < 0.01). The highest weight gain was observed in fingerlings fed with 300 and 350 g protein kg,1 diet for fish size ranging between 3,15 and 26,62 g respectively. There was no significant difference between groups fed with 300, 350 and 400 g protein kg,1 diet for Heterotis fingerlings (3,15 g) in the one hand; in the other hand, significant differences were found between fish (26,62 g) fed with 350 g protein kg,1 diet and those receiving 300 and 400 g protein kg,1 diet, with no significant difference between each other. The specific growth rate varied from 2.4% to 3.1% day,1. The whole-body protein, lipid, moisture and ash contents were not significantly affected by dietary protein levels (P > 0.05). The relationships between percentage weight gain and dietary protein levels suggested very similar dietary protein requirement (about 310 g crude protein kg,1 diet) for Heterotis ranging from 3 to 62 g. The maximum growth occurred at about 345 g protein kg,1 diet. [source] Improving the mechanical characteristics of faecal waste in rainbow trout: the influence of fish size and treatment with a non-starch polysaccharide (guar gum)AQUACULTURE NUTRITION, Issue 3 2009A. BRINKER Abstract This study (3 × 2 randomized factorial design) describes differences in the mechanical properties of faeces from rainbow trout of three size classes (small ,40 g, mid-size ,150 g, large ,650 g) and assesses the effects of a non-starch polysaccharide binder (guar gum). Observations made at the macroscopic level were reinforced by rheological measurements of viscosity and elastic modulus. Mid-sized fish excreted mechanically the most stable faeces, roughly twice as stable as those of small fish and three times more stable than faeces from large fish. The addition of 3 g kg,1 of guar gum saw some mechanical characteristics improve by about 700%. Faeces from large- and mid-sized fish were more easily stabilized than those of small fish. Mechanical recovery potential for faecal samples disrupted by water turbulence was determined. Stability differences observed for different fish size had no significant effect but the improvements imparted by guar gum reduced postfiltration effluent load to about 35% for large fish, about 24% for mid-size and about 22% for small fish. Faecal leaching decreased significantly with increasing stability. Guar gum was shown to have significant potential for improving the treatability of fish faecal waste. [source] Effect of dietary protein regime during the growing period on growth performance, feed utilization and whole-body chemical composition of Nile Tilapia, Oreochromis niloticus (L.)AQUACULTURE RESEARCH, Issue 13 2009Mohsen Abdel-Tawwab Abstract This study was conducted to evaluate the effect of various dietary protein regimes on growth performance, feed utilization and whole-body chemical composition of Nile tilapia, Oreochromis niloticus (L.). Twenty cages (1 m3 each) were randomly allocated to a four-replicate experiment to represent five treatments (T1,T5) where fish were randomly stocked at a rate of 50 fish (1.5,2.2 g) per cage. Fish in T1,T5 fed on a 45% crude protein (CP) diet for the first 4 weeks. In T1, T2 or T3 fish fed on 45%, 35% or 25% CP diets for the last 8 weeks respectively. In T4 fish fed 35% CP diet for the second 4 weeks followed by 25% CP diet for the last 4 weeks and in T5 fish fed 25% CP diet for the second 4 weeks followed by 35% CP diet for the last 4 weeks. Diets were offered to satiation and provided manually twice a day in the morning and in the afternoon, 6 days a week. The optimum fish growth and feed utilization were obtained at T1, T2 and T4. Protein efficient ratio and apparent protein utilization were lower at T1 and T2 than those of T3,T5. On the other hand, no significant changes in energy utilization were observed among the different treatments. There were no major changes in the carcass composition except in ash content, which was higher in T3 and T5 only. This study recommended that the dietary protein regime is an important management in tilapia culture, and the protein level could be reduced from 45% to 35% then to 25% on increasing the fish size. [source] Effect of temperature, stocking density and fish size on the ammonia excretion in palmetto bass (Morone saxatilis×M. chrysops)AQUACULTURE RESEARCH, Issue 4 2009Fu-Guang Liu Abstract Three temperature levels (18, 23 and 28 °C), three stocking density levels (0.72, 1.42 and 2.84 kg m,3) and two sizes of groups (averaging 104 and 173 g respectively) were used to conduct experiments on the effect of temperature, stocking density and fish size on the ammonia excretion (AE) of palmetto bass (Morone saxatilis×M. chrysops). The AE increased with the increase in temperatures by a significant degree (P<0.05) among different temperature groups. There appeared to be a tendency towards increase of the AE with increased stocking densities, and significant differences (P<0.05) were found among stocking groups. The AE of smaller size-group was significantly higher than that of the larger size-group. Diurnal variation of AE in palmetto bass showed that the AE rose greatly to reach a peak at about 4 h after feeding, and to the lowest values at about 24 h post feeding in all of the experimental groups. [source] A review of the biophysical properties of salmonid faeces: implications for aquaculture waste dispersal models and integrated multi-trophic aquacultureAQUACULTURE RESEARCH, Issue 3 2009G K Reid Abstract Knowledge of the quantitative and qualitative properties of salmonid faeces is necessary for aquaculture waste dispersal models, and the design of integrated multi-trophic aquaculture (IMTA) systems. The amount and proximate composition of salmonid faeces can be estimated using a mass-balance, nutritional approach. Indigestible components of salmonid diets have the potential to affect faecal ,cohesiveness' or ,stability'. Nutrient content and density of faeces can vary depending on diet and submersion time. Faecal density has a greater influence on settling velocity than faecal size. Published settling velocity data on salmonid faeces are highly variable due to differences in fish size, rearing systems, collection time, water density, methodology, the mass fraction tested and diet. Most faecal settling data used in published salmonid waste dispersal models are rudimentary and recent information suggests that such models are highly sensitive to this input. The design of open-water IMTA systems and estimation of nutrient capture and recovery from co-cultured filter feeders is difficult due to limited information on particle size, digestibility, settleable and non-settleable mass fractions of salmonid faeces at cage environments. Implications of faecal properties on the accountability for the effects of aquaculture nutrient loading are discussed. [source] | |||||||||||||