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1.
Abstract – The possibility to increase the proportion of migrating hatchery‐reared smolts by reducing their food ration was studied. Lake‐migrating, hatchery‐reared salmon (Salmo salar) and trout (Salmo trutta) smolts were either fed normal rations, based on recommendations from the fish‐farming industry, or reduced (15–20%) rations. They were released into the River Klarälven, western Sweden, and followed as they swam downstream to Lake Vänern, a distance of around 25 km. For both Atlantic salmon and brown trout, smolts fed a reduced ration migrated faster than fish fed a normal ration. Furthermore, a higher proportion of salmon smolts fed reduced rations migrated to the lake than fish fed normal rations in 2007 but not in 2006. This difference between years corresponded to greater treatment differences in size and smolt status in 2007 than in 2006. For trout, the proportion of migrating individuals and smolt development did not differ with ration size. Trout migrants fed a normal ration had a higher standard metabolic rate (SMR) than nonmigrants, whereas there was no difference in SMR between migrating and nonmigrating salmon. These results show that it is possible to use a reduced food ration to increase the migration speed of both Atlantic salmon and brown trout and to increase the proportion of migrating Atlantic salmon.  相似文献   

2.
Asian sea bass (Lates calcarifer) is one of the most important marine food fish species in Asia and Australia. To estimate the reproductive success of broodstock and heritabilities of growth‐related traits, two independent full‐factorial crosses (PI and PII) were created by crossing 10 males and 10 females. At 90 days post hatch (dph), the body weight (BW) and total length (TL) of 804 individuals from PI and 900 individuals from PII were measured and tissues samples of each fish were collected. Parents and offspring were genotyped with nine polymorphic microsatellites. Out of 1704 offspring from the two crosses, 98.7% were assigned to their parents. In PI, 19 of 20 parents produced offspring, while in PII, only five parents contributed to offspring. Low contribution of parents to offspring could lead to reduced genetic variation in the next generation. Heritabilities for growth‐related traits were estimated using the pedigrees reconstructed using microsatellite genotypes. The estimates of heritability were 0.22±0.16 and 0.25±0.18 for BW, 0.31±0.14 and 0.24±0.21 for TL and 0.22±0.22 and 0.15±0.09 for Fulton's condition factor in the two crosses respectively. Body weights at 90 dph and at harvest (289 dph) were significantly correlated (r=0.601, P<0.01). Therefore, growth‐related traits could be improved by exploiting additive genetic effects through selective breeding, and broodstock candidates could be selected early in the production cycle.  相似文献   

3.
Phenotypic plasticity is an important mechanism to maximise fitness in unpredictable environments by fine‐tuning phenotypes to a specific environmental setting. We used Nothobranchius furzeri, an African annual fish from temporary pools with erratic changes in habitat condition, to study changes in the allocation to growth and reproduction and to test the key trade‐off between egg size and number. In an experimental setting, we quantitatively varied ration at two levels and over two time periods, including temporal switches in ration level. As predicted, female N. furzeri possessed the capacity for compensatory growth, which surprisingly came with no longer‐term cost to fecundity. Females responded strongly to ration manipulation, with a pronounced decrease in fecundity associated with a low ration, even after accounting for body mass. Due to the unpredictability of offspring environment, we expected no adaptive change in oocyte size. However, females responded to the quality of their environment in accordance with an adaptive maternal effect, with females receiving a low ration producing larger eggs. Further, a switch in ration size in either direction was associated with a decrease in egg size. There was a trade‐off between egg size and number in half of the treatments, but high variability in egg size among females made the relationship complex. Overall, N. furzeri females demonstrated high plasticity in both growth rate and fecundity parameters. Females appear able to track and respond adaptively to unpredictable changes in food availability in their environment.  相似文献   

4.
Do disparate mechanisms determine growth rates of fish larvae in the different regions? The relationship between growth rates and environmental factors (sea temperature and food availability) was examined for larval Japanese anchovy Engraulis japonicus in geographically and environmentally different waters, through sagittal otolith microstructure analysis. Recent 3‐day mean growth rates directly before capture were positively related with sea‐surface temperature (SST) but not with food availability (plankton density) for the larvae in the Kuroshio Extension and Kuroshio–Oyashio transition regions of the western North Pacific. On the contrary, variations in recent growth rates were attributed to food availability (plankton density) as well as SST for the larvae in the East China Sea. In the shirasu fishing ground in Sagami Bay, larval growth rates were variable under the influences of both SST and food availability (feeding incidence). On the surface, the growth–environment relationships seemed to differ among regions. However, a definite general pattern of the dome‐shaped relationship between recent growth rates and SST was observed when all the regions were combined. Growth rates were similar even among clearly different regions if at the same SST. Overall, growth rates roughly increased with SST until they reached the maximum at SST of 21–22°C (i.e. optimal growth temperature), and declined when SST went over 21–22°C. On the contrary, no clear relationship was observed between growth rate and plankton density or between SST and plankton density. Therefore, the apparent among‐region differences would be firstly caused by the differences in regional SST range. The systematic mechanism of growth determination for widespread pelagic fish species larvae would be run by primarily sea temperature and secondarily food availability, at the species level.  相似文献   

5.
Species distribution models are commonly used to determine a species’ probability of occurrence but have not been used to examine the effect of environmental habitat suitability on fish condition, which is considered to be an integrated measure of physiological status. Here, we test for a relationship between oceanographic habitat suitability and the body condition of kingfish (Seriola lalandi) from eastern Australia. We (a) test whether individuals sampled from areas of high‐quality habitat were in better condition than individuals sampled from areas of low‐quality habitat, and (b) assess whether the condition of kingfish responded to oceanographic habitat suitability predicted at varying time‐before‐capture periods. Kingfish habitat was modelled as a function of sea surface temperature, sea‐level anomaly and eddy kinetic energy in a generalized additive modelling framework. Model predictions were made over one‐ to six‐week time‐before‐capture periods and compared to field‐derived kingfish condition data measured using bioelectrical impedance analysis. Oceanographic habitat suitability was significantly correlated with kingfish condition at time‐before‐capture periods ranging from one to four weeks and became increasingly correlated at shorter lead‐times. Our results highlight that (a) fish condition can respond sensitively to environmental variability and this response can be detected using oceanographic habitat suitability models, and (b) climate change may drive extensions in species range limits through spatial shifts in oceanographic habitat quality that allow individuals to persist beyond historical range boundaries without their body condition being compromised.  相似文献   

6.

The effects of fish size and nitrite level on metabolic rate and growth were investigated in the obligate air-breathing snakehead Channa striata, which is an important aquaculture species in Vietnam. Channa striata displayed respiratory size dependence, whereby the standard metabolic rate (SMR) and routine metabolic rate (RMR) decreased progressively in an exponential manner as fish size increased from 50 to 200 g. A mildly elevated nitrite level of 5% of the LC50 96 h (12 mg NO2?/L or safe concentration) induced significant increases in Channa striata SMR and RMR, which were almost double that of the control at the same size. At mild elevation, nitrite caused no significant effect on fish growth and survival during 3 months of rearing. However, both growth and survival rates of fish reared at severely elevated nitrite levels were significantly lower than those of the control; in particular, survival rates were under 50%. While changes in size reduced SMR and RMR, the percentage of air oxygen partitioning remained unchanged. Channa striata upregulation of SMR and RMR and air-breathing regulation were not significantly proven in this study. In summary, maintaining water environments at levels lower than 12 mg NO2?/L with ample oxygenation will not affect the growth and survival rate of snakeheads.

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7.
Abstract – There is substantial need for models that accurately predict habitat selection by fishes for purposes ranging from the elaboration of ecological theory to the preservation of biodiversity. We have developed a new and highly tractable optimal foraging model for drift‐feeding fishes that is based on the profitability of occupying varying focal‐point velocities in a stream. The basic model can be written as: Ix = (Ex * Px) = {(D * A * V) * [1/(1 + e(b + cV))]} ? Sx, where: (1) Ix is the net energy intake at velocity x; (2) E is prey encounter rate; (3) P is prey capture success rate which can be modelled as 1/(1 + e(b + cV)) where b and c are fitting constants from the prey capture success curve; (4) D is the energy content of prey (J/m3) in the drift; (5) A is the visual reactive area of the fish; (6) V is velocity (cm/s); and (7) S is the cost of maintaining position (J/s). Given that D, A and S can be considered constant over the range of velocities occupied by these fishes, the model reduces to e(b + cV) = 1/(cV ? 1) which we solved iteratively to yield an optimal focal‐point velocity for species in each sample. We tested the model by comparing its predictions to the mean focal‐point velocities (i.e. microhabitats) occupied by four species of drift‐feeding minnows in two sites in a stream in North Carolina, USA. The model successfully predicted focal‐point velocities occupied by these species (11 out of 14 cases) in three seasonal samples collected over 2 years at two sites. The unsuccessful predictions still were within 2 cm/s of the 95% confidence intervals of mean velocities occupied by fishes, whereas the overall mean deviation between optimal velocities and mean fish velocities was small (range = 0.9 and 3.3 cm/s for the warpaint shiner and the Tennessee shiner, respectively). Available focal‐point velocities ranged from 0–76 to 0–128 cm/s depending on site and season. Our findings represent one of the more rigorous field tests of an optimal foraging/habitat selection model for aquatic organisms because they encompass multiple species and years, and for one species, multiple sites. Because of the ease of parameterization of our model, it should be readily testable in a range of lotic habitats. If validated in other systems, the model should provide critical habitat information that will aid in the management of riverine systems and improve the performance of a variety of currently used management models (e.g. instream flow incremental methodology (IFIM) and total maximum daily load calculations (TMDL)).  相似文献   

8.
  • 1. Habitat suitability criteria that fail to incorporate temporal variability in habitat preferences of stream fish may mis‐represent critical habitat requirements and lead to setting of inappropriate flow targets when used in instream flow assessments. Developing suitability criteria from daytime observations alone relies on the assumption that habitat preferences are constant over the diel cycle. Few studies have tested these assumptions, particularly for small‐bodied, cryptic, benthic species.
  • 2. During summer in two gravel‐bed rivers, bluegill bullies (Gobiomorphus hubbsi), torrentfish (Cheimarrichthys fosteri) and upland bullies (Gobiomorphus breviceps) exhibited strong preferences with respect to water depth, velocity and substratum size. All three species underwent a diel shift in microhabitat preference for at least two of these variables.
  • 3. Microhabitat preferences were generally weaker when fish were active at night; bluegill bullies, upland bullies and especially torrentfish were observed over a broader range of depths, velocities and substratum sizes at night than during the day. Observations of fish in a stream simulator confirmed that bluegill bullies and torrentfish showed a preference for runs at dusk and return to riffles before dawn, but habitat preferences of upland bullies remained static across the diel cycle.
  • 4. Diel microhabitat shifts affected the assessment of flow requirements. Instream habitat analysis of the Waipara River using separate day and night suitability criteria predicted differing amounts of habitat available at a given flow, and the relationships between fish abundance, fish density and flow. The presence of diel microhabitat shifts in stream fishes suggests that instream habitat analyses will produce more effective and defensible flow recommendations when patterns of nocturnal microhabitat preferences are known and critical habitat bottlenecks can be identified. Copyright © 2011 John Wiley & Sons, Ltd.
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9.
  1. Removal of instream woody habitat (IWH) is one factor attributed to declines in fish populations worldwide. Restoration of IWH to help fish populations recover is now common; however, quantitative predictions about the outcomes of these interventions is rare. As such, quantitative links between IWH and fish abundance is of interest to managers to inform conservation and restoration activities.
  2. Links between instream habitat attributes, especially IWH, and selected fish species of recreational, cultural, and ecological significance were explored at 335 sites spanning eight streams across south‐eastern Australia. Data were collected on fish abundance and length, IWH density and a range of other habitat attributes at a scale that incorporated at least one of each of the major mesohabitat types (functional river elements). The data were analysed using Bayesian hierarchical generalized linear mixed models to examine fish habitat associations and used to make quantitative predictions of responses to future restoration.
  3. Strong positive relationships were found between fish abundance and IWH density and the strength of this relationship varied between species and waterways. Murray cod (Maccullochella peelii), a species commonly targeted by IWH interventions, displayed the strongest association with IWH density. River blackfish (Gadopsis marmoratus) also showed a significant relationship with IWH, but this effect was waterway specific. Fish length was only related to IWH for river blackfish. These results may reflect differences in the life histories of these two species. We suggest that differences in habitat association through ontogeny may be more relevant at smaller spatial scales.
  4. The results generated in this study can be used to guide waterway restoration and develop quantitative predictions about how fish might respond to IWH interventions across south‐eastern Australia. This approach provides a powerful quantitative framework within which to explore management options and objectives, and to test our predicted responses to habitat restoration.
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10.
The main hypothesis of this study was that if stomach volume is correlated with food intake it can be estimated without laborious and destructive direct measurement. Rainbow trout, Oncorhynchus mykiss (Walbaum), ca. 500–1300 g, were starved for 1, 4, 8 or 16 days at 15°C after which they were fed in excess with dry pellets containing known amounts of X‐ray‐dense markers. Immediately after feeding the fish were killed, X rayed and weighed. Then the stomach was dissected, its contents removed and weighed, and stomach volume was measured. X‐ray plates were developed and feed intake was estimated based on the amount of marker. All measured variables correlated positively with stomach volume. The best fit for linear regression models was obtained for fish starved for 4 days, where stomach content (dry mass) explained 94%, food intake (based on X‐ray measurement) 77% and fish mass 62% of the variation in stomach volume. However, as stomach content measurement can be a lethal, or at least very stressful, event for the fish, the accuracy of food intake measurement (X‐ray) could be increased using multiple regression. In multiple linear regressions, R2‐values varied between 0.79 (16‐day starvation) and 0.91 (1‐day starvation) with food intake and fish mass as explanatory variables for stomach volume. These results indicate that the stomach volume in rainbow trout can be estimated satisfactorily using indirect methods, which are not detrimental to the fish, although feeding history may affect the accuracy of the estimates.  相似文献   

11.
Across taxa, it is generally accepted that there are fitness advantages to rapid growth early in life. For stream‐dwelling salmonids, however, high temperatures and associated energetic costs during the summer growing season might offset or even prevent the competitive advantage of large body size. Our overall objective was to understand the relative importance of factors that can cause variation in growth rates in an age‐0 cohort of wild steelhead (Oncorhynchus mykiss) in Idaho, USA, where temperatures approach, and temporarily exceed, their tolerance level. For individually tagged fish inhabiting the same stream reach, we found that growth rates were negatively related to fish mass (slopes of the two best approximating models were both ?0.024). Comparing growth rates from 16 different stream reaches throughout the watershed, we found that temperature‐induced metabolic cost was the single best approximating model (AIC wi = 1.0) of the variation in individual growth rates. The bioenergetic model showed that mass‐specific metabolic costs decreased with mass, but the absolute energetic demands increased over the same size range. Because temperature had a multiplicative effect on metabolic cost, our results suggest that the effect of food limitation increased with fish size. We conclude that high water temperatures pose energetic bottlenecks and can be a potentially strong mechanism limiting growth in juvenile salmonids in summer, particularly as streams in the region experience warming trends.  相似文献   

12.
The effect of stocking density on feed intake, feed utilization and feeding behaviour was studied in groups of rainbow trout submitted to different levels of food accessibility. In the first experiment, 18 groups of 100, 300 or 500 fish (initial individual weight 26 ± 0.5 g) were held in 1 m3 tanks where they were fed: in excess using belt feeders; or by means of self‐feeders with a fixed reward level (4 g per trigger actuation); or a reward level proportional to fish density (2 g/100 fish/trigger actuation). Final biomass after 125 days was c. 25, 70 and 100 kg/m3 in groups of 100, 300 and 500 fish respectively. Growth and feed intake was affected by fish density, feeding technique and reward level. However, feed efficiency, body composition, as well as nutrient retention and loss were unaffected by the treatment. In the self‐fed groups, daily pattern of feeding activity was affected by fish density when the reward level was fixed but not when the reward level was proportional to fish density. In a second experiment, groups of 100 or 500 fish (same initial individual weight) had access to one or three self‐feeders. Access to multiple self‐feeders had no positive effect on any of the studied parameters. The fish used only one of the three feeders at a time, and the three feeders where not used equally. We conclude that feed intake but not feed utilization was impaired by increased density, indicating that density in itself is not stressful to the fish. Food accessibility is the main factor responsible for the observed density – related decrease in growth.  相似文献   

13.
Abstract – Social and foraging modes in fish often vary between individuals with different body sizes and between populations under different ecological conditions. We studied social and foraging behaviour of algae‐grazing fish Plecoglossus altivelis ryukyuensis (Ryukyu‐ayu) inhabiting Japanese subtropical island streams. Ryukyu‐ayu exhibited four behavioural modes: territorial, schooling, solitary and floating. Their body sizes differed among these modes. Territorial fish predominantly foraged on benthic algae, whereas schooling and solitary individuals frequently consumed drifting materials as well. Schooling fish were smaller than territorial fish, but, unlike some other algae‐grazing fish species, did not use schooling to gain access to food within territories. Territorial fish attacked smaller conspecifics but exhibited lateral display towards larger fish and schooling fish while occasionally attacking grazing gobies. Larger fish maintained larger feeding territories and occupied territories for longer periods than smaller fish did. This suggests that, in Ryukyu‐ayu, intra‐ and interspecific food competitions and relative body size can influence diverse behavioural modes and duration of territory occupation. We also found that Ryukyu‐ayu foraged more often and had larger feeding territories than ayu P. a. altivelis inhabiting temperate streams. We conclude that foraging strategies of Ryukyu‐ayu may have adapted to subtropical island streams, where algal productivity is much lower than that in temperate regions.  相似文献   

14.
This experiment was conducted to determine the optimum dietary protein level for juvenile olive flounder Paralichthys olivaceus (Temminck et Schlegel) fed a white fish meal and casein‐based diets for 8 weeks. Olive flounder with an initial body weight of 4.1 ± 0.02 g (mean ± SD) were fed one of the six isocaloric diets containing 35%, 45%, 50%, 55% and 65% crude protein (CP) at a feeding rate of 4–5% of wet body weight on a dry‐matter basis to triplicate groups of 20 fish per aquarium. After 8 weeks of feeding, per cent weight gain (WG) and feed efficiency ratios of fish fed the 55% CP diet were not significantly higher than those from fish fed the 50% and 65% CP diets, but significantly higher than those from fish fed the 35% and 45% CP diets. Fish fed the 50%, 55% and 65% CP diets had significant higher specific growth rates than did fish fed the 35% and 45% CP diets; however, there was no significant difference among fish fed the 50%, 55% and 65% CP diets. The protein efficiency ratio was inversely related to the dietary protein level; that is, maximum efficiency occurred at the lowest dietary protein level. Broken‐line model analysis indicated that the optimum dietary protein level was 51.2 ± 1.8% for maximum weight gain in juvenile olive flounder. The second‐order polynomial regression analysis showed that the maximum WG occurred at 57.7% and it revealed that the minimum range of protein requirement was between 44.2% and 46.4%. These findings suggest that the optimum dietary protein level for maximum growth could be greater than 46.4%, but less than 51.2% CP in fish meal and casein‐based diets containing 17.0 kJ g?1 energy for juvenile olive flounder.  相似文献   

15.
Abstract – Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life‐history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life‐history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3–5 sea‐winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life‐history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life‐history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world‐wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near‐shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near‐shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour.  相似文献   

16.
Florida pompano has been identified as a promising candidate for commercial‐scale aquaculture production, but to date, little information is available regarding captive broodstock spawning characteristics. Genetic markers were tested for their power in monitoring mating outcomes and potential in analysing heritability of rapid growth trait in Trachinotus carolinus. A total of 20 unrelated adults (10 females and 10 males) were chosen for a hormone‐induced mass spawning event. The 515 fastest growing and 485 slowest growing fish of the total 4852 offspring were considered a selected progeny stock, and fish were collected at 45 days post hatch based on their growth traits. Parentage analyses based on the 20 breeders and 1,000 selected progeny were performed using a total of nine microsatellite markers, a 100% assignment rate was achieved, and a four‐marker set was the minimum number for the parentage assignment. The effective breeding number for the selected progeny was 11 (six females and five males), among which three females and two males were predominant contributors with the total contribution of 95.8% and 94.7% respectively. The proportion of fast‐growing offspring from broodfish and each mating cross (sire/dam) was used for detecting whether variation in growth of the offspring was related to parental stocks. Results showed that three adults and their mated combination exhibited the greatest fast‐growing offspring proportion (69.73% and 55.95%). This research provided new information regarding spawning performance and parental contribution during mass spawning events; both important first steps towards developing improved management strategies for captive Florida pompano broodstock.  相似文献   

17.
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18.
The effect of social stress, induced by confinement in pairs, on the SMR of the brown trout, Salmo trutta (L.), was investigated. Fish were confined in pairs under laboratory conditions and allowed to establish social hierarchies, with one fish becoming dominant and the other subordinate. The change in SMR of the subordinate fish was significantly greater than that of their respective dominant. Also, the more aggressive the dominant behaved towards the subordinate with which it was paired, the greater the increase in the SMR of the subordinate fish appeared to be. It is concluded that social stress causes an increase in SMR in subordinate fish and therefore imposes a metabolic disadvantage.  相似文献   

19.
Understanding trade-offs associated with occupying various aquatic habitats provides a mechanistic understanding of habitat needs that can be used to evaluate the consequences of habitat loss or alteration. We used instream enclosures and field observations to identify how velocity affects the growth rates of four native species in the upper Gila River basin: longfin dace (Agosia chrysogaster) and speckled dace (Rhinichthys osculus), two species of no conservation concern, and loach minnow (Tiaroga cobitis) and spikedace (Meda fulgida), two federally endangered species. Elevated velocity was predicted to increase food delivery through drift or stimulation of benthic primary production. Energetic costs of high-velocity habitat were predicted to vary with morphology and behaviour and be lowest for speckled dace and loach minnow because they are adapted to occupy interstitial spaces of the substrate in riffles. Spikedace and longfin dace should perform best in moderate velocities, where the trade-off between exposure to drifting macroinvertebrates outweighs the energetic costs of maintaining position in the water column. Growth rates of loach minnow and speckled dace increased in higher velocities, but contrary to our initial predictions, spikedace growth rates also increased in high-velocity habitats while longfin dace grew fastest in low-velocity habitats; similar to the locations these species occupied based on field observations. These results indicate that for spikedace, the increased abundance of drifting macroinvetebrates in high-velocity habitats outweighs the energy expenditure, but for longfin dace the energetic costs of occupying moderate to high-velocity habitats outweigh the benefit to increased food availability. Our experiment provides a mechanistic understanding of habitat requirements across species and may inform predictions on how modifications or restoration of riverine ecosystems influence native fish diversity.  相似文献   

20.
Entrainment and impingement of two non‐salmonid species susceptible to entrainment at irrigation diversions, silver perch, Bidyanus bidyanus (Mitchell), and golden perch, Macquaria ambigua (Richardson), were examined at an experimental intake screen in a laboratory flume under a range of velocities and light levels. The presence of an intake screen significantly reduced entrainment, in some cases reducing mortality from over 90% (unscreened) to less than 2% (when screened). Although some differences in behaviour existed between species, approach velocities (measured 8 cm in front of the screen) up to 0.4 m s?1 effectively reduced entrainment, with very little injury or mortality resulting from incidental screen contacts or impingement. Both species used visual cues to negotiate the screen face, thereby increasing their ability to avoid contact at higher velocities. In the absence of these visual cues, positive rheotactic behaviour was enhanced and fish mostly avoided approaching the screen. These results demonstrate that fish screens operated at approach velocities of up to 0.4 m s?1 have great potential for the protection of silver perch and golden perch juveniles at irrigation intakes.  相似文献   

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