Feeding by marine fish larvae: developmental and functional responses

Synopsis The relationship between prey consumption rate and prey concentration (functional response), and its change with growth (developmental response) were examined in the laboratory for three species of marine fish larvae: bay anchovy Anchoa mitchilli (Engraulidae), sea bream Archosargus rhomboidalis (Sparidae) and lined sole Achirus lineatus (Soleidae). The major objective was to determine relative predatory abilities of the larvae by fitting feeding rate data to developmental and functional response models. Feeding success, prey capture success, attack rates, handling times and search rates were estimated. Prey consumption rates and attack rates of bay anchovy usually were highest, but at the lowest prey level (50 per liter) first-feeding sea bream larvae had the highest consumption rate. Sea bream could consume prey at near-maximum rates at prey levels lower than those required by the other species. As larvae grew, time searching per attack decreased rapidly for all species, especially at low prey levels. Handling time also decreased, but most rapidly for bay anchovy. Search rates were highest for bay anchovy and lowest for lined sole. Bay anchovy had the best apparent predation ability, but when previous results on larval growth rates, survival rates and growth efficiencies were considered, sea bream larvae were the most efficient predators and the least likely of the three species to be limited by low prey levels.     

A model for growth of Artemia franciscana cultures based on food ration-dependent gross growth efficiencies

Laboratory cultures of Artemia franciscana grown under batch regimes at constant temperatures (28 °C) and salinity (35 g l^–1), three initial food concentrations (0.1, 0.4 and 1 M cells ml^–1), various daily food rations (0.1–9M Dunaliella tertiolecta cells Artemia ^–1), and different population densities (1–16 ind ml^–1) were used to develop a model of population growth. Growth rates and gross growth efficiencies (K ₁) were largely independent of population densities and initial food concentrations but determined by age and daily amount of food ingested. While maximum growth rates were found with the highest rations, K _{1 max} peaked at rations of 0.5 million cells d^–1 and decreased at feeding levels above this. A contour plot showing the trend relating K ₁ to Artemia size and ingestion rate in combination and was used to model growth in analogous controlled feeding conditions. Computer simulations using this model paralleled published results of final 15-day average individual sizes of Artemia. Optimal results for near constant food utilization are predicted for high initial population densities (100 Artemia nauplii ml ^–1) and daily culls of enough animals to equilibrate food demand with food availability. This strategy could permit a range of Artemia sizes harvested, maximize final individual sizes and retain high total yields (> 1.2 kg dry wt 1^–1). Effects of different culture strategies are discussed.     

Effects of satiation on feeding and swimming behaviour of planktivores

Hunger affects the feeding and swimming behaviour in fish. After 36 h of food deprivation, the feeding and swimming behaviour of Pseudorasbora parva (Cyprinidae) was studied under different prey densities (0.5, 1, 2, 5, 10 and 25 of Daphnia pulex per liter). The initial feeding rates showed marked variations in relation to prey availability. Under high prey densities, the initial feeding rate of fish was higher and subsequently decreased faster, when compared to those feeding under low prey densities. At higher prey densities, two factors were involved: that of higher prey encounter rates and also the attainment of food satiation at a faster rate. Across all prey densities, the feeding rates of fish reached a plateau after satiation. The swimming speed of fish was found to be negatively related to the prey density and a significant change in swimming speed was noted as being directly related to the level of satiation. It was found that the increasing satiation level greatly influenced the handling time and reactive volume of predator, which finally caused reduced feeding rates.     

Fruit diet of Alouatta guariba and Brachyteles arachnoides in Southeastern Brazil: comparison of fruit type, color, and seed size

Fruit is an important food resource for neotropical primates. In this study I compare the fruit diet of sympatric brown howlers (Alouatta guariba) and southern muriquis (Brachyteles arachnoides). Feeding behavior was studied over 12 months and fruit species consumed were identified and assigned to the categories fruit type, fruit color, and seed size. Observed-fruit feeding records were compared with expected records determined from local availability of the fruit of the tree species. I also determined dietary overlap. Fruit consumption occupied 8 and 12% of the feeding time of A. guariba and B. arachnoides, respectively. Fruit from eight tree species were consumed by the former and fruit from twenty-two species by the latter. Patterns of fruit selection of A. guariba and B. arachnoides varied widely. Although howlers and muriquis converge behaviorally by selecting fruit with common attributes (fleshy/unprotected, violet and brown/black-colored), unlike A. guariba, B. arachnoides fed on immature seeds of fleshy/protected and dry fruit. Large seeds were ingested, and defecated intact, by B. arachnoides only. There was little overlap of fruit diet even within categories that had been selected by both, suggesting that dietary divergence is occurring at the interspecific level. Different resource exploitation probably mediates the coexistence of A. guariba and B. arachnoides in low diversity, semideciduous forests, where the environment imposes narrow limits on primate food choices.     

Effects of food limitation and temperature on cladocerans from a tropical Brazilian lake

Food limitation was tested in the laboratory by individual growth and reproduction of two cladoceran species, Ceriodaphnia richardi and Daphnia gessneri, from the shallow tropical Brazilian Lake Monte Alegre. The cladocerans were fed cultivated green alga Scenedesmus spinosus in concentrations of 0.20, 0.10, 0.05, and 0.025 mg C l⁻¹. Higher biomass and growth rates occurred in the two highest-food concentrations; the two lowest ones negatively affected clutch size and first reproduction. The threshold food concentration is lower than 0.025 mg C l⁻¹ and the incipient limiting level is a value between 0.10 and 0.20 mg C l⁻¹. The largest species, D. gessneri, was more sensitive to low food concentrations. The effects of low and high temperatures (19 and 27°C) were evaluated by life table experiments with three cladocerans from the lake—Daphnia ambigua, D. gessneri, and Moina micrura—with no food limitation (1 mg C l⁻¹ of S. spinosus). Higher population growth rates for the three species were found at 27°C; better performance in most life table parameters was observed for the former two species at the highest temperature, D. gessneri being the most sensitive to the lowest temperature. There are indications that temperature is an important abiotic factor that constrains populations of cladocerans for a short period in winter in the lake, when temperature decreases to 18–19°C. However, its influence cannot be separated from a biotic factor such as food, whose effect is stronger in the cool season, when concentrations are lower and contribution of inedible algae is relatively higher.     

Food consumption of five deep‐sea fishes in the Balearic Basin (western Mediterranean Sea): are there daily feeding rhythms in fishes living below 1000 m?

Predation and food consumption of five deep‐sea fish species living below 1000 m depth in the western Mediterranean Sea were analysed to identify the feeding patterns and food requirements of a deep‐sea fish assemblage. A feeding rhythm was observed for Risso's smooth‐head Alepocephalus rostratus, Mediterranean grenadier Coryphaenoides mediterraeus and Mediterranean codling Lepidion lepidion. Differences in the patterns of the prey consumed suggest that feeding rhythms at such depths are linked with prey availability. The diets of those predators with feeding rhythms are based principally on active‐swimmer prey, including pelagic prey known to perform vertical migrations. The diets of Günther's grenadier Coryphaenoides guentheri and smallmouth spiny eel Polyacanthonotus rissoanus, which did not show any rhythm in their feeding patterns, are based mainly on benthic prey. Food consumption estimates were low (<1% of body wet mass day^?1). Pelagic feeding species showing diel feeding rhythms consumed more food than benthic feeding species with no feeding rhythms.     

Amino acid consumption by Chloroflexus aurantiacus in batch and continuous cultures

Amino acid consumption was studied with batch and continuous chemostat cultures of Chloroflexus aurantiacus grown phototrophically in complex medium with casamino acids (Pierson and Castenholz 1974). Amino acids like Arg, Asx, Thr, Ala, Tyr, which were utilized during the early exponential phase by cells grown in batch cultures were consumed in chemostat cultures essentially at any of the dilution rates employed (0.018–0.104 h^-1). Those amino acids which were taken up during subsequent phases of growth were consumed in chemostat cultures preferentially at low dilution rates. For example, the consumption of Glx was enhanced during the late exponential phase and at low dilution rates. At high dilution rates Glx was not consumed at all. Since Glx utilization largely paralleled bacteriochlorophyll formation, it is discussed that formation of the photopigment depends on the intracellular availability of Glu as the exclusive precursor for tetrapyrrole synthesis.     

The energetics of starvation and growth after refeeding in juveniles of three cyprinid species

Synopsis Experiments were conducted to monitor changes in body mass and metabolic energy expenditure before, during, and after periods of starvation in juveniles of three species of cyprinids: Leuciscus cephalus, Chalcalburnus chalcoides mento, and Scardinius erythrophthalmus. During the starvation period all fish lost weight at about the same rate and the total amount of oxygen consumed during an experimental period of 20 h was about 40% lower in the starved than in the fed groups. Upon refeeding, both mass specific maintenance; and routine rates of metabolism as well as relative growth rates increased rapidly, the peaks of these increases being directly proportional to the length of the starvation period. Maximum compensatory growth was observed after four weeks of starvation in C. chalcoides and S. erythrophthalmus, with relative growth rates reaching 30% d^-1 during the first measuring interval after refeeding. The pattern of time-dependent compensatory growth displayed by these fish is similar to the responses of a colonial hydroid in which the rate of catch-up growth increased with the amount of stress to which the animals had been exposed. The exact cost of compensatory growth cannot be calculated because oxygen consumption and growth were not measured simultaneously. However, on the basis of data and calculations reported by Wieser & Medgyesy (1990) it appears that compensatory growth, if fuelled by the metabolic power indicated by our measurements of oxygen consumption, would have to be about twice as efficient as normal growth in the related species Rutilus rutilus.     

Food and growth relations of the marine microzooplankter,Synchaeta cecilia (Rotifera)

The trophic interactions of the marine rotifer Synchaeta cecilia were investigated by determining its feeding and growth rates on a wide variety of marine phytoplankton and by determining its susceptibility to predation by the calanoid copepod, Acartia tonsa. Reproduction of S. cecilia was sustained in four-day feeding trails by 13 of 37 algal species tested. Growth-supporting species included species of Cryptophyceae, Dinophyceae, Chlorophyceae and Haptophyceae in sizes from 4 to 47 μm. Within these taxa, other species in the acceptable size range failed to support growth. No species of Cyanophyceae, Bacillariophyceae, or Chrysophyceae supported growth of the rotifer. S. cecilia can be maintained on unialgal cultures of Cryptophyceae but growth is enhanced by a combination of two or three species; a mixture of Chroomonas salina (Cryptophyceae), Heterocapsa pygmaea (Dinophyceae), and Isochrysis galbana (Haptophyceae) has sustained laboratory stocks of S. cecilia for over four years. The expected response of S. cecilia to food quantity was observed: as food concentration was increased from 58 to 1154 μg C 1⁻¹, the population growth constant increased from 0.17 to 0.60 d⁻¹ at 20°C. This is equivalent to population doubling times of 4.0 and 1.1 days at H. pygmaea densities of 500 and 10⁴ cells ml⁻¹, respectively. The susceptibility of S. cecilia to predation was investigated by determining its rate of capture by the omnivorous marine copepod Acartia tonsa. At prey densities of 5 to 35 μg C 1⁻¹ (0.3 to 1.9 individuals 1⁻¹), A. tonsa readily ingested S. cecilia at rates up to 3 μg C copepod⁻¹ day⁻¹.     

The ecology of newt tadpoles

Food consumption of newt tadpoles caught during July and August was estimated as C=34W^1·11±0·12 where C is food consumption in milligrams wet weight/day and W is the live weight in grams. Well-fed tadpoles assimilated the food with an efficiency of 90–6%, but at low rates of feeding, the efficiency fell. Gross growth efficiency was about 35 % at maximum rations.     

Feeding preferences and grazing rates of Pfiesteria piscicida and a cryptoperidiniopsoid preying on fish blood cells and algal prey

The grazing rates and feeding preferences of the dinoflagellates Pfiesteria piscicida and a cryptoperidiniopsoid on the alga Rhodomonas sp. and fish blood cells were calculated at different ratios of the two food types and at different total food densities. Data from 6 h grazing periods within microcosms were used to calculate grazing rates. Grazing rates of both dinoflagellates increased linearly with an increased ratio of blood cells to Rhodomonas, and P. piscicida had a higher maximum grazing rate than the cryptoperidiniopsoid. The grazing rate of P. piscicida on Rhodomonas also increased with increased Rhodomonas densities relative to the blood cells, but increased densities of Rhodomonas did not increase the grazing rate of the cryptoperidiniopsoid, suggesting a lower feeding threshold for this species. Both dinoflagellates demonstrated a preference for fish blood cells over Rhodomonas cells, with no significant difference in the index of preference between the two species. Total food abundance affected the degree of preference differently for each dinoflagellate species. A higher index of feeding preference was attained by P. piscicida when resource levels were high, while the cryptoperidiniopsoid did not show this response. A preference for fish blood cells occurred at all food ratios for both dinoflagellates, including when blood cells were scarce relative to the alternate food type (15% of total available food). These results suggest that these strains of P. piscicida and the cryptoperidiniopsoid share similar feeding preferences for the prey types tested, although cryptoperidiniopsoids have not been associated with fish kills.     

Bioefficacy and mode-of-action of some limonoids of salannin group fromAzadirachta indica A. Juss and their role in a multicomponent system against lepidopteran larvae

Biological activities of the salannin type of limonoids isolated fromAzadirachta indica A. Juss were assessed using the gram pod borerHelicoverpa armigera (Hubner) and the tobacco armywormSpodoptera litura (Fabricius) (Lepidoptera: Noctuidae). Inhibition of larval growth was concomitant with reduced feeding by neonate and third instar larvae. All three compounds exhibited strong antifeedant activity in a choice leaf disc bioassay with 2.0, 2.3 and 2.8 (μ/cm² of 3-O-acetyl salannol, salannol and salannin, respectively deterring feeding by 50% inS. litura larvae. In nutritional assays, all three comounds reduced growth and consumption when fed to larvae without any effect on efficiency of conversion of ingested food (ECI), suggesting antifeedant activity alone. No toxicity was observed nor was there any significant affect on nutritional indices following topical application, further suggesting specific action as feeding deterrents. When relative growth rates were plotted against relative consumption rates, growth efficiency of theH. armigera fed diet containing 3-O-acetyl salannol, salannol or salannin did not differ from that of starved control larvae (used as calibration curve), further confirming the specific antifeedant action of salannin type of limonoids. Where the three compounds were co-administered, no enhancement in activity was observed. Non-azadirachtin limonoids having structural similarities and explicitly similar modes of action, like feeding deterrence in the present case, have no potentiating effect in any combination.     

Effect of ration size and feeding frequency on growth, size distribution and survival of juvenile clownfish, Amphiprion percula

This study describes the growth of juvenile clownfish, Amphiprion percula Lacépède 1802, fed with an artificial diet at six ration sizes of 2, 4, 6, 8, 10 and 12% of body mass per day (BM day^?1) each at a feeding frequency of once, twice and three times per day. The effect of ration size on growth depended on the feeding frequency. In fish fed once a day growth did not improve above a ration size of 8% BM day^?1. At two feedings per day fish required a ration size of at least 6% BM day^?1 to achieve good growth, and fish fed three times per day grew at similar rates above a ration size of 4% BM day^?1. A model to estimate the combined effect of ration size and feeding frequency is presented. The results lead to the suggestion of a simple length‐based feeding regimen that could be tested in future studies on this species or adapted for use in other species.     

Rotifers as food in aquaculture

The rotifer Brachionus plicatilis (O.F. Muller) can be mass cultivated in large quantities and is an important live feed in aquaculture. This rotifer is commonly offered to larvae during the first 7–30 days of exogenous feeding. Variation in prey density affects larval fish feeding rates, rations, activity, evacuation time, growth rates and growth efficiencies. B. plicatilis can be supplied at the food concentrations required for meeting larval metabolic demands and yielding high survival rates. Live food may enhance the digestive processes of larval predators. A large range of genetically distinct B. plicatilis strains with a wide range of body size permit larval rearing of many fish species. Larvae are first fed on a small strain of rotifers, and as larvae increase in size, a larger strain of rotifers is introduced. Rotifers are regarded as living food capsules for transferring nutrients to fish larvae. These nutrients include highly unsaturated fatty acids (mainly 20: 5 n–3 and 22: 6 n–3) essential for survival of marine fish larvae. In addition, rotifers treated with antibiotics may promote higher survival rates. The possibility of preserving live rotifers at low temperatures or through their resting eggs has been investigated.     

Biofiltering efficiency in removal of dissolved nutrients by three species of estuarine macroalgae cultivated with sea bass (Dicentrarchus labrax) waste waters 1. Phosphate

The potential of three estuarine macroalgae (Ulvarotundata, Enteromorpa intestinalis andGracilaria gracilis) as biofilters for phosphate ineffluents of a sea bass (Dicentrarchus labrax) cultivationtank was studied. These seaweeds thrive in Cádiz Bay and were alsoselected because of their economic potential, so that environmental andeconomicadvantages may be achieved by future integrated aquaculture practices in thelocal fish farms. The study was designed to investigate the functioning of Pnutrition of the selected species. Maximum velocity of phosphate uptake (2.86mol PO₄ g^–1 dry wth^–1) was found in U. rotundata.This species also showed the highest affinity for this nutrient. At low flowrates (< 2 volumes d^–1), the three species efficientlyfiltered the phosphate dissolved in the waste water, with a minimum efficiencyof 60.7% in U. rotundata. Net phosphate uptake rate wassignificantly affected by the water flow, being greatest at the highest rateassayed (2 volumes d^–1). The marked decrease in tissue P shownby the three species during a flow-through experiment suggested that growth wasP limited. However, due to the increase in biomass, total P biomass increasedinthe cultures. A significant correlation was found between growth rates and thenet P biomass gained in the cultures. A three-stage design under low water flow(0.5 volumes d^–1) showed that the highest growth rates (up to0.14 d^–1) and integrated phosphate uptake rates(up to 5.8 mol PO₄ ^3– g^–1dry wt d^–1) were found in E.intestinalis in the first stage, with decreasing rates in thefollowing ones. As a result, phosphate become limiting and low increments oreven losses of total P biomass in these stages were found suggesting thatphosphate was excreted from the algae. The results show the potential abilityofthe three species to reduce substantially, at low water flow, the phosphateconcentration in waste waters from a D. labrax cultivationtank, and thus the quality of effluents from intensive aquaculture practices.     

Growth, survival, and starvation resistance of Colorado squawfish larvae

Synopsis Growth and survival of Colorado squawfish, Ptychocheilus lucius, larvae under fluctuating 18, 22, and 26° C (5° C diel fluctuations) and constant 18, 22, 26° C, and 30° C temperature conditions and ration size corresponding to 12.5, 28,64,142, 320 brine shrimp nauplii fish^–1 day^–1 determined from laboratory experiments. Growth was optimal at 31° C and high at temperatures of 26° C to 30° C, at the highest food abundance. Lowest growth was under lowest food rations and highest temperatures. Growth of Colorado squawfish larvae declined substantially at temperatures < 22° C. Neither growth nor survival was significantly different between fluctuating or constant regimes. Survival of Colorado squawfish larvae was highest (95%) at 26.2° C and 235 nauplii fish^–1 day^–1 and high at temperatures of 20 to 30° C with food abundance > 180 nauplii fish^–1 day^–1. Survival was lowest when food abundance was low and temperature was high. Highest mortality occurred more than 20 days after experiments began and mortalities occurred sooner in higher than lower temperatures. Colorado squawfish larvae denied food for 5, 10, or 15 d after first feeding could have begun (6 d), had survival greater than 87 % which was equivalent to continuously fed controls. Survival of fish denied food for 17.5 d after feeding could have begun declined from 84% before feeding to 57% after feeding. Point of no return was estimated between 17.5 and 20 d. Colorado squawfish have relatively high starvation resistance. Low, stable flows that simulate natural hydrographs may enhance growth, survival, and recruitment of early life stages of Colorado squawfish by increasing water temperature and food abundance in regulated rivers of the Colorado River basin.     

Combined Effects of Food Concentration and Temperature on Competition Among Four Species of <Emphasis Type="Italic">Brachionus </Emphasis>(Rotifera)

We evaluated the effect of algal food density (1.5 × 10⁶, 3.0 × 10⁶ and 4.5 × 10⁶ cells ml⁻¹ of Chlorella) and temperature (22° and 28 °C) on competition among the rotifers Brachionus calyciflorus, Brachionus havanaensis, Brachionus patulus and Brachionus rubens, based on population growth experiments for 24 days. The growth experiments were conducted seperately for each individual rotifer species (i.e., controls), and in mixtures of all four species in equal initial proportions (i.e., under competition). The population growth of B. calyciflorus, B. havanaensis, B. patulus and B. rubens grown separately at two temperatures and at three algal food densities showed typical patterns of lag, exponential and retardation phases in the controls. This pattern differed considerably under competition. In general, we observed that in all of the test species, the highest growth rates were observed at higher food levels and in the absence of congenerics. At 22 °C, under the lowest food level, the differences in the population abundances of B. havanaensis, B. patulus and B. rubens grown alone and in the presence of competition were large. However, these differences reduced as food density was increased from 0.5 × 10⁶ to 4.5 × 10⁶ cells ml⁻¹. At 28 °C and at the lowest food level, all of the other rotifer species eliminated B. havanaensis in mixed cultures. Each brachionid species had a higher rate when grown alone than when cultured with other species. The highest r (mean ± standard error: 0.54 ± 0.01 day⁻¹) was recorded for B. havanaensis at 28 °C under 4.5 × 10⁶ cells ml⁻¹ of algal food density. At 28 °C at low algal food density, the presence of competitors resulted in negative population growth rates for three of the four rotifer species tested.     

Feeding behaviour and morphology of filtering combs of Daphnia galeata

The population of Daphnia galeata Sars from the fish pond Velký Pálenec (Blatná, Czechoslovakia) living in high food conditions (7 mgC l^–1) was characterized by a small size of the filtering comb on the thoracic limb 3, measured as seta length, length of the base of the comb and number of setae (population 1). One month cultivation of this population in low food conditions (1.5 mgC l^–1) in the laboratory resulted in twofold increase in size of the filtering comb (population 2). Filtering and ingestion rates of both populations were measured at eight concentrations of food (approximately 0.025–3.2 mgC l^–1) using ¹⁴C labeled Scenedesmus acutus. The results show that size of the filtering combs influences considerably feeding behavior of Daphnia. The comparison of animals with the same body length suggests that the population with a large comb feeds at concentration of food below 0.4 mgC l^–1 more intensively and reaches the maximum of the filtering rate at a lower concentration than the population with a small comb. The situation is opposite at concentration above 0.4 mgC l^–1. The higher values of theoretical flow in population with a small projection of filtering area suggest that this population has to compensate disadvantage of a small comb with the higher appendages beat frequency.     

Suspension feeding in Bithynia tentaculata (Prosobranchia,Bithyniidae), as affected by body size,food and temperature

The suspension feeding of Bithynia tentaculata was tested in laboratory experiments. The animals were fed in 1-1 aerated glass beakers, and filtration rates were calculated from changes in cell concentrations during the 6-h experiment. Temperature influenced the filtering rate, with minimum values of 5ml · ind^–1 · h^–1 at 5° C and maxima of 17.2 ml · ind^–1 · h^–1 at 18° C. Three food species of different size, motility and cell surface characteristics (Chlamydomonas reinhardii, Chlorella vulgaris and Chlorogonium elongatum) did not affect filtration rates. Suspension feeding increased with increasing food concentrations up to 12 nl · ml^–1, above which feeding rate was kept constant by lowering the filtering rates. Even the smallest animals tested (<4 mm body length) were found to be feeding on suspended food at a rate of 2.7 ml · ind^–1 · h^–1, and increasing rates up to 8.4 ml were found in the 6–7 mm size class. All size classes of Bithynia showed a circannual fluctuation of their filtration rates. The ecological consequences of Bithynia's ability to switch between two feeding modes, grazing and suspension feeding, are discussed.     

A Bioenergetic Analysis of Factors Limiting Brown Trout Growth in an Ozark Tailwater River

We examined prey utilization and energy consumption by brown trout, Salmo trutta, in a cold tailwater (Little Red River, Arkansas, USA; LRR) having low biodiversity and low availability of fish as prey. Stomach content analysis and age estimation were performed on thirty brown trout (10 each of three size classes for a total of 710 trout) collected monthly from an upstream and downstream site over a 1-year period. Diet diversity was low at both sites, as 80% and 70% of all prey consumed by upstream and downstream brown trout, respectively, were isopods. Piscivory (<0.5% of individuals sampled) and consumption of terrestrial invertebrates were rare. There was no relation between diet diversity and trout age, and a very small ontogenetic shift in brown trout diet. Second, we investigated brown trout growth rates relative to prey consumption and temperature. Temperatures and availability of prey were less than required for maximal trout growth. However, prey availability limited trout growth directly, but sub-optimal temperatures probably buffered the effect of this reduced energy consumption by reducing metabolic energy expenditures. Brown trout growth was 54.8–57.0% of the maximum predicted by a bioenergetics model. Instantaneous growth rates for age 1 and adult brown trout were slightly higher for those downstream (0.195) versus those upstream (0.152). Although isopods are abundant within this tailwater to serve as a forage base, the displacement of native fish fauna and subsequent lack of establishment of cold-tolerant forage fish species due to the thermal regime of hypolimnetic release from Greers Ferry Reservoir probably serves as a major barrier to brown trout growth.