Channel catfish (Ictalurus punctatus) fingerlings were fed semipurified diets containing 0–150 mg/kg of vitamin C for 14 wk and subsequently at two temperature regimes infected with the pathogenic bacterium Edwardsiella tarda. Mortality rates were determined 96 h after infection. A supplemental vitamin C level of 30 mg/kg of diet was sufficient for normal growth and for prevention of deficiency signs such as lordosis, scoliosis, and a reduction in bone collagen formation. However, increased resistance against infection was provided when the level of supplemental vitamin C was increased to the highest dietary level, 150 mg/kg, at a water temperature of 23 °C. At 33 °C, increasing the supplemental level of vitamin C had significantly less effect on resistance against infection. The difference in response at the two temperatures indicates that the vitamin C requirement for resistance to infection is possibly higher when channel catfish are infected at lower temperatures, where the natural resistance is reduced, than when infected at a temperature near optimum for the natural resistance mechanisms of the fish.Key words: vitamin C, channel catfish, disease resistance, Edwardsiella tarda, infection

Responses of Nile tilapia in terms of growth, histological anomalies, and biochemical changes to subchronic and toxic concentrations of fumonisin B1 (FB1) and moniliformin (MON) were evaluated under controlled environmental conditions. Nile tilapia fingerlings (2.7 g) were fed diets containing 0, 10, 40, 70, 150 mg/kg of either FB1 or MON for 8 weeks. These mycotoxins were obtained from Fusarium moniliforme or Fusarium proliferatum culture materials, respectively. Among tilapia fed diets containing MON, fish fed either 70 or 150 mg MON/kg diet had significantly (P<0.05) lower mean weight gains than the control fish. However, tilapia fed diets containing FB1 at levels of 40 mg/kg or higher had significantly lower mean weight gains than the control fish. Mortality was low; differences in percent survival among diets were not observed. Hematocrit was significantly reduced only in fish fed diets containing 150 mg of FB1 or MON/kg diet. Serum pyruvate levels were significantly higher than control fish for all tilapia fed MON. The ratio between free sphinganine and free sphingosine (SA/SO) in liver increased significantly in fish fed the diet containing 150 mg FB1/kg. No histopathological lesions were observed in tilapia fed diets containing either MON or FB1. Responses of Nile tilapia in this study to dietary FB1 and MON demonstrate that both mycotoxins are toxic to tilapia and could reduce the productivity of this fish.

Responses of Nile tilapia to varying concentrations of aflatoxin B1 (AFB) were investigated under controlled laboratory conditions. Nile tilapia (2.7 g) were fed semipurified diets containing 0, 0.25, 2.5, 10, or 100 mg AFB/kg of diet for 8 weeks. Weight gain and hematocrit of fish fed with 0.25 mg AFB/kg were not significantly different from that of the control; however, diets containing higher levels of AFB had significantly (P<0.05) reduced weight gain and hematocrit. Histologically, livers of fish fed with diets containing 10 mg AFB/kg contained excess lipofuscin and irregularly sized hepatocellular nuclei. Diets containing 100 mg AFB/kg caused weight loss and severe hepatic necrosis; 60% of the fish in this treatment died by the end of the 8-week feeding period. No lesions were observed in the spleen, stomach, pyloric intestine, head kidney, or heart of fish in all treatments. These results indicate that acute and subchronic effects of AFB to Nile tilapia are unlikely if dietary concentrations are 0.25 mg/kg or less.

A study was conducted to determine if channel catfish yield in ponds can be maintained with reduced feed allowance, while increasing protein concentration in the diet. Channel catfish (Ictalurus punctatus) fingerlings (16.7 g average wt.) were stocked in twenty 400-m2 earthen ponds at a density of 13,750 fish/ha. Diets were prepared to contain three percentages of protein (P) at constant and variable digestible energy (DE) concentrations. One group of diets contained 28%, 32% or 36% protein and a constant level of DE, 3.08 kcal/g of diet. Another group of diets contained the same series of protein percentages and variable levels of DE, 2.70, 3.08 and 3.41 kcal/g, so that DE/P ratio was constant at 9.6 kcal/g. The diet containing 28% protein and 3.08 kcal DE/g diet was the control which was fed at satiation rate. The daily allowance of all the other diets was based upon the amount of protein consumed by the control fish; all treatments received the same daily protein allowance. Therefore, fish fed with the 32% protein diet received 12.5% less feed than the control and those fed with 36% protein diet received 22.2% less than the control. The feeding trial lasted 19 weeks, from June 1 to October 5. When DE level of the diets was constant at 3.08 kcal/g, weight gain of fish was not different (P>0.05) from the 28% protein treatment (satiation fed) and the 32% protein treatment (87.5% of satiation), but weight gain was lower (P<0.05) in the 36% protein treatment (77.8% of satiation). When the DE level of the diets changed in proportion to the protein content to provide a constant DE/P ratio, weight gain for the 32% protein treatment (87.5% of satiation) was higher (P<0.05) than that of the 36% protein treatment (77.8% of satiation), but not different (P>0.05) from the 28% protein treatment (100% of satiation). Feed efficiency ratio (FER) improved (P<0.05) as protein level increased from 28% to 32%, with a 12.5% decrease in feed allowance, at constant and variable DE levels; however, FER did not improve (P>0.05) as protein level increased from 28% to 36%, with a 22.2% reduction in feed allowance. There was no difference (P>0.05) in total ammonia nitrogen (TAN), nitrite nitrogen, biochemical oxygen demand (BOD5), chlorophyll a or soluble phosphorus in pond water among treatments; however, TAN, nitrite nitrogen, and BOD5 changed (P<0.05) over time as feed allowance increased. Among the treatments evaluated, commercial fish farmers may find the 32% protein, 3.08 kcal/g DE and 87.5% satiation regimen, the most practical since they can feed to less than satiation, obtain a better FER, and optimize production.

Earthy-musty off-flavor in channel catfish can adversely affect the catfish industry if strongly off-flavored fish reach the market. Pre-harvest sensory evaluation of fish is commonly performed by processing plants for detecting unacceptable levels of off-flavor. In West Alabama, three to 12 fish are sampled over a period of up to 3 weeks before harvest. Despite this effort, off-flavored catfish regularly reach the market. A study was conducted in summer and fall on ten commercial catfish farms to determine the fraction of off-flavored fish in ponds. Flavor was assessed by sensory evaluation. A larger occurrence of off-flavor was found in summer than in fall. Fraction of off-flavored fish varied from 0 to 54% depending on the pond and the acceptance criterion used. Between-pond variance of the fraction of unacceptable fish was greater than within-pond variance. Therefore, Bayesian sampling should be used instead of conventional sampling based on the binomial function. Different sampling plans are proposed depending on levels chosen for producer and consumer risks. It was recommended to consider a sample size of at least 30 fishes.

Growth, histological lesions, and biochemical changes were investigated in channel catfish Ictalurus punctatus fed various concentrations of moniliformin with or without fumonisin B-1. Channel catfish (average initial weight, 1.5 g) were fed diets formulated to contain 0, 20, 40, 60, and 120 mg moniliformin/kg; 0, 20, and 40 mg fumonisin B-1/kg, or two combinations of moniliformin and fumonisin B-1 for 10 wk. Fish fed diets with the lowest concentration of moniliformin or fumonisin B-1 (20 mg/kg diet) had significantly (P < 0.05) less weight gain than the control fish. Increasing the level of moniliformin in the diets resulted in a linear decrease in weight gain. Overall mortality of fish was 4% and not related to treatment effects. Hematocrit was significantly (P < 0.05) lowered by 60-mg moniliformin/kg diet or 40-mg fumonisin B-1/kg diet. Dose-dependent increases in serum pyruvate concentration and ratio of free sphinganine to free sphingosine were obtained with increasing concentration of dietary moniliformin and fumonisin B-1, respectively. Mean serum pyruvate level was significantly (P < 0.05) higher in fish fed the diet containing 60-mg moniliformin/kg diet. Addition of fumonisin B-1 (40 mg/kg) to the diet containing 40-mg moniliformin/kg significantly increased the serum pyruvate level above that of the control. Also, the lowest concentration of fumonisin B-1 (20 mg/kg diet) significantly (P < 0.05) increased the ratio of sphingolipids. Combinations of moniliformin and fumonisin B-1 at levels of 20:40 and 40:40 mg/kg diet did not significantly change the effect of fumonisin B-1 on the ratio of sphingolipids. The only tissue lesions observed in liver and heart were smaller nuclei of cells in livers of fish fed diets containing the two highest levels of moniliformin and the combinations of the two toxins.

Three feeds with different concentrations of crude protein were applied to 400 m(2) channel catfish ponds at the Auburn University Fisheries Research Unit. Fish were fed to satiation with the 28% crude protein feed; the other two diets (32% and 36% crude protein) were applied in amounts calculated to provide the same crude protein input as for the 28% crude protein diet treatment. Using this practice, feed application decreased as feed crude protein increased; likewise, phosphorus and organic matter loads to the ponds decreased. The feeding practice and diets used in this study had no measurable effects on nitrogen concentrations in pond waters and effluents or on fish production. Despite the smaller phosphorus inputs with 32% and 36% protein feed, only a small fraction of the applied phosphorus remained in the water column. The differences in phosphorus input among treatments did not affect phosphorus concentrations in pond water or effluents. When fishponds were drained for harvest, the quality of the effluent did not change until about 75% of the water had been released. The water quality in the effluents then deteriorated because the pond bottom was disturbed by the outflowing water, fish activity and harvest. By holding the last 25% of the water in the ponds for 12- 24 h after fish harvest, much of the suspended matter was removed by sedimentation. The water can then be released slowly to prevent resuspension of the sediment and obtain a better quality effluent.

Nutritional requirements for catfish (Ictalurus punctatus) feeds based solely on maximizing growth may not lead to the best economic performance. In addition, the choice of protein level may have important implications for dress‐out percentages in the processing sector. Processors may be able to send pricing signals to farmers to improve processing efficiencies. The objectives of this paper are to quantify the economic incentives to use different protein levels in catfish feeds and to investigate the possibility of processor incentives to affect these decisions. Data from research ponds, in conjunction with pricing and cost data, were used to quantify the changes in net returns associated with alternative protein levels. Both experimental results and estimates using commercial practices were developed. In addition these data were utilized in developing price premiums that might be implemented by the processing sector to provide incentives that would result in higher dress‐out percentages and thus greater processing efficiency. In a restricted‐feeding regime, selection of the higher protein feeds resulted in higher net returns, however, in a satiation‐feeding regime, lower protein levels resulted in higher net returns. Specifically, catfish enterprise profitability could be enhanced by feeding a 38% protein ration when fish are fed on a restricted basis whereas, in a satiation‐feeding regime profitability could be enhanced by feeding a 26% protein ration. Results indicate that the potential for a price premium policy that encourages a higher dress‐out percentage might be adopted in the future by the’ catfish processing sector as has been done in other meat processing industries. Keywords: Aquaculturenutritionprice premium

Young-of-year channel catfish Ictalurus punctatus were fed an egg-white-based purified diet supplemented with serial concentrations of phosphorus from monosodium phosphate for 10 weeks: they were subsequently challenged by a 24-h immersion in a cell suspension of Edwardsiella ictaluri (10(5.4) cells/ml) at 25 +/- 1 degrees C. Fish responses, which included weight gain, serum phosphorus concentration, serum alkaline phosphatase activity, mortality of challenged fish, and antibody production, were compared with dietary phosphorus concentration by regression analysis. Significant (P < 0.05) quadratic responses occurred in weight gain, serum alkaline phosphatase activity, mortality of challenged fish, and antibody production, Serum phosphorus concentration showed a significant linear response. The break points in the quadratic response curves showed that 0.38, 0.40, and 0.42% dietary phosphorus amounts were required for maximum alkaline phosphatase activity, survival from E. ictaluri challenge, and weight gain, respectively. This study showed that dietary phosphorus concentration influences the resistance of channel catfish to E. ictaluri challenge and that the dietary requirement for maximum weight gain is sufficient for maximum resistance against E. ictaluri challenge in young fish.

Overwintering is a major source of uncertainty for US catfish farmers, particularly decisions on feeding. To address this issue, economic analysis was undertaken using results from pond experiments. Three overwintering strategies (full‐feed, partial‐feed, and no‐feed) for two year classes of catfish were compared. Year 1 fin‐gerlings were 22 g and year 2 fish were 420 g at stocking. Winter feeding was based on temperature and body weight percentages; (1) full‐feeding followed the regime during the November to April period; (2) partial‐fed treatments followed the temperature/body weight regimen only during the months of November, March and April, with no feeding during the coldest months of December to February; and (3) no‐feeding treatments received no feed during the overwinter period. Cost and returns were estimated for each alternative and each alternative was assessed using: (1) overwinter period experimental results, (2) overwinter period experimental results extended through the grow‐out period, (3) overwinter period experimental results extended to minimally acceptable fish sizes, and (4) adjusted estimates to reflect commercial‐scale practices. Sensitivity analyses on feed conversion ratios, stocking rates and fish selling prices were also conducted on commercial‐scale enterprises. Results consistently showed partial‐fed overwinter practices to be most profitable. Secondly, year 1 fish always had higher returns than year 2 fish due largely to the additional overwintering period and associated variable and fixed costs incurred by the year 2 fish production practices. The data upon which this analysis was based do not include the possibility of having a harvest‐sized fish going into the winter period.

Phosphorus budgets were prepared for channel catfish Ictalurus punctatus ponds at Auburn, Alabama, that received one of five diets ranging from 0.60 to 1.03% phosphorus. Fish production did not differ (P > 0.05) among diets. There were few differences among treatments with respect to soluble reactive phosphorus, total phosphorus, and chlorophyll a concentrations or gross primary productivity, Phosphorus loss in effluents when ponds were drained for harvest did not differ among treatments (P > 0.05). Phosphorus removed from ponds in fish at harvest and the amounts of phosphorus adsorbed by bottom soils increased as dietary phosphorus concentration increased (P < 0.05). Low-phosphorus diets did not decrease phytoplankton productivity or improve effluent quality. Uptake of phosphorus by bottom soils is a major factor controlling phosphorus concentrations in pond water. Low-phosphorus diets fan be beneficial in catfish pond management by reducing the phosphorus load to bottom soils and conserving their ability to adsorb phosphorus.

Three trials were performed to identify feed enhancers for largemouth bass. Fish trained on dry pellets were stocked into 45 1 aquaria. Trial 1 evaluated the palatability of diets in which fish meal (FM) was replaced with 0, 20, 40, and 60% soybean meal (SM-00, SM-20, SM-40 and SM-60). Feed intake declined as dietary concentration of soybean meal increased (P < 0.01). SM-60 was used as the control and basal diet in trials 2 and 3. Trial 2 tested the following mixture of substances: (1) amino acids: alanine, glycine, proline, serine, leucine, valine, histidine, and tryptophan; (2) nucleotides: inosine and inosine-5-monophosphate (IMP-5′); (3) betaine. Dietary concentrations of chemicals were kept in the same molar ratio as in aqueous krill (Euphasia pacifica) extract. Chemical groups were tested alone or in all possible combinations. Nucleotides alone enhanced feed intake of fish by 46% compared with the control diet (P < 0.05), while amino acids and betaine were ineffective (P > 0.05). No additive effects among chemical groups were observed (P > 0.05). In trial 3, inosine and IMP-5′ were tested alone at 1400, 2800, and 5600 mg kg−1 of feed or together, each at 2800 mg kg−1 of feed. A diet with 10% fish meal (FM-10) was also evaluated. Effective dietary concentration of IMP-5′ seems to be about 2800 mg kg−1 of feed which gave a feed intake 23% higher than the control diet (P < 0.05). Dietary IMP-5′ level of 5600 mg kg−1 of feed failed to further increase feed intake (P > 0.05). Inosine was not an effective feed enhancer at the dietary levels tested (P > 0.10). No significant additive effect of inosine in a diet flavored with IMP-5′ at 2800 mg kg−1 of feed was found (P > 0.10). Feed intake was highest for fish fed FM-10 (P < 0.01), about 58% superior than feed intake for the control diet. This study showed that IMP-5′ and fish meal were effective feed enhancers, while increasing dietary concentration of soybean meal depressed feed intake of largemouth bass.

Channel catfish (Ictalurus punctatus) fingerlings (average initial weight, 1.70g) were fed casein-based purified diets supplemented with 0, 0.02, 0.06, 0.20 or 0.40 mg of selenium per kg from sodium selenite (Na2SeO3), selenomethionine (Se-M) or selenoyeast (Se-Y) for 9 weeks. Data for weight gain and glutathione peroxidase activity were subjected to regression analysis to determine dietary requirements and relative bioavailability for the various selenium sources. Broken-line analysis showed that minimum supplemental dietary selenium requirements as Na2SeO3, Se-M and Se-Y for weight gain were 0.28, 0.09 and 0.11 mg kg−1, and for liver glutathione peroxidase activity were 0.17, 0.12 and 0.12 mg kg−1 diet. Relative bioavailability values of Se-M and Se-Y compared to Na2SeO3 were 336 and 269% for growth, and 147 and 149% for glutathione peroxidase activity, respectively. Selenium from Se-M and Se-Y showed significantly higher rates of accumulation in liver and muscle than selenium from Na2SeO3. This study indicates that selenium allowance in diets of channel catfish can be reduced when selenomethionine or selenoyeast replaces inorganic selenium.

Two 10-week feeding experiments were conducted with channel catfish fingerlings in aquaria to compare the efficiency of utilization for growth of free versus protein bound lysine in practical diets. In experiment 1, a basal, 26% protein diet, deficient only in lysine, was formulated with a combination of peanut meal and corn gluten meal as the primary protein source. The diet was then supplemented with graded levels of lysine by either adding l—lysine · HCl or substituting soybean meal for the peanut meal—corn gluten meal combination to produce two series of diets with increasing concentrations of either free lysine or protein-bound lysine. In experiment 2, the basal diet contained sesame meal as the primary protein source and was supplemented with free or protein-bound lysine as in experiment 1. Slope ratio analysis of response data showed that the efficiency of utilization of protein-bound lysine in soybean meal relative to free lysine from lysine-HCl was 196 and 163% for experiments 1 and 2, respectively, based on weight gain. A subsequent feeding experiment was conducted in which the peanut meal-corn gluten meal basal diet was supplemented with lysine alone or with lysine plus histidine, isoleucine, threonine, and tryptophan to match the essential amino acid composition of the diet in which soybean meal provided the protein. Supplementation of the basal diet with the additional amino acids did not improve fish weight gain relative to that from supplementation with lysine alone. Overfortification of the basal diet with free lysine improved weight gain of fish to equal that obtained with the diet containing soybean meal. Loss of lysine due to leaching of diets in water was 12.7 and 2.0% of the original lysine concentration for free lysine and protein-bound lysine, respectively. When leaching losses are subtracted from the lysine concentrations in the test diets, the efficiency of utilization of protein-bound lysine is still higher than that of free lysine, 175 and 146%, based on weight gain, for experiments 1 and 2, respectively. These results indicate that protein-bound lysine is more efficiently utilized than free lysine in practical type diets for young channel catfish.

Coefficients of net absorption for copper, iron, manganese; selenium, and zinc mere determined for chelated sources (copper proteinate, iron proteinate, manganese proteinate, selenium proteinate, zinc proteinate) and inorganic sources (copper sulfate pentahydrate, ferrous sulfate heptahydrate, manganese sulfate monohydrate, sodium selenite, zinc sulfate heptahydrate) of these elements with channel catfish Ictalurus punctatus. Fish weighing approximately 60 g were placed into 40-L aquaria (12 fish/aquarium) at a temperature of 28 +/- 2 C and fed either an egg white-based, purified diet or a soybean meal-based, practical diet with and without the test mineral sources for 6 wk then killed and feces collected from the hindgut. Treatments were arranged in a 2 x 2 factorial design. Absorption coefficients for the elements in the basal and mineral supplemented diets were calculated by the indirect indicator (chromic oxide) method and corrected for residual amounts of element in the basal diets. Net absorption of the chelated minerals was significantly higher (P < 0.05) than net absorption of the inorganic minerals in both basal diets. Average percentage improvement in net absorption of chelated minerals over inorganic minerals was 39.3% in the purified diets and 81.1% in the practical diets. These results may indicate that appreciably lower amounts of chelated trace minerals than inorganic trace minerals can be used as supplements in catfish feeds.

Year-2 channel catfish (average weight 765 g) were fed a commercial-type, all-plant diet containing supplemental phosphorus (0.40%) from one of various sources, or fungal phytase (1,000 and 3,000 units), in 1-m(3) circular raceways for 21 d at a temperature of 28-30 C. subsequently, net absorption of phosphorus from the diets was determined by the chromic oxide indicator method in which feces were collected from the rectum. Net absorption of the supplemental phosphorus was corrected for the absorbed residual phosphorus in the basal diet. Net absorption coefficients for monosodium phosphate. monoammonium phosphate, finely ground defluorinated rock phosphate and monocalcium phosphate were 88.6, 85.4, 81.7, and 81.2%, respectively, and were not significantly different. Net absorption coefficient for dicalcium phosphate was significantly lower, 74.8%, but was significantly higher than those for coarsely ground defluorinated rock phosphate and tricalcium phosphate, which were 55.1 and 54.8%, respectively. These data are in general agreement with relative bioavailability values based on growth response for channel catfish determined in other research, and should be appropriate for determining available phosphorus allowances in commercial feeds and establishing phosphorus budgets in aquaculture feeding operations. The net absorption of phosphorus from the all-plant basal diet was 31.2% and increased significantly to 55.1 and 62.5% with the addition of 1,000 and 3,000 units of fungal phytase, respectively.

A pond study was conducted from November 1 through April 30 with young (age 0; average size, 43 g) and market-size (age-2; average size, 660 g) channel catfish Ictalurus punctatus to compare three management regimens: no feeding, partial feeding (no feeding in December, January, and February), and continuous feeding according to fish size and water temperature. Weight change, feed conversion ratio, and responses to experimental challenge with Edwardsiella ictaluri were evaluated. No significant difference in weight gain occurred between partially fed and continuously fed fish in either age-group; average weight increase for fed age-0 fish was 99% and for fed age-2 fish was 38%. The nonfed age-0 fish lost 12.3% and the nonfed age-2 fish lost 78 of their initial weight. Feed conversion ratios were significantly lower in partially fed fish than in continuously fed fish in both age-groups. Mortality from E. ictaluri challenge among age-0 fish was significantly higher in the nonfed fish, but among the age-2 fish, mortality was significantly lower in the nonfed fish. No difference in mortality rate occurred between partially fed and continuously fed fish in either age-group. Starvation induced lower antibody production against E. ictaluri antigen in the age-0 fish but higher antibody production in the age-2 fish. Phagocytic index was lower in nonfed fish than in fed fish from both age-groups. This study indicates no benefit from feeding age-0 and age-2 channel catfish during December, January, or February if feeding is reintroduced in March and continued through April. Although starvation was immunosuppressive in small channel catfish, it enhanced resistance to bacterial infection in larger fish. However, more research information is needed before reduced feeding can be recommended to enhance resistance of channel catfish to E. ictaluri.