Evaluation of Protein Reduction and Lysine Supplementation of Production Diets for Channel Catfish

Abstract

A 2-year continuous production trial was conducted in earthen ponds to evaluate lysine supplementation of practical diets as a means of reducing the need for total dietary protein and limiting the nitrogenous waste production of channel catfish Ictalurus punctatus. Fingerling channel catfish with an initial weight of 34.1 g were stocked in twelve 0.04-ha ponds in early summer at a density of 24,710 fish/ha. The experimental diets consisted of three practical diets containing 30% crude protein (control), 25% crude protein, or 25% crude protein supplemented with 0.5% lysine·HCl to provide the same level of lysine as the control diet. Each diet was fed to fish in four replicate ponds to apparent satiation once a day when water temperature was greater than 15°C. Ponds were top-harvested three times during the study with a 4.1-cm-mesh grader seine to remove marketable fish. The yields of marketable fish at each harvest period were not significantly (P > 0.05) affected by diet. Following each harvest, fingerlings (average weight at restocking = 13.2, 29.5, and 50.8 g, respectively) were stocked at the rate necessary to replace the harvested fish plus 25%. At the end of 2 years, all fish were harvested to obtain final production data. Percent recovery over the entire study was high (84–91%) and not affected by diet. However, final harvest data showed a significant (P < 0.05) effect of diet on fish size, with ponds containing fish fed the 30%-crude-protein diet having a higher percentage of marketable fish. The total yield of fish fed the 30%-crude-protein diet averaged 16,546 kg/ha, while fish fed the 25%-crude-protein diet and the 25%-crude-protein diet supplemented with 0.5% lysine·HCl had average yields of 14,838 kg/ha and 14,363 kg/ha, respectively; the latter two were not statistically different from that of the 30%-crude-protein diet. Feed conversion ratios were unaffected by dietary protein level or lysine supplementation. Water quality was affected by dietary treatment, with total ammonia nitrogen concentrations in ponds with fish fed the diet with 25% crude protein plus lysine significantly elevated (0.6 ± 0.39 mg/L) relative to those in the control ponds (0.54 ± 0.30 mg/L); ponds with fish fed the 25%-crude-protein treatment had lower ammonia concentrations (0.47 ± 0.32 mg/L) than the controls. Nitrite concentrations were significantly higher in control ponds than in the other treatment ponds, but nitrate levels were unaffected by dietary treatment. Based on this study, it appears that the reduction of dietary crude protein from 30% to 25% had limited effects on channel catfish production. Dietary treatments also had quantitatively small effects on water quality, and supplemental lysine provided no appreciable benefits in terms of yield or water quality.