METHIONINE REQUIREMENT OF CHANNEL CATFISH FED SOYBEAN MEAL-CORN-BASEDDIETS

A soybean meal-corn-based diet was used to determine dietary methionin e (Met) required by 14-g channel catfish (Ictalurus punctatus) in a 42 -d experiment at 25 degrees C. The basal diet with balanced limiting a mino acids relative to the catfish whole-body amino acid profile conta ined 277 g of CP, 3.6 g of Met, 4.0 g of cystine (Cys), and 10 MJ of D E/kg of DM. DL-Methionine was added to the basal diet from 0 to 12.0 g /kg in 2-g intervals at the expense of L-glutamic acid to produce seve n isonitrogenous and isocaloric diets. A reference diet contained 331 g of CP, 8 g of Met, 5 g of Cys, and 10 MJ of DE/kg of DM (included 8% fish meal). Seven graded Met levels resulted in quadratic responses ( P < .01) of weight gain, specific growth rate, feed or GE intake, feed or energy efficiency, protein or energy retention, protein efficiency ratio, and apparent net protein or energy utilization. Channel catfis h required 9.4 g of Met/kg of DM (34.1 g/kg of CP) with a total 11.3 g /kg of calculated digestible sulfur-containing amino acids based on mu ltiple regression dose-response models or 270 mg of Met/kg of fish per day based on a broken-line response of protein gain to Met intake. At the adequate Met level, catfish with the lowest (P < .05) liver lipid s showed feed intake and protein or energy utilization efficiency simi lar (P > .05) to that of catfish fed the reference diet. Catfish fed a ll-plant-protein diets require more dietary methionine than previously reported. Catfish fed corn-soybean meal diets fortified adequately wi th methionine result in performance that approaches that of fish fed a fish meal-based diet.