Optimum Dietary Threonine Level for Juvenile Japanese Flounder Paralichthys olivaceus

Abstract

A 6-week feeding trial was conducted to estimate the optimum threonine level in the diet for growth of juvenile Japanese flounder, Paralichthys olivaceus with six test diets (50% crude protein) containing intact proteins (casein and gelatin) and a mixture of L- crys- talline amino acids (CAA) as nitrogen sources. CAA were supplemented to correspond to the amino acid pattern found in the whole body protein of the Japanese flounder except for threonine. Test diets containing precoated CAA with six graded levels of threonine (0.80 to 2.72% of diet or 1.60 to 5.44% of protein) were fed to triplicate groups of the ju- veniles (2.00 ± 0.05 g) twice a day for six weeks at 5% body weight. Results showed that the weight gain, feed intake, feed conversion efficiency (FCE), specific growth rate, per- cent survival and nitrogen retention in the whole body were significantly (P<0.05) affected by dietary threonine levels. The optimum threonine level in the diet of Japanese flounder based on broken-line analyses of percent weight gain was 1.57% of diet or 3.14% of pro- tein. Broken-line analysis of FCE and nitrogen retention indicated that the optimum di- etary threonine level was 1.60 and 1.61% of diet (3.20 and 3.22% of protein) respectively, close to the value estimated by the weight gain data.