SUPPLEMENTAL EFFECTS OF METHIONINE-ENRICHED PLASTEIN IN PENAEUS-JAPONICUS DIETS

Two feeding trials were conducted to examine the effect of supplemental methionine (Met) as a crystalline amino acid or methionine-enriched soybean plastein (Met-PLS) on the weight gain, feed conversion efficiency (FCE), and protein efficiency ratio (PER) of the prawn Penaeus japonicus. In experiment 1, the juvenile prawns were maintained on diets containing the following nitrogen sources; diet 1 (basal), soybean protein-gelatin (3:1) + lysine HCl; diet 2, basal diet + crystalline Met; diet 3, basal diet (without lysine HCI) + soybean plastein (SB-PLS); diet 4, basal diet + Met-PLS; diet 5 (control), casein. In experiment 2, a similar feeding trial was conducted using test diets containing soybean protein-gelatin-casein-defatted salmon milt as a basal protein source; diet 6 (basal), diet 7, basal diet + crystalline Met; diet 8, basal diet + SB-PLS; diet 9, basal diet + Met-PLS. In experiment 1, supplementation of either crystalline Met, SB-PLS or Met-PLS did not improve weight gain, FCE, or PER of the prawns. In experiment 2, however, weight gain, FCE, and PER of the prawns were enhanced by supplementing diet 6 with Met-PLS but not with crystalline Met or SB-PLS. These results indicate that Met in soybean plastein is effectively utilized by the juvenile prawn for growth when added to Met-deficient diets containing small amounts of soybean protein. The present study suggests the possibility that Met-PLS has a higher bioavailability than crystalline Met as a methionine supplement for P. japonicus when added to methionine-deficient diets containing a certain minimum level of animal protein sources.