The dietary protein requirement of a bagrid catfish, Mystus nemurus (Cuvier & Valenciennes), determined using semipurified diets of varying protein level

Triplicate groups of Mystus nemurus (Cuvier & Valenciennes) were fed isoene rgetic semipurified diets containing seven dietary protein levels from 200 to 500 g kg(-1) diet for 10 weeks. Dietary protein was supplied by graded a mounts of a protein mixture (tuna muscle meal:casein:gelatine) at a fixed r atio of 50:37.5:12.5. Mystus nemurus fingerlings of initial weight 7.6 +/- 0.2 g were fed close to apparent satiation at 2.5% of their body weight per day in two equal feedings. Growth performance and feed utilization efficie ncy increased linearly with dietary protein level from 202 to 410 g kg(-1) diet and declined with protein levels of 471 g kg(-1) diet or above. Protei n efficiency ratio and apparent net protein utilization started to decline when the fish were fed with dietary protein levels exceeding 471 g kg(-1) d iet. Fish fed with lower protein diets (202-295 g kg(-1) diet) had signific antly (P < 0.05) higher carcass lipid content compared with fish fed with h igher protein diets. Carcass lipid contents were inversely related to moist ure content. Dietary protein did not significantly affect fish carcass prot ein and ash content. Using two-slope broken-line analysis, the dietary prot ein requirement for M. nemurus based on percentage weight gain was estimate d to be 440 g kg(-1) diet with a protein to energy ratio of 20 mg protein k J(-1) gross energy. This level of protein in the diet is recommended for ma ximum growth of M. nemurus fingerlings weighing between 7 and 18 g under th e experimental conditions used in this study.