Influence of dietary lipid/protein ratio on survival, growth, body indices and digestive lipase activity in Snakehead (Channa striatus, Bloch 1793) fry reared in re-circulating water system

Nine isoenergetic (18.5 kJ g-1) diets were formulated in a 3 x 3 factorial design to contain three protein levels (350, 400 and 450 g kg-1) for each of three lipid levels (65, 90 and 115 g kg-1), respectively, and fed twice daily for 8 weeks to fish of mean initial weight 3.34 +/- 0.02 g reared in a re-circulatory water system. Temperature, pH and dissolved oxygen (DO) were maintained within the range 28-30 degrees C, 5.6-6.8 and 4.82-6.65 mg L-1 respectively throughout. Results show that fish survival was better in the groups fed 65 g kg-1 lipid while growth performance (% weight gain, WG; specific growth rate, SGR) and nutrient utilization (feed conversion ratio, FCR; protein efficiency ratio, PER; protein intake, PI) in the 65/450 and 90/450 g kg-1 treatments were similar and significantly (P < 0.05) higher than in fish fed the other lipid/protein ratio combinations. The body indices monitored (Hepatosomatic index, HSI and viscerosomatic index, VSI) were similar among the treatments whereas intestinal lipase activity was not significantly (P < 0.05) affected by increase in dietary lipid and protein levels. Carcass composition showed that dietary protein level affected body protein content positively in the 65 and 90 g kg-1 lipid treatments, but dietary lipid level did not affect body lipid content. A lipid/protein ratio of 65/450 g kg-1 is considered adequate for good growth performance and survival of Channa striatus fry.