DIETARY PROTEIN REQUIREMENT FOR JUVENILE SPINIBARBUS SINENSIS

The objective of th is studywas to investigate the dietary protein requirement of the juvenile Spinibarbus sinensis and determine effects of dietary protein levels on feed intake, growth and nutrition utilization. W hite fish mealwas used as the dietary protein source, and six isocaloric expermi ental diets were formulated to contain d ifferent protein levels of 20.49%, 26.48%, 34.20%, 41.02%, 49.94% and 55.86% (referred to as D1, D2, D3, D4, D5 and D6 respectively). Each treatment had four replicates and 12 fish (in itialweight of (10.36 ± 1.40) g (mean ± S.D.)) of each replicatewere reared in a circulated filtered system for 10 weeks at (27.5 ± 0.5) e in a circu lated filtered rearing system. Fish were hand fed to satiation once daily at 18: 00. Feceswere collected from the second week by siphoning and washed mi med iately everyday. A sample of 9 fish at the start of feeding expermi ent and 4 fish per group at the end of expermi ent were sampled and stored frozen at-26℃ for proxmi ate composition analysis1 Fish were weighted individually after 48h starvation at the end of the expermi ent. The results showed that as dietary protein increased, the feeding rate of drymatter (FRdm) decreased gradually from　D1 toD4 firstly, and then leveled off1However, a positive correlation between the feeding rate of protein (FRp) and die-tary protein levels was found (r= 0.982,ppSGRw), specific growth rates　of energy (SGRe) and feed efficiency (FE) were significantly increased from D1 up toD4 (pSGRw, SGRe and FE reached a plateau and did not d iffer significan-tly among D4, D5 and D6. Protein efficiency ratio (PER) decreased from 178.23 to 116.60% as dietary protein level increased from D1 to D6. Values of protein productive values (PPV) had a smi ilar trend like PER, which decreased from 23.92 to 18.62% as dietary protein levels increased from D1 to D6. Energy productive values (EPV) significantly in-creased from (20.05 ± 0.39) to (28.87 ± 0.81)% as dietary protein increased from D1 to D4, then decreased to (23.49 ± 2.00)% for D6. Based on the broken linemodels between SGRw, SGRe, FE and d ietary protein levels, the optmi al d ietary protein requirement for juvenileS. sinensis was estmi ated to be 39.6% -42.2% when wh ite fish mealwas the sole protein source and the dietary energy valuewas 15.71M J/kg. This optmi um d ietary protein level for juvenileS. sinensis is higher than some other omnivorous fishes. It suggested that the food hab it of juven ileS. sinensis preferring an-imal plankton and zooplankton make it need more dietary protein for growth1 Smi ultaneously, the growth rate of juvenile S. sinensis is slower than those of some other fish species, which could be due to its small diet intake ratio and low apparent digestibility of dietary protein.