Effect of varying protein levels on growth and digestive enzyme activities of pengba Osteobrama belangeri (Valenciennes, 1844)

Pengba, Osteobrama belangeri (Valenciennes, 1844) is considered as one of the candidate species for diversification of aquaculture. However, only scanty information is available on its nutrient requirements. Hence, the present study was conducted on growth and digestive enzyme activities of pengba fry in response to different dietary protein levels. Six semi-purified isocaloric diets were formulated with different levels of protein at 5% increments (25, 30, 35, 40, 45 and 50%) and fed to different groups of pengba fry for a period of 60 days. Survival of fish was significantly influenced by different protein levels (p<0.05). The highest weight gain% and specific growth rate (4.17% day(-1)) was obtained at 45% protein level which thereafter declined. The best feed conversion ratio (1.46) was observed at 45% protein level and the highest protein efficiency ratio (2.14) was obtained at 25% protein level with significant difference (p<0.05). The crude protein content of fish was significantly affected by dietary protein levels (p<0.05) and highest was recorded at 45% protein diet. Moisture, ether extract and ash content did not show significant (p>0.05) variation among dietary treatments. The activity of proteolytic enzymes (proteases, typsin and chymotrypsin) and acid phosphatase were signicantly (p<0.05) enhanced by dietary protein levels up to 45%, which were found to decline thereafter. Amylase activity was significantly decreased as protein levels increased in the diet. Lipase and alkaline phosphatase activities were not influenced by dietary protein levels. In the present study, penbga fry fed with 45% protein diet, showed the best growth performance and highest digestive enzyme activities. The activity of digestive enzymes in the gut clearly demonstrated that the proteolytic enzymes are activated in response to dietary protein utilisation and also revealed that pengba fry may require high protein (45%) diet for better growth and survival. Second order polynomial regression analysis revealed that the maximum protein requirement of pengba fry was 45.1% (r(2) = 0.90). The findings of the study is expected to have significant implications for feed development for pengba aquaculture.