Effects of pure and crude papain on the utilization and digestibility of diets containing hydrolysed feather meal by Nile tilapia (Oreochromis niloticus L.)

This study was conducted to evaluate the effects of pure and crude papain on the digestibility and utilization of diets containing hydrolysed feather meal (HFM) by Nile tilapia (Oreochromis niloticus L.) under indoor and outdoor conditions. O.niloticus fingerlings with a mean weight between 22 and 30g were stocked in aquaria and cages respectively. Recirculating water was used in the aquaria while cages were installed in an 800m2 earthen pond. The pond was fertilized with 20 kg N and 8 kg P ha-1 respectively. Liming was done once with 2500 kg ha-1 of CaCO3 at the beginning of the experiment. Five isonitrogenous (250g CP kg-1) and isocaloric (12.3 kJ g-1) diets designated as 1, 2 3, 4 and 5 were formulated. Diet 1 contained 6 % freshwater shrimp meal (FSM) and 4.5 % HFM and served as control, Two other diets were formulated from the control by adding pure papain (Diet 2) and 4.5 % PLM (crude papain) (Diet 3). The other two diets were formulated by completely replacing FSM with HFM plus pure papain (Diet 4) and crude papain (Diet 5). All fish were fed at 10% body weight day-1 in three replicates for 58 days. Results indicated that dietary levels of HFM and PLM above 4.5% led to significant (P < 0.05) growth reductions in aquaria. However, complete replacement of FSM with HFM did not significantly (P > 0.05) affect growth of fish in the cages. In both experiments, survival was similar among treatments, but protein digestibility decreased with increasing levels of HFM in the diet. In conclusion, a combination of the protein sources FSM, HFM and PLM gave the highest growth performance in both aquaria and cages. The growth depression observed for treatments 4 and 5 in aquaria was not observed in the cages, where the natural food may have provided an important nutrient supplement.