Effects of dietary cottonseed meal protein levels on growth and feed utilization of Nile tilapia, Oreochromis niloticus L

The nutritional suitability and cost effectiveness of cottonseed meal (CSM) as protein source in the diet of Nile tilapia (Oreochromis niloticus L.) with mean initial weight 4.24±0.20 g, was evaluated over a 56-day growth period. Four isonitrogenous (320 g kg-1), isolipidic (100 g kg-1) and isoenergetic (18 KJ g-1) test diets were formulated in which CSM protein replaced fish meal (FM) protein at levels of 0% (control), 25%, 50% and 75%. The control diet had FM as the sole protein source. The growth experiment was conducted in plastic tanks in a recirculation system each dietary treatment was in triplicate. After 56 days of feeding fish at 6% - 4% body weight per day, CSM protein replacements of 25% and 50% did not significantly (P<0.05) affect growth (Specific Growth Rate, Weight Gain) and feed utilization (Feed Intake, Feed Conversion Ratio, Protein Efficiency Ratio, Apparent Net Protein Utilization and Energy Retention). However, the highest replacement level (75%) significantly reduced these parameters compared to the control diet and this was attributed to low levels of lysine, methionine and threonine and also to high levels of gossypol, trypsin inhibitors saponin and phytic acid in the diet. In terms of cost effectiveness, all the CSM based diets were more profitable than the control. The study indicated that CSM could replace at least 50% of fish meal protein in the diet of O. niloticus without adversely affecting growth and feed utilization and the most cost effective diet was also the diet with 50% inclusion level of CSM.