Use of tuna industry waste in diets for Nile tilapia, Oreochromis niloticus, fingerlings: effect on digestibility and growth performance
During the tuna canning process, about 52~54% of the total weight of the fish is discarded as waste, which can be processed in order to obtain tuna byproducts meal (TBM), or stabilized as tuna silage hydrolysates (TSH). Both products were tested as replacements of soybean meal (SBM), in diets for fingerling male Nile tilapia Oreochromis niloticus. Seven test diets were isonitrogenous (35% CP) and isoenergetic (19 kJ g-1): a basal diet contained SBM as main protein source (TSH0); four experimental diets had increasing inclusion levels of TSH replacing 25, 50, 75 and 100% of the SBM protein. The sixth diet contained TBM as sole protein source, and a commercial feed for tilapia was used as reference diet (RD). The diets were fed for eight weeks to triplicate tanks, each with 15 fry tilapia (initial weight of 0.89 ± 0.29 g). Tilapia fed the TBM diet had greater weight gain and feed intake, and lower feed conversion ratios than those fed diets containing with TSH. The RD, TSH25 and TSH50 diets gave the similar growth response. Fish fed diets TSH0, TSH75% and TSH100% showed reduced growth performance.