The study consisted of two experiments, Experiment 1, seclection of seafood processing by-products as protein sources in aquatic animal diets and Experiment 2, substitution of fish meal by seafood processing by-products in seabass cliets. in Experiment 1, tuna heads, tuna viscera and shrimp heads were processed as meal product and protein hydrolysate. Protein content and essential amino acid composition of tuna visceral meal and tuna visceral hydrolysate were higher (p<0.05) than those produced from tuna heads and shrimp heads. Tuna head meal gave maximum yield of 24.60% while tuna viscera gave the maximum yield of 20.10% for hydrolysate. In Experiment 2, three-factor factorial study consisted of types of by-products (tuna viscera and a mixture of tuna viscera and head), product types (meal and hydrolysate) and levels of substitutuion (0, 25, 50, 75 and 100%) was carried out. Twenty diets were formulated and fed twice daily until satiation to seabasswith and average initial weight of 3.25-3.38 g/fish for 10 weeks. Each treatment was composed of 3 replicates in flow-through system with continous aeration. The results showed that there was no interaction among types of by-products, product types and substitution levels an growth performance, feed intake, feed conversion ration (FCR), productive protein value (PPV) and surival rate. However, the interaction between product types and substtution levels was statistically significant (p<0.05). Regardless of by-products, final weight, weight gain and specific growth rate (SGR) of fish fed meal products and protein hydrolysate at 0 and 25% substitution was significantly higher than those at 50, 75 and 100% substitutuion. Besides, seabass fed 25% tuna visceral meal substitution diets had higher feed intake than those fed protein hydrolysate. Substitution at 100% resulted in the poorest growth performance and the highest FCR, PPV of fish fed diets containing a mixture of tuna viscera and tuna head at 75 and 100% substitution were signigicantly the lowest (p<0.05). The survival rate was not significantly different among treatments. The results of this study demontrated that tuna viscera and a mixture of viscera and head can be used to substitute 25% of fishmeal protein with good growth and feed util zation dffciency comparable to those fed fish meal based diets. Moreover, inclusion of tuna viscera at the stated level increases palatability of the diets.

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