Growth, Feed Utilization, Survival and Fillet Nutrition Aspects of Asian Seabass (Lates calcarifer) Fed Diets with Shellfish and Fisheries Discards as Fish Meal Replacements

Abstract

Enhancing growth, survival and fillet qualities while lowering feed conversion ratio (FCR) and feed cost are considered crucial factors in aquaculture. Replacement of commercial fish meal (CFM) in fish feed with low-cost alternative protein sources has been in research focus for a long time. In the present study, the suitability of diets prepared using fisheries and shellfish wastes (FSW) as potential substitutes for CFM for Asian seabass was evaluated in a 121-day cage culture experiment conducted in a coastal lagoon of Sri Lanka. Five dry-pelleted diets were prepared to contain 40% of each main protein source, namely, dried filtrate of autolyzed prawn and crab wastes (Diet A), dried fish offal (Diet B), dried by-catch (Diet C), and 1:1 (w/w) mixture of dried offal and shellfish waste (Diet D), and CFM (reference Diet E). Pre-tested palatability of the five diets were in the same range. Absolute weight gain (WG), feed conversion ratio (FCR), protein efficiency ratio (PER), survival rate (SR), and fillet nutritive quality of seabass were compared among the five groups. Fish were graded into two size groups after 22 days to avoid cannibalism and the study was continued for another 99 days. Fish fed with Diet B had the highest WG (147.09 g), PER (1.73), highest survival (80%), and lowest FCR (1.61) with significantly higher crude protein (CP) level (41.74%), comparable crude fat (CF) (8.26%), highest levels of polyunsaturated fatty acids (PUFA) (27.33% of fat), n-3 PUFA (18.85% of fat) and omega-3/omega-6 ratio (2.22) in fillets. Fish fed with Diet C, D, and E had comparable WG, FCR, PER and CP in fillet. Although fish fed with Diet A had significantly lower WG (72.71 g), with CP (34.09%) and CF content (5.92%) in fillets compared to the fish fed with the reference diet, FCR (2.64) and PER (1.0) were not significantly different indicating that shellfish waste alone did not perform well on seabass nutritional quality. The present study revealed that fish offal waste in the test diet is the best alternative protein ingredient replacing CFM for seabass growout phase in cage culture without compromising the growth, feed utilization, and fillet nutritional quality, while by-catch and the autolyzed shellfish and fish offal mixture also have some potential to replace CFM in seabass diets.