NUTRITIONALLY BALANCED, COST-EFFECTIVE FEED  FORMULATION FOR ASIAN SEABASS (Lates calcarifer) 

High-cost feed is the major concern in culturing Asian seabass (Lates calcarifer) in Sri Lanka. Commercial fish meal (CFM) is the most expensive ingredient in fish diet. Being a carnivore, over 40% of dietary protein content is required forn optimum growth of seabass. The objective of the present study was to evaluate the possibility of replacing the CFM fully  with alternative main protein sources (AMPS), namely, shellfish waste (dried filtrate of autolyzed prawn and crab waste), fishn offal, and by-catch (Kelee shad) in seabass feeds without compromising nutritional aspects. Four test feeds containing different AMPS (40% by weight), i.e., shellfish waste (A), fish offal (B), by-catch (C), a mixture (1:1) of dried offal, shellfish waste (D) were prepared. The reference diet (E) had CFM as the main protein source. Other ingredients (60%) were common to all feeds. Seabass fingerlings (55 days old) were stocked in floating cages (in triplicate, 50 per cage) and hand-fed until visual satiation. The length and weight of 30% of caged fish were measured fortnightly. After 22 days, fish were graded into two size groups to avoid cannibalism. After 99 days further, total weight of each fish was recorded, and weight gain (WG), specific growth rate (SGR), feed  conversion ratio (FCR), protein efficiency ratio (PER), and survival rate (SR) were calculated. Proximate composition of AMPS, formulated feeds and fish fillets of cultured  fish and their wild counterparts were carried out using standard procedures. Organoleptic  qualities of fish fillets of cultured seabass and wild seabass were assessed on a 7-point hedonic scale. Crude protein (CP) content of AMPS was not significantly different from  CFM except for fish offal. Crude fat (CF), n-6 fatty acids, and polyunsaturated fatty acids (PUFA) of the test feeds were not significantly different from those of the reference diet.  Diet E and Diet D had significantly higher levels of essential amino acids and n-3 fatty acids compared to other formulated feeds. Diet B had the highest values for all growth indices, the  lowest formulating costs, and the lowest FCR. Fish fed with Diet D showed similar WG, SGR, PER, and FCR compared to the fish fed Diet E, whereas Diets A and C produced  significantly lower growth performance. Fillets of fish fed Diets B and D had significantly higher levels of CP and CF compared to that of fish fed Diet E and wild seabass. Fillets of  fish fed with Diets B and D showed similar levels of PUFA, n-3 fatty acids, n 3/n-6 ratio as Diet E and wild seabass. Organoleptic qualities of fillets of caged fish and wild counterparts  were not significantly different. The study concluded that fish offal is the most suitable and low-cost AMPS for culturing both fingerlings and the grow-out stage seabass.

Keywords: Asian seabass, cage culture, fish feed, fisheries by-products, fillet organoleptic 
qualities