Effect of composite mixture of seafood by-products and soybean proteins in replacement of fishmeal on the performance of red sea bream, Pagrus major

Abstract

Feeding trials were conducted to evaluate the potentialities of using a mixture of different protein sources based on seafood by-products and soybean proteins to partially or completely replace fishmeal in practical diets for red sea bream, Pagrus major. Four diets (50% crude protein and 20kJg−1 gross energy) were formulated by replacing 0 (FM100), 60 (FM40), 80 (FM20) and 100% (FM0) of fishmeal with different proportions of sea food by-products and soybean proteins. A commercial diet (19.3kJg−1 gross energy) was used as the reference diet (COM). The growth trial was conducted with fifteen fish (average initial weight, 1.35g), stocked in triplicate in each of 15, 100-l polycarbonate circular tanks and fed all the test diets to apparent satiation by hand twice daily for 56days. After the growth trial, the remaining fish of each treatment were used to assess the apparent digestibility coefficients (ADCs). Dietary effects on heavy metal accumulation in fish fillets were evaluated by an independent feeding trial. Duplicate groups of fish (5.50g) were supplied FM100, FM20 and FM0 diets for 120days. A group of similar size red sea bream fed COM diet collected from a commercial farm in Nobeoka, Miyazaki, Japan was compared as a reference.Results of the study indicated that weight gain (%) and specific growth rate (% day−1) of fish were not differed significantly (P>0.05) with up to 80% fishmeal replacement. In this replacement level, growth of fish was also comparable (P>0.05) with those fed COM. Feed efficiency ratio and protein efficiency ratio were significantly (P<0.05) depressed in 100% fishmeal replacement group (FM0); however, no difference was found among the rest. Similar trends were also found for protein gain and retention. Whole body protein was comparatively higher and total lipid was significantly lower in the COM group. No difference was found in condition factor and hepatosomatic index among treatments. There was no abnormal sign in hematological parameters and oxidative stress condition of fish and it was assumed that all the fish were in good physiological state. The ADC of protein was significantly decreased in the FM0 group. Dietary treatments had no significant effects on the heavy metal accumulation in fish fillet after 120days. Based on the present experimental conditions, it has been concluded that 80% of the fishmeal in a typical commercial diet could be replaced with a combination of seafood by-products and soybean proteins while confirming performance and quality of red sea bream.