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 20 kJ g−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 (19.3 kJ g−1 gross energy) was used as the reference
diet (COM). The growth trial was conducted with fifteen fish (average initial weight, 1.35 g), 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 56 days. 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 (5.50 g) were supplied FM100, FM20 and FM0 diets for 120 days.
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 (Pb0.05) 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 120 days. 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