In the present study, the influence of dietary FPH on feed utilization including feed efficiency, protein efficiency, and protein retention corresponded well with that on growth. Only very high levels of fish meal protein replacement by FPH protein reduced the feed utilization. The reduction of feed utilization by FPH could be due to the lower bioefficacy
values of free amino acids contained in protein hydrolysate, which is mainly resulted from the gastrointestinal absorption rate asynchronism between free amino acids and protein-bound amino acids. However,on the opposite side, high levels of dietary FPH increased the feed intake,
which offset its negative effects on feed utilization to some extent.The stimulatory effects of FPH on feeding have been demonstrated in previous studies on Atlantic salmon and Asian seabass . The enzymatic treatment of fish protein may cause formation of peptides with short
chain length that might act as an attractant for some species.