Abstract:This experiment was to investigate the effects of fish protein hydrolysate on growth, feed utilization, body composition, and morphological structure of muscle fibers in turbot (Scophthalmus maximus L.). Six isonitrogenous and isolipidic diets were formulated and fed to fish. The experimental diets contained two control groups with no fish protein hydrolysate, positive control group including 44% fish meal, negative control group including 22% fish meal. Four experimental groups with different levels of fish protein hydrolysate and fish meal, PH4.5A group contained 22% fish meal and 4.5% fish protein hydrolysate, PH4.5B group contained 17% fish meal and 4.5% fish protein hydrolysate, PH18A group contained 22% fish meal and 18% fish protein hydrolysate, and PH18B group contained 0.5% fish meal and 18% fish protein hydrolysate. The results showed that there were no significant differences in the weight gain rate and specific growth rate between PH4.5A and PH18B groups (P>0.05), while PH4.5A group and PH18B group were significantly higher than that of PH4.5B group and negative control group (P<0.05) and significantly lower than that of PH18A and positive control groups (P<0.05). There were no significant differences in the feed efficiency, protein efficiency and protein retention efficiency between PH18A and positive control groups (P>0.05), while PH18A and positive control groups were significantly higher than that of PH18B, PH4.5A and negative control group (P<0.05). Contrary to feed efficiency, there were no significant differences in the feed intake among PH18A，PH18B and positive control groups (P>0.05), while these groups were significantly lower than that of PH4.5A, PH4.5B and negative control groups (P<0.05). There were no differences in the contents of crude protein and crude lipid between PH4.5B and negative control groups (P>0.05), while these groups were significantly lower than that of PH18A and positive control groups (P<0.05). There were no significant differences in total amino acids, essential amino acids and non-essential amino acids in the muscles among six groups (P>0.05). The muscle fiber cross-sectional area in PH18A group was significantly higher than that of PH18B, positive control, PH4.5A, negative control, PH4.5B groups (P<0.05), and PH18B group was significantly higher than PH4.5B group (P<0.05). The muscle fiber density of PH18A group and PH18B group was significantly lower than that of PH4.5B group (P<0.05). The above results show that both 18% and 4.5% fish protein hydrolysate added to high plant protein feeds can promote the growth of turbot and increase the feed efficiency and protein deposition rate of turbot, and growth and feed utilization in fish given 18% fish protein hydrolysate diet showed better than that of fish given 4.5% fish protein hydrolysate diets. For the morphological structure of muscle fiber, 18% fish protein hydrolysate in diets can increase the cross-sectional area of muscle fiber and reduce the muscle fiber density, while 4.5% of the fish protein hydrolysate did not affect significantly the cross-sectional area of the muscle fiber and the fiber density.
