Abstract:Golden pompano Trachinotus ovatus is one of the most commercially important carnivorous marine species cultured in China. In recent years, the large-scale development of the aquaculture industry of T. ovatus has been rapid because of its fast growth rate and high flesh quality, and annual output has exceeded 100 000 tons. Currently, commercial formula feed for this fish still contains over 20%~30% of fishmeal (FM), the use of which precludes a sustainable aquaculture industry. As an alternative protein source, terrestrial compound proteins, which are a combination of several easily available and relatively low-priced terrestrial animal proteins and enzymatic hydrolysis or fermentation of terrestrial plant protein in a certain proportion, can alleviate the amino acid imbalance caused by a single alternative source. Terrestrial compound proteins are known to reduce the use of FM in marine carnivorous fish diets. In addition, fish protein hydrolysate is a new protein source that is processed from fish catches. In contrast to fish meal, it has an essential enzymatic hydrolysis step in the production process, so it contains more oligopeptides and free amino acids, which has been widely concerned in the industry. However, there are no reports on the application of fish protein hydrolysate in the feed of golden pompano. In order to decrease the use of FM in T. ovatus diets and evaluate the feasibility of substitution by terrestrial compound proteins and fish protein hydrolysate, this study was conducted to investigate the effects of replacing FM with compound protein and fish protein hydrolysate on growth performance, serum biochemical indexes, digestive enzyme activity, and tissue antioxidant capacity of T. ovatus. Four diets containing 42% crude protein and 12% crude fat were formulated, including D1 (control group), containing 30% fish meal; D2~D4 containing 14% terrestrial compound protein, 16%, 11%, and 6% fish meal, and 0%, 5%, and 10% fish protein hydrolysate, respectively. Methionine and lysine were added to the D2~D4 groups. T. ovatus juveniles (approximately 4 g mean initial weight) were bought from a local fish farm and then maintained for 2 months in two sea cages (2.0 m × 2.0 m × 2.0 m) at the coast near Nanao Marine Biology Station of Shantou University. A total of 360 fish (average body weight: [(7.28±0.10)g] were randomly distributed into 12 cages (1.0 m × 1.0 m × 1.5 m) and fed one of the four diets for 62 d. During the 62-d feeding trial, fish were fed to apparent satiation twice daily at 6:00 and 17:00, and the seawater temperature was 26.9℃~33.3℃, salinity was 27~33. The dead fish were collected over time and the day of death recorded. There were no significant differences in weight gain rate, specific growth rate, protein efficiency rate, feed conversion, feed rate, hepatosomatic index, viscerosomatic index, and condition factor, as well as pepsin, lipase, and amylase activity among all treatment groups (P>0.05). The whole-body protein content of groups D3 and D4 was significantly higher than those of groups D1 and D2 (P<0.05), and muscle fat content of groups D1~D3 was significantly higher than that of group D4 (P<0.05). The activity rate of aspartate aminotransferase in groups D2~D4 and alanine aminotransferase in groups D2 and D3 were significantly lower than those in group D1 (P<0.05). Total protein and globulin levels of groups D1 and D4 were significantly higher than those of groups D2 and D3 (P<0.05). Liver catalase activity, total antioxidant capacity, and muscle superoxide dismutase activity of groups D2~D4 were significantly higher than those of group D1 (P<0.05), but liver malondialdehyde content in groups D2~D4 was lower than that of group D1 (P<0.05). Overall, the whole-body protein content and tissue (liver and muscle) antioxidant capacity of group D4 were significantly higher than those of other groups, and no significant differences in growth performance were found between groups D4 and D1. The use of fish protein hydrolysate increased the level of protein metabolism and immune function of the fish and reduced the degree of liver cell damage. The results indicate that 14% terrestrial compound protein combined with 10% fish protein hydrolysate can effectively replace 80% fish meal in the diet of golden pompano when the amount of fish meal is reduced to 6%. This study is the first to investigate the feasibility of the application of fish protein hydrolysate in the formula feed of golden pompano, and the results will be relevant to the research for high-quality and inexpensive protein sources in the artificial formula feed of juvenile golden pompano.
