Evaluation of High Efficiency and Low Fish Meal Diets for Golden Pompano (Trachinotus ovatus) in Deep-Sea Cage Culture

Trachinotus ovatus, commonly known as golden pompano, is a euryhaline warm water carnivorous fish. It has the characteristics of fast growth, simple feeding, delicious meat, strong stress resistance, and high survival rate. It can accept compound feed throughout its growth. It is popular among fish breeders and consumers because of its moderate specifications and affordable price. With an annual output of 240 000 tons, it has become one of the most important marine fish breeding species in the southern coastal areas of China. As a marine carnivorous fish, it has specific requirements relating to the levels and sources of dietary protein and fat, and a strong dependence on fish meal and fish oil, which are limited resources with high prices, which also determines its high feed cost. However, compared with other rare sea fish, its price is low and the profit margin of breeding is low (2–4 CNY/kg), thus, easily leading to the loss of breeding enterprises and individual businesses. Therefore, it is necessary to develop efficient and low-cost compound diets and reduce the supplemental level of fish meal oil in diets to solve the bottleneck problem of golden pompano fish breeding. Previous studies have shown that T. ovatus subjected to a high efficiency and low fish meal diet exhibited excellent growth and health in pond cage culture. To further evaluate the application effect of this feed in deep-sea cage culture, an experimental feed (crude protein 47.66%, crude fat 7.98%) based on the formula feed of a low fish meal diet was produced by a feed company with a large-scale production process (feed production using large machinery and mass production in a feed mill with an hourly output that can reach more than 10 t using equipment such as oil sprayer machines, where the fat source is added by spraying). A commercial feed from a well-known brand was used as the control diet (crude protein 47.75%, crude fat 9.63%). Large-sized golden pompano (mean body weight ~262 g) were provided by Yangjiang Haina Fisheries Limited and kept for 2 weeks at the deep-sea cage breeding base in Dasuo Island, Yangjiang (12–20 m depth, about 15 km offshore) to adapt to the test environment. During the temporary feeding period, a well-known commodity was used for feed. Overall, 150 000 healthy large-sized golden pompano with neat specifications (initial body weight ~260 g) were selected and randomly assigned to six deep-sea cages (HDPE C60 floating cages, circumference 60 m, 25 000 fish per cage). Each feed was provided in three parallel cages for 33 days (April 29 to May 31, 2021). During breeding, full food was provided twice a day (07:00 and 17:00). During the experiment, the seawater temperature was 20.00~29.00 ℃. Dissolved oxygen was 6.30~7.80 mg/L. The results showed that the growth performance of fish was not statistically different between the two groups (P > 0.05). However, compared with the control group, the weight gain rate and specific growth rate of fish-fed experimental diets increased by 14.43 % and 8.19 %, respectively, and the average daily weight gain increased by 0.68 g. In terms of muscle nutrition and texture characteristics, the muscle lipid contents of the fish-fed experimental diets were significantly higher than those of fish-fed control diets (P < 0.05), but the muscle moisture content significantly decreased (P < 0.05). The edible quality and texture characteristics of muscle were comparable between the two groups (P > 0.05). Compared with the control group, the serum protein, triglyceride, total cholesterol, and low-density lipoprotein contents, as well as the activity of aspartate aminotransferase, of fish fed the experimental diet were significantly decreased (P < 0.05), and the hepatic total cholesterol content of the experimental group was significantly decreased (P < 0.05). There was no significant difference in liver antioxidant capacity between the two groups (P > 0.05). In addition, the feed cost per 1 kg of fish receiving the experimental diet was 18.80% lower than that of fish receiving the control diets, and its culture benefit was increased by 62.12%. The results showed that the experimental diet (high efficiency and low fish meal diet) not only promoted growth, but also improved the muscle fat level and serum lipid metabolism of the fish. These results indicate that the high efficiency and low fish meal diet can be applied in the culture of golden pompano within deep-sea cages. In this study, a high efficiency and low fish meal diet for T. ovatus was developed by using amino acid balance technology and fatty acid precision nutrition technology in deep-sea cage large-scale culture. Through the analysis of growth performance, serum biochemical parameters, liver lipid metabolism, and antioxidant properties, it was found that the growth promoting effect of test material was comparable to that of commercial material, and could improve the muscle quality and liver health of golden pompano. Use of the experimental diet could also reduce the cost of breeding, improve the economic benefits, and result in high economic value. The results indicate that the experimental high efficiency and low fish meal diet for T. ovatus has a good application effect and excellent market development prospects, and also has important practical guiding significance for the large-scale production and application of high efficiency low fish meal compound feed, solving the problem of aquaculture bottleneck and facilitating deep-sea golden pompano culture.