Effects of Formulated Diet and Frozen Fresh Fish on Growth, Serum Biochemical Indexes, Liver Antioxidant, and Lipid Metabolism of Juvenile Cobia (Rachycentron canadum)

Abstract

Feed is the main source of material and energy for farmed fish, and its nutritional value and balance are important factors affecting fish’s growth rate and physical health. In order to explore the effects of two different feed sources on the growth, serum biochemical indexes, liver antioxidant capacity, and lipid metabolism of young cobia fish, 300 young cobia fish with an initial body weight of 43.14 ± 1.25 g were selected for the experiment and randomly divided into two treatments. Each treatment had five replicates, and each replicate had 30 fish. They were fed with formulated feed and frozen fresh fish, respectively, for 12 weeks. The results showed that the weight gain rate, specific growth rate, and feed conversion rate of juvenile cobia fish fed with formulated diet were extremely significantly lower than those of the frozen fresh fish group ( $P<0.01$ ), and condition factor was significantly lower than that of the frozen fresh fish group ( $P<0.05$ ). However, protein efficiency rate, hepatosomatic index, and viscerosomatic index were significantly higher than those of frozen fresh fish group ( $P<0.05$ ). The content of water, crude protein, and crude ash in the whole fish had no significant difference ( $P>0.05$ ), while the content of crude lipid decreased significantly ( $P<0.05$ ). The serum aspartate aminotransferase activity and sugar content of cobia in the formulated diet group were significantly higher than those in the frozen fresh fish group ( $P<0.05$ ). In contrast, the total cholesterol, triglyceride content, alkaline phosphatase activity, and phosphorus content were significantly lower than those in the frozen fresh fish group ( $P<0.05$ ). Compared with the frozen fresh fish group, the antioxidant enzyme activities in the liver of the formulated diet group were significantly decreased ( $P<0.05$ ) except malondialdehyde (MDA) and the activity of fatty acid synthase, while there was no significant difference in the malate dehydrogenase. The study showed that under the experimental conditions, frozen fresh fish was more suitable for feeding juvenile cobia, and the formulated diet had adverse effects on the liver of juvenile cobia. Therefore, the nutritional composition of frozen fresh fish and the metabolic characteristics of cobia were used for reference to optimize and adjust the nutritional formula of juvenile cobia.