Abstract:The effects of five different feeding frequencies on the growth performance, physiological index, and hepatic heat shock protein 70 (hsp70) gene expression levels of juvenile Thamnaconus septentrionalis [body weight of (6.47±0.56) g] were studied. The experiment design included 5 feeding frequencies, namely 1, 2, 3, 4, and 5 times/d (referred to as F1, F2, F3, F4, and F5 respectively), and each treatment group was designed with 3 parallels, and each tank was cultured 30 fish. The experimental period was 30 days and water temperature range was 17℃~26℃, the salinity was 30~31, the pH was 6.8~7.6, and the dissolved oxygen was ≥ 5 mg/L. Results showed that under different feeding frequency conditions, the growth, body composition, digestive enzymes, and antioxidant enzyme activities of the juvenile T. septentrionalis were affected. With the increase in feeding frequency, the feeding and growth of T. septentrionalis showed an upward trend. The F5 group had the largest value, with a feeding rate of 3.95%, a weight gain rate of 347.19%, a specific growth rate of 5.07%/d. The weight gain rate of the F5 group exceeded twice the value of the F1 group. The condition factor of the F1 group was 1.79, which was significantly lower than that of the other four groups (P<0.05). The hepatosomatic index gradually increased, and the F4 and F5 groups exhibiting significantly higher values than the other three groups (P<0.05). With an increase in the feeding frequency, the crude protein content of the experimental fish showed a trend of first increasing and then decreasing: F2 showed the highest crude protein content of 59.82%, and the crude lipid content showed a gradually increasing trend: F5 was the highest with a crude lipid content of 31.23%. Trypsin activity showed a trend of first decreasing and then increasing with the increase in feeding frequency. The F3 group had the lowest activity of 37.48 U/μg prot; lipase activity gradually increased, and the F5 group showed the highest activity of 2.67 U/g prot; amylase activity was not affected by the feeding frequency (P>0.05). Catalase activity, superoxide dismutase activity, and the content of malondialdehyde were the highest in the F5 group, at 14.71 U/mg prot, 250.32 U/mg prot, and 2.73 nmol/mg, respectively. The relative expression levels of the hsp70 gene in the liver was not affected by the feeding frequency (P>0.05). Based the findings of this study and the comprehensive consideration of the growth performance and physiological indices of Thamnaconus septentrionalis, the optimal feeding frequency for this species was determined to be 3 times/d.
