Effects of feeding regimes and dietary energy on the production performance, plasma immune parameters and expression of genes involved in the TOR/S6K1 pathway of juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Abstract

The aim of this research was to assess the effects of different feeding regimes on growth performance, plasma immune indices and related genes' expression of hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) juveniles fed two dietary energy levels. A 3 × 2 factorial experiment was designed including three feeding regimes (two meals a day, one meal a day, one meal every two days; designated as 2 M, 1 M, 2DM) and two dietary available energy levels (3.4 and 3.6 kcal/g; designated as E3.4, E3.6), with three replicates per treatment. Juvenile hybrid grouper (average initial body weight: 19.39 ± 0.04 g/fish) were cultured for 6 weeks in 18 floating cages (125 cm × 80 cm × 40 cm) placed in six concrete ponds sharing the same water source. Results revealed that the 2 M and 1 M treatments had significantly higher weight gain rate (WGR), protein efficiency ratio (PER), expression of hepatic IGF-1, TOR, and S6K1 than the 2DM treatment (P < 0.05), whereas feed conversion ratio (FCR) displayed an opposite trend (P < 0.05). No significant differences in the above parameters were found between the 2 M and 1 M groups. As the feeding frequency decreased, the total feed intake (FI) per fish was significantly reduced (P < 0.05), while feed intake per meal (FIM), stomachic index (SI) and expression of hypothalamus agouti related neuropeptide (AgRP) were significantly increased (P < 0.05). The 2 M treatment supported higher plasma lysozyme contents than the 1 M and 2DM treatments (P < 0.05). The E3.6 treatment had higher intraperitoneal fat ratio and intestinosomatic index, but lower plasma lysozyme and immunoglobulin M contents than the E3.4 treatment (P < 0.05). Based on our results, a feeding regime of two meals/day of a diet containing 3.4 kcal DE/g of dry matter is recommended for the culture of juvenile hybrid grouper with an initial size of 19.39 g.