Comparative study of carbohydrate levels on growth, oxidative stress and glucolipid metabolism of hybrid fish between Megalobrama amblycephala (♀) × Culter alburnus (♂) and Culter alburnus

The present study used hybrid fish (Megalobrama amblycephala ♀ × Culter alburnus ♂, abbreviated as BT) and topmouth culter (Culter alburnus, abbreviated as TC) as research subjects to assess and compare the effects of carbohydrate on the growth, oxidative stress and glucolipid metabolism of the two fish. The TC (initial weight, 13.10 ± 0.10 g) and BT (initial weight, 12.85 ± 0.13 g) were fed isonitrogenous (43% crude protein) and isolipidic (6.5% crude lipid) diets with carbohydrate levels of 10% (LC diet) and 30% (HC diet) for 11 weeks, respectively. The results showed that the HC diet resulted in a significant decrease in specific growth rate (SGR) of both fish. However, the SGR in BT was significantly higher than in TC, regardless of diet. Furthermore, HC diet significantly increased serum alanine transaminase (GPT) and hepatic malondialdehyde (MDA) content, decreased hepatic catalase (CAT) activity and resulted in increased hepatocyte volume, nucleus deficiency and nucleus deviation from the center of cytoplasm in both fish. However, BT had significantly higher glutathione peroxidase (GPx) activity and lower serum GPT and aspartate transaminase (GOT) content compared to TC. The HC diet induced significant increases in hepatosomatic index (HSI), liver lipid droplet area, liver glycogen, serum glucose (GLU) and triglyceride (TG) content in both fish. However, HSI and lipid droplet area were significantly higher in BT than in TC, while serum GLU and TG content were significantly lower in BT than in TC. Both fish can adapt to the HC diet by up-regulating the expression of glycolysis-related gene (glucokinase (gk)) and lipogenesis-related genes (acetyl-CoA carboxylase a (acca), fatty acid synthase (fas)). However, the expression levels of glucose transporter 2 (glut2), glycolysis-related gene (phosphofructokinase liver b (pfklb)) and lipogenesis-related genes (sterol regulatory element-binding protein 1 (srebp1), ATP citrate lyase a (aclya)) were increased only in BT fed HC diet. In summary, the BT liver has stronger glucose transport, glycolysis, and lipid tolerance compared to TC, thus exhibiting better glucose homeostasis and growth performance. It indicates that hybridization may help to produce new strain of fish with high carbohydrate utilization capacity.