Exercise training promotes growth through hypertrophy and enhances capillarization and antioxidant capacity in juvenile largemouth bass (Micropterus salmoides)

Exercise training can improve the growth performance, immunocompetence, and stress resistance of fish, even altering their physiological parameters and gene expression. Largemouth bass (Micropterus salmoides) that originally lived in rivers and lakes are now often raised in ponds without flowing water, leading to a lack of exercise. This study examined the effects of exercise training on largemouth bass (with initial body length 10.68 +/- 0.32 cm) growth performance by analyzing white muscle microanatomy and angiogenesis and by measuring antioxidant capacity in muscle and liver. Three water velocities were employed to assess the effects for 60 days: V0 (0 cm/s, control), V1 (13.4 +/- 0.4 cm/s), and V2 (26.5 +/- 0.9 cm/s). The results showed that: (1) both exercise groups had higher feeding rates, and group V1 exercised fish showed significant increases in weight gain, specific growth rate, and final body length. (2) Exercise training promoted muscle hypertrophy by increasing fiber cross-sectional area in the group V1. The expression levels of growth-related genes such as insulin-like growth factor-1 (IGF-1), mammalian target of rapamycin (mTOR), and ribosomal protein S6 kinase beta 1 (S6K1 beta) were upregulated, accompanied by inhibition of growth in the group V2 via upregulation of the expression of muscle ring protein 1 (MuRF1) and atrogin-1. (3) Exercise training significantly promoted angiogenesis processes, and the expression of angiogenesis-related genes such as vascular endothelial growth factor A (VEGF-A) and its receptor VEGFR2 was upregulated in liver and muscle. (4) Exercise training reduced the risk of oxidative stress in liver and muscle by increasing antioxidant enzyme activity in the group V1; however, fish in the group V2 had decreased antioxidant enzyme activity and increased malondialdehyde (MDA) and reactive oxygen species (ROS) contents in muscle and thus may have been at risk of oxidative stress. In conclusion, exercise training with an appropriate water flow velocity can stimulate the growth potential of largemouth bass through muscle hypertrophy and enhance capillarization and antioxidant capacity.