Sustained exercise improves growth performance and reduces fat deposition in gilthead sea bream juveniles fed with a high-protein and a high-carbohydrate diet

In gilthead sea bream, sustained exercise induces metabolic and endocrine adaptations towards more efficient dietary nutrients use and better growth performance. This work aims to examine in this species the combined effects of swimming activity (voluntary swimming vs. exercise) and diet composition (high-protein diet vs. high-carbohydrate diet) on growth performance, muscle composition, flesh texture, and gene expression of growth hormone (Gh)/insulin-like growth factors (Igfs) axis members and muscle development markers. After 6 weeks of experiment, fish subjected to sustained exercise exhibited enhanced growth performance and reduced muscle lipid content, mesenteric fat and hepatosomatic index compared to those in voluntary swimming. Also, exercised fish fed with the high-protein diet showed the highest final body weight. Unexpectedly, exercise appeared to reduce flesh texture parameters, mainly elasticity. Regarding the gene expression, the hepatic levels of the anabolic Gh receptor (ghr-1) were significantly higher in the exercised fish fed with the high-protein diet compared to other groups. The high-protein diet increased the gene expression of different molecules of the Gh/Igfs axis in liver (igf-1, igf-2, igfbp-2, igfbp-4, igfbp-5, igf-1rb, akt-2) and akt-2 in muscle, suggesting a better anabolic endocrine state. In muscle, the proteolytic systems gene expression was not affected by either swimming activity or diet composition, but the high-protein diet upregulated the transcription of myogenic and proliferative markers like pcna, myf5 and myod2. Overall, these results highlight the positive effects of exercise on growth performance and lipid reserves utilization in gilthead sea bream juveniles, suggesting exercise as a valuable tool when formulating protein-adjusted diets for this species.