Dietary carbohydrate-to-lipid ratios influences muscle composition, metabolism, and liver histology in Tropical Gar (Atractosteus tropicus).

To determine the effect of dietary carbohydrate-to-lipid ratios (CHO/L) on growth performance, digestive enzyme activity, muscle composition, liver morphology and metabolic key gene expression in tropical gar (Atractosteus tropicus) a completely randomized design was conducted. Five diets were designed with different CHO/L ratio (D1: 1.03, D2: 1.52, D3: 2.17, D4: 2.74, D5: 4.3) and supplied to fish with initial weight of 23.4 ± 1.1 g for 45 days. Growth performance parameters, survival, proteases and amylases activities were similar between treatments and control, while lipases had higher activity in D5 group. The muscle composition of fish fed D5 showed better protein assimilation compared to the control, with a protein content of 83.7% and 5.5% lipids. Although blood glucose increased in fish receiving carbohydrate rich diets, the upregulation of key metabolic genes indicated that excess glucose was redirected toward lipogenesis to maintain homeostasis. Histological analyses revealed hepatocyte hypertrophy, vacuolization and morphological alterations in the liver as dietary carbohydrates increased. Results suggest that A. tropicus juvenile are capable to assimilate diets with 4.3 CHO/L ratio, in addition to improving the protein utilization.