Dietary clenbuterol modifies the expression of genes involved in the regulation of lipid metabolism and growth in the liver, skeletal muscle, and adipose tissue of Nile tilapia ( Oreochromis niloticus )

The current study aimed to evaluate whether clenbuterol, a beta(2)-adrenergic agonist, supplementation in Nile tilapia (Oreochromis niloticus) diets can influence growth and blood parameters. Besides, assessment of adipo- genic genes as fatty acid synthase (FAS ) and lipoprotein lipase (LPL ) which is a key enzyme in the regulation of the flux of fatty acids in liver, muscle, and adipose tissue as well as muscle growth -regulating genes as myostatin (MYO ) in muscle and insulin -like growth factor -1 (IGF-1 ) in liver. The fish were allocated into three equal groups; control group that fed basal diet only and the other two groups fed a basal diet containing clenbuterol at two doses 5 ppm and 10 ppm/kg diet for 30 consecutive days. Results revealed that clenbuterol supplementation significantly increased body weight, decreased liver, spleen and abdominal fat weights, and decreased total circulatory cholesterol and triacylglycerol levels. Moreover, clenbuterol inhibits lipogenesis by downregulation of FAS gene expression by dose and time -dependent manner in the liver while enhanced lipolysis in both the liver and in the adipose tissue. Moreover, lipolysis was reduced in muscle by dose 10 ppm on day 30. Furthermore, clenbuterol presented higher gene expression of MYO and IGF-1 in muscle and liver respectively by dose 5 ppm at day 15 on the other hand, these findings were reversed by day 30 compared with control. In conclusion, clenbuterol efficacy was apparent in a dose and time response pattern to boost growth and reduce fat deposition rates, indicating for the first time that clenbuterol has a profitable growth impact on Nile tilapia.