Effects of dietary melatonin on growth performance, nutrient composition, and lipid metabolism of Pacific white shrimp ( Penaeus vannamei)

The goal of this study was to investigate the effects of dietary melatonin (MT) on the growth physiology and lipid metabolism of Penaeus vannamei (P. vannamei). We prepared six experimental diets with varying MT levels (0 (control), 22.5, 41.2, 82.7, 165.1, 329.2 mg/kg) and fed six groups of shrimp with these diets for 2 months. The highest survival, body length growth rate, weight gain, and specific growth rates occurred in shrimp that were fed the diet containing 82.7 mg/kg MT, and the highest levels of docosahexaenoic acid (DHA) and arachidonic acid (ARA) were also found in this treatment group. Compared with the control group, there were no significant differences in moisture, crude protein, and ash contents in shrimp fed with MT, but the crude lipid content was significantly decreased in the high concentration MT supplemented group. Compared to the control group, shrimp fed 82.7 mg/kg MT had better morphology and structure of the hepatopancreas, whereas the hepatopancreas tissues were damaged in shrimp from the high dose MT groups. Analysis of lipid metabolism-related enzymes and genes in the hepatopancreas showed that dietary MT greatly decreased fatty acid synthase and acetyl-CoA carboxylase activities but increased carnitine palmitoyltransferase 1 activity. At the transcriptional level, dietary MT reduced hepatopancreas fat accumulation by upregulating lipid oxidation genes and downregulating lipid synthesis genes. A broken-line model revealed that the ideal MT concentration was in the range of 59.59-71.97 mg/kg. We found that MT supplementation improved P. vannamei growth performance, enhanced fatty acid beta oxidation, and prevented fat deposition in the hepatopancreas.