Impacts of Protein-, L-Tryptophan-, Carbohydrate-, Oil-Rich Diets on Growth Performance, Levels of Melatonin, Oxidative Stress, Antioxidative Agents, and Vital Digestive Enzymes in the Gut of Juvenile Carp (Catla catla)

The dietary protein, tryptophan, carbohydrate, and oil content of fish feed has many vital roles in the growth performances, stress management, and digestive physiology of fish. However, in this context, the functions of gut melatonin, which depends on the availability of food, timing of food supply, frequency of feeds/day, quality of food, and growth stages of carp, still need to be clarified. The present study aimed to investigate the impact of different experimental diets on growth performances, melatonin, oxidative stress and its essential antioxidants in the gut, and vital digestive enzymes of juvenile carp, Catla catla (mean body weight ~50g). The fish were fed any one of the seven diets viz. (i) a standard diet (SD/control) (with 34.99% protein, 14.56% carbohydrate, 9.84% oil, and 0.36% L-tryptophan) (ii) two protein (PRD1 with 41.02%, and PRD2 with 50.55% protein), (iii) two L-tryptophan (TrpRD1 with 0.96%, and TrpRD2 with 1.36% tryptophan), (iv) one carbohydrate (CRD with 24.62% carbohydrate), and (v) one oil (ORD with 14.68% oil) - rich diets for 30 days. Results indicated that the growth performance was better in PRDs, TrpRDs, and CRD compared to SD but not in ORD-fed carp. Further, PRDs and TrpRDs stimulated gut melatonin and suppressed oxidative stress by enhancing all the studied antioxidant levels. Upregulated digestive enzyme activities were also recorded after the PRDs and TrpRDs supply. However, CRD and ORD-fed groups exhibit less/no impact on most studied parameters, except digestive physiology. Nonetheless, the current study reports for the first time that PRDs and TrpRDs can modulate gut melatonin, oxidative stress, different antioxidants, and digestive efficacy.