Growth performance and enzymatic activities in monosex tilapia (<scp><i>Oreochromis niloticus</i></scp>) supplemented with <scp><i>Najas indica</i></scp> along with the compound identification of the extracts

Recent research has looked at various macroalgae species as dietary components or feed additives for a variety of fish species due to their nutritional value. The objective of this study was to examine the impact of Najas indica, a macroalgae extract, on the growth performance, proximate composition, and metabolic activities of monosex tilapia (Oreochromis niloticus), while also isolating the compounds present. Three distinct solvents (n-hexane, ethyl acetate, and ethanol) were used to extract bioactive compounds from a coarse powder of macroalgae after drying and grinding, and gas chromatography-mass spectrometry (GC-MS) analysis was used to detect bioactive compounds. The extracts were combined with commercial feed (0.4%) and applied to the treatment with three replications and a control containing 50 fingerlings per tank for 5 weeks. The findings indicated a significant increase in the final weight, weight gain, specific growth rate (SGR), and survival rate among the treated fish, whereas the feed conversion ratio (FCR) was observed to decrease in comparison to the control group. Significantly higher levels of protein and lipids were found in treated fish, whereas moisture and ash levels were significantly lower compared to control fish. In treated fish, the digestive enzyme amylase was significantly higher, but the protease enzyme reduced significantly. The antioxidant enzyme superoxide dismutase activity (SOD) was significantly higher in the treatment group, whereas the catalase (CAT) enzyme did not differ significantly. A total of 47 bioactive compounds were identified in N. indica, among which the prominent compounds included n-hexadecanoic acid, neophytadiene, phytyl palmitate, d-mannitol, and heptanoic acid. The results obtained from this study indicate that the utilization of N. indica macroalgae extract has the potential to serve as an additional dietary component, therefore, enhancing the growth performance and metabolic functions of fish.