Impacts of Amla (Phyllanthus emblica) fruit extract on growth, skin mucosal and serum immunities, and disease resistance of Nile tilapia (Oreochromis niloticus) raised under biofloc system

This study aimed to investigate the effects of Amla (Phyllanthus emblica) fruit extract (AFE) on the growth, skin mucosal and serum immunity, and disease resistance of Nile tilapia (Oreochromis niloticus) against Streptococcus agalactiae. Three hundred fish (10.48 +/- 0.56 g fish-1) were distributed in 15 tanks with 20 fish per tank and fed basal diet supplemented with 0, 5, 10, 20, and 40 mg kg-1 AFE for eight weeks. The completed randomized design with three replications was applied. Growth performance, peroxidase, alternative complement, phagocytosis, and respiratory burst activities were determined at weeks 4 and 8. The challenge study was conducted at the end of the experiment. Based on the results, Nile tilapia fed the AFE diets significantly enhanced skin mucus lysozyme and peroxidase activities (P < 0.05) post-feeding. The highest levels were observed in the group that received 20 mg kg-1 of AFE (P < 0.05), whereas the control group presented the lowest levels of lysosome and peroxidase activities. Similarly, incorporation of 20 mg kg-1 of AFE brought about the maximum levels of (P < 0.05) serum lysozyme, peroxidase, alternative complement, phagocytosis, and respiratory burst activities in contrast to the other treatments; whereas fish fed the control diet generated the lowest immune parameter values (P < 0.05). In the challenge study, the Nile tilapia's relative percent survival (RPS) was 52.38%, 61.90%, 80.95%, and 47.62% in Diet 2, Diet 3, Diet 4, and Diet 5, respectively. Fish fed 20 mg kg-1 AFE showed significantly (P < 0.05) higher RPS, as well as the highest resistance towards S. agalactiae. The inclusion of AFE for 8 weeks resulted in a significant (P < 0.05) enhancement of growth parameters, with the highest growth rate observed in the 20 mg kg-1 AFE group. In conclusion, dietary supplementation with 20 mg AFE kg-1 may be used as a growth promoter and immunostimulant in Nile tilapia aquaculture.