Use of some agricultural by-products as functional feed additives for nile tilapia culture under biofloc system

Abstract

Nile tilapia (Oreochromis niloticus) is one of the most widely farmed fish due to its well-adapted fish, rapid growth, and significant commercial price. However, intensified aquaculture affects fish behavior, immunological function, and stress. Additionally, fish farming at high stocking density can give rise to the emergence of diseases and high accumulation of organic matters because of feed and faeces. Disease management in Nile tilapia aquaculture frequently involves the use of antibiotics and chemotherapy. Numerous plant-based immunostimulants or their derivatives continue to be the best alternative for avoiding the issues of drug residues and drug-resistant microbes in fish farming. The objective of this work was to evaluate the effects of mango peels and passion fruit peels on growth performance, mucosal and serum immunity, and relative immune and antioxidant gene expressions of Nile tilapia, Oreochromis niloticus. Mango peel experiment The effects of mango peel powder (MGPP) on growth, innate immunity, and immune-antioxidant related gene expression of Nile tilapia reared under biofloc system were investigated. Three hundred Nile tilapia (average weight 14.78 ± 0.05 g) were distributed into 15 fiber tanks (300 L per tank) assigned to five treatments in triplication. Fish were fed basal diet containing different levels MGPP as follows: 0 (MGPP0: control), 6.25 (MGPP 6.25), 12.5 (MGPP 12.5), 25 (MGPP 25), and 50 (MGPP 50) g kg−1 diet for 8 weeks. Specific growth rate (SGR), weight gain (WG), final weight (FW), feed conversion ratio (FCR), skin mucus of lysozyme (SMLA), and peroxidase activities (SMPA), serum of lysozyme (SL) and peroxidase (SP) were measured every four weeks; while immune- antioxidant-related gene expressions were determined after 8 weeks post-feeding. The results indicated that MGPP 25 diet resulted in higher SGR, WG, FW, and FCR but no significant differences among treatments were noticed. In terms of immune responses, lysozyme and peroxidase activities in mucus and serum were significantly higher in MGPP 12.5 and MGPP 25 diets against the control. Similarly, significant up-regulation of IL-1 and IL-8 gene expressions was observed in fish fed MGPP 25 against the control. However, no significant differences in LBP, GSTa, GPX, and GSR among treatments were observed. In conclusions, dietary inclusion of MGPP 25 significantly enhanced immune response and immune related gene expressions but not growth performance and antioxidant gene expressions. The results implied that MGPP can be potentially used as an immunostimulants in Nile tilapia culture. Passion fruit experiment The impacts of dietary supplementation with passion fruit (Passiflora edulis) peel powder (PSPP) on the growth, immune response, and expression of immune and antioxidant-related genes in Nile tilapia maintained in a biofloc system were examined. Fish were fed basal diets supplemented with different doses of PSPP at 10 g kg−1 (PSPP10), 20 g kg−1 (PSPP20), 40 g kg−1 (PSPP40), and 80 g kg−1 (PSPP80). The basal diet, without PSPP-supplementation, was used as a control at 0 g kg−1 (PSPP0). The results showed that the dietary supplementation groups fed different levels of PSPP exhibited no substantial difference or only slight increases in growth performance and immunological response in Nile tilapia (P > 0.05), whereas fish fed diets supplemented with PSPP at concentrations of 10 g kg−1 , 20 g kg−1 , and 40 g kg−1 had significantly higher mRNA transcripts (approximately 1.5–4.5 fold) of immune (IL-1, IL -8, and LBP) and antioxidant (GSTa, GPX, and GSR) gene expressions than fish in the control treatment group (0 g kg−1). In conclusion, these findings suggest that dietary supplementation with PSPP may effectively stimulate the immune and antioxidant defense system and may function as feed additives in Nile tilapia cultured in a biofloc system. Overall, dietary inclusion of mango peel powder (MGPP) and passion fruit peel powder (PSPP) in the present study did not enhance Nile tilapia growth and feed utilization after 8 weeks of feeding. while innate immune responses and expression of immune-related genes in tilapia were fed supplement dietary fruits, appeared tend to increase. In addition, only dietary inclusion passion fruit peel powder promoted the expression of antioxidant genes.