Effects of yellow passion fruit (Passiflora edulis) residue in diets for Oreochromis niloticus in a recirculating aquaculture system with integrated lettuce cultivation

The inclusion of agro-industrial residues in fish diets represents a sustainable strategy for modern aquaculture. This study investigated the effects of incorporating yellow passion fruit (Passiflora edulis) residue into diets for Nile tilapia (Oreochromis niloticus) fingerlings reared in a recirculating aquaculture system (RAS) integrated with lettuce (Lactuca sativa) cultivation. Over a 60-day period, 12 tanks were used in a completely randomized design with four treatments: T1 (12% yellow passion fruit residue (PFR) with lettuce), T2 (12% PFR without lettuce), T3 (0% PFR with lettuce), and T4 (0% PFR without lettuce), each with three replicates and a stocking density of 25 fish per tank (3.75 ± 0.40 g; 5.84 ± 0.50 cm). The presence of lettuce significantly reduced ammonia levels, improving water quality. No significant differences in growth performance were observed among treatments. Antioxidant capacity was enhanced by the inclusion of 12% PFR, showing higher activities of catalase, superoxide dismutase and glutathione S-transferase. Despite a reduction in intestinal villi height in fish fed 12% PFR, no negative impacts on growth performance were identified. The study demonstrates that integrating lettuce into the RAS is effective for water treatment and that using up to 12% PFR in diets is a sustainable, functional, and promising approach for Nile tilapia, contributing to more efficient and environmentally responsible production systems.