Banana peel valorization for sustainable aquaculture: Improving fish welfare and water quality

Banana peel (BP) is an underutilized agricultural byproduct with potential applications in aquaculture. This study aimed to examine BP as a functional dietary additive and biochar material for reducing cannibalism-related mortality, modulating neuroendocrine responses, and eliminating water pollutants in aquaculture systems. Experimental diets containing 0, 10, 30, and 50 g/kg of BP powder were fed to juvenile hybrid grouper for 8 weeks to evaluate growth, survival, cannibalism, size variation, and neuroendocrine responses. Untargeted metabolomics was performed to explore metabolic pathways associated with stress and behavior. BP was also converted into biochar, and its adsorption efficiency for malachite green (MG) and copper ions (Cu²⁺) in water was examined. Dietary BP powder supplementation increased survival from 41.67% to 66.67%, reduced cumulative cannibalism from 58.33% to 33.33%, and decreased size variation from 13.80% to 3.29%. However, the final weight decreased from 29.15 to 21.90 g, accompanied by lower weight gain and specific growth rate as well as a slightly higher feed conversion ratio. Physiologically, BP supplementation was associated with an increase in brain serotonin levels, rising from 1.67 ng/mL in the control group to 149.03 ng/mL in the BP50 group. Metabolomics suggested changes in amino acid-, lipid-, energy-, and neuroendocrine-related metabolic pathways. Biochar treatment reduced residual MG and Cu²⁺ concentrations from 200 to 76.56 and 91.39 ppm, respectively. Overall, BP can be valorized as a functional feed additive and a biochar precursor for pollutant adsorption in aquaculture.