Sustainable Aquafeed with Marine Periphyton to Reduce Production Costs of Grey Mullet, Mugil cephalus

Fish culture sustainability is improved by reducing the fish product content in aquafeeds. Marine periphyton can be used dually for biofiltering mariculture effluent and fish nutrition. The feasibility of periphyton substituting for fishmeal in aquafeed requires evidence. Toward this goal, four iso-protein (42%) and iso-lipid (10%) aquafeeds for grey mullet (Mugil cephalus) were formulated. A control periphyton-free diet consisted of 32% fishmeal, while in the other three diets, periphyton replaced 25%, 50%, or 100% of the fishmeal. Fish were cultured over 104 days with the four diets while measuring their weight gain, specific growth rate, feed conversion ratio, protein uptake, and production value. In a subsequent 35-day trial, and the utilization and digestibility of the feed and dietary amino and fatty acids were measured after feeding fish with the four diets consisting of 1% of Cr₂O₃ as an indigestible marker. The content of protein, lipids, carbohydrates, and ash in the feed and fish was measured using acceptable protocols while fatty acids and amino acids were measured via gas chromatography and high-performance liquid chromatography, respectively. Economic analyses of the reduction in feed and fish production costs were performed using data from the IndexMundi database and research results. Reducing the fishmeal content to 16% did not negatively affect their growth, feed conversion, or protein uptake. The digestibility of dietary protein and lipids was high under the low-fishmeal diets. Eliminating fishmeal from aquafeed inhibited growth, presumably due to a metabolic deficit in the biosynthesis of long-chain polyunsaturated fatty acids under high-salinity conditions. Economically, dietary periphyton reduced the mullet’s aquafeed and production costs, saving USD 0.8 per kg of produced fish with the low-fishmeal (16%) diet. This diet also reduced the fish-in:fish-out ratio to 2.8. The dual use of periphyton improves fish culture sustainability by recirculating nutrients, saving costs, and reducing the fish-in:fish-out ratio.