Valorization of bovine tannery fleshing waste as a fish meal replacer: a conceivable green approach

The study intended to utilize bovine tannery fleshing (BTF) — a significant contributor of solid wastes in leather industries, in its unhydrolyzed form (raw fleshing flour [RFF]) as well as in fermented form (fermented fleshing flour [FFF]) as fish meal (FM) replacer in formulated aqua feeds. In line with this, experimental diets were formulated, characterized, and evaluated for their virtue. Improvement in the physical quality of diets was achieved with FFF incorporation, enabling better pelletability, palatability, and feed texture. As the formulated diets were of sinking type, feeding trials on column as well as bottom feeders were concertedly attempted, as a value-added application of proteinaceous feed ingredient (BTF) in aquaculture sector. FFF inclusion diets proved superior to RFF inclusion diets. Maximum protein and lipid retentions of 89% and 92% were evidenced. Fish feeding experiments disclosed the productive impact of substituting FM with FFF by 50 and 75% on the performance (fish growth) of Cirrhinus mrigala (19.03 cm final length, 112.89 g Kg^-1 final body weight, and 99% survival rate) and Labeo rohita (22.19 cm final length, 214.99 g Kg^-1 final body weight, and 97% survival rate) respectively, with enhanced muscle biochemical compositions. FFF inclusion diets best suited column feeders than bottom feeders, with acceptable feed conversion ratio (< 2) and about 65% and 69% of protein in Rohu and Mrigal, respectively after 90 days of feeding. Absence of feed related mortality and multimycotoxins in FFF inclusion diets authenticated its invulnerable nature, signifying the need of bacterial fermentation processes to pull out the maximum worth of the solid waste. Thus, bovine tannery fleshing (BTF) would probably be used as a relatively inexpensive, effectual, safe, and an absolute source of protein for marine animals, reinforcing aquaculture business to strengthen up its profitability and eventually; this is an assuring conscientious solid waste management strategy that could be scaled-up to develop high-quality aquaculture feeds.