Biofloc system avoid the negative effects of diets with suboptimal protein levels on zootechnical performance, intestinal histomorphometry and protein metabolism of Nile tilapia juvenile fed Spirulina biomass (Arthrospira platensis) as alternative protein source

Abstract

Abstract This study aimed to evaluate the effect of the production system (clear water x bioflocs) and the replacement of fish meal with Spirulina biomass (Arthrospira platensis) on productive performance, intestinal histomorphometry, serum biochemistry, and oxidative stress of Nile tilapia juveniles (Oreochromis niloticus) fed suboptimal levels of protein. The design was completely randomized in a 4 x 2 factorial scheme with four replications, four treatments, and two cultivation systems. Four isoproteic (28% crude protein) and isoenergetic (4,000 crude energy kcal kg -1) diets were formulated with 0, 33, 66 and 100% replacement levels of fish meal by Spirulina biomass, supplied for 48 days. Juveniles (0.23 ± 0.01 g) were distributed in 16 circular tanks (70 L) with seven fish per tank. The tanks were divided into two independent recirculation systems (clear water x bioflocs) connected to larger tanks (850 L) equipped with a heating and aeration system. No interaction was observed between the evaluated systems and treatments. Rearing in the BFT system avoided the negative effects of diets with suboptimal protein levels on performance, intestinal histomorphometry and protein metabolism. Lower values lower lipid peroxidation and higher antioxidant capacity were observed in fish reared in the BFT system, showing evidence of improvements in antioxidant responses and lower levels of physiological oxidative stress. Spirulina biomass completely replaced fish meal in the diets of Nile tilapia juveniles without negative effects in intestinal morphometry, protein metabolism and antioxidant response. Replacing 66% of fish meal with Spirulina biomass improved the performance, regardless of the rearing system.