Effect of dietary protein reduction on growth performance and water quality of the blue streak hap Labidochromis caeruleus (Fryer, 1956) reared in a biofloc system

The 8-week study evaluated the effect of dietary protein reduction on growth performance and water quality of blue streak hap (Labidochromis caeruleus) using biofloc technology (BFT). Fish averaging 0.67 +/- 0.13 g in weight were distributed into 15 polyester tanks, each with a water volume of 60 L within 100 L tanks, accommodating 15 fish per tank. Four isolipidic and isoenergetic diets were formulated with gradually decreasing protein levels (40%, 35%, 30%, and 25%). Four biofloc groups (40P + BF, 35P + BF, 30P + BF, and 25P + BF) and control (C) (40P + without BF) were fed twice daily (09:00 and 17:00) at a rate of 5% of their body weight. Molasses was added to the experimental tanks on a daily basis as an organic carbon source. This ensured that the biofloc tanks had a balanced carbon/nitrogen (C/N) ratio and facilitated control of total ammonia nitrogen (TAN), nitrite-nitrogen (NO2-N), and nitrate-nitrogen (NO3-N) levels. The nutritional composition of the bioflocs obtained from the experimental groups revealed that the crude protein and crude lipid contents were 37.00-38.14% and 1.45-1.52%, respectively (P > 0.05). The best specific growth rate (SGR) (1.68%) and feed conversation ratio (FCR) (2.21) were determined in the 35P group. Based on the overall evaluation of the study's data, it can be concluded that the dietary protein for the blue streak hap (L. caeruleus) can be reduced from 40 to 35% in a biofloc system without any negative effects on health. Improving water quality and providing additional food to fish through zero water exchange and organic carbon addition (BFT) can be considered a sustainable aquaculture technique that can be used in ornamental fish farming.