Effect of Nannochloropsis oculata and Isochrysis galbana on growth, water quality, biofloc, carcass fatty acids profile, and intestinal bacteria in Nile tilapia (Oreochromis niloticus) raised in zero-water exchange system

In this study, the effects of various algal resources on water quality, growth performance, body fatty acid composition, and intestinal bacteria of Nile tilapia were studied under a zero-water exchange biofloc system. Oreochromis niloticus with an initial mean weight of 2.73±0.27 g, was cultured in five experimental tanks (150 L) including the control group (T1), biofloc group (T2), biofloc+ N. oculata group (T3), biofloc+ I. galbana group (T4), and biofloc+algal (T5) for 60 days. A total number of 225 O. niloticus was used for this study (15 individuals in each replication). The results showed the highest total ammonia nitrogen (4.54±0.05 mg L-1) in the biofloc treatment (p<0.05). There were significant differences in the growth performance among the control group with other treatments (p<0.05). In terms of fillet quality, the highest amount of saturated fatty acids (39.79±0.25%) was found in the biofloc group. The highest monounsaturated fatty acids (41.87±0.99) and polyunsaturated fatty acids (33.25±0.93%) were obtained in the biofloc+algal treatment (p<0.05). All intestinal bacteria in the biofloc group were higher than the control group (P<0.05). The current study demonstrated that biofloc could promote the growth performance of unsaturated fatty acids in the fish fillet.