Dietary treatment of Nile tilapia (Oreochromis niloticus) with aquatic fern (Azolla caroliniana) improves growth performance, immunological response, and disease resistance against Streptococcus agalactiae cultured in bio-floc system

The present study was performed to examine the effects of aquatic fern (Azolla caroliniana) (AQF) on growth performance, skin mucus and serum immunities, and disease resistance of Nile tilapia reared in a biofloc system. Three hundred Nile tilapia fingerlings (average 10.48 ± 0.56 g fish-1) were distributed into 15 glass tanks (150 liters tank−1) at a concentration of 20 fish tank−1. A completely randomized design was used in triplicates, where the control group was fed 0 g kg−1 AQF (AQF1), while AQF2, AQF3, AQF4, and AQF5 were fed 25, 50, 100, and 200 g kg−1 AQF, respectively. Growth and immunological specimens were collected every 4 weeks, while disease resistance was conducted after 8 weeks post-feeding. The results showed that dietary administration of AQF significantly promoted the growth rate and feed efficiency of Nile tilapia, with the maximum level noticed in fish fed 100 g kg−1 AQF. However, no significant differences were observed between the AQF1 and AQF5 diets. Similarly, incorporation of AQF resulted in significantly higher skin mucus and serum immunities than the control, except for AQF5. The highest values were observed in fish fed the AQF5 diet. The challenge test showed that in contrast to the control (26.67%), the AQF administrated diets led to significantly higher survivability by 60% (AQF2), 66.67% (AQF3), 83.33% (AQF4), and 53.33 for AQF5. The relative percent survival (RPS) was 45.45%, 54.55%, 77.27%, and 36.36% in AQF2, AQF3, AQF4, and AQF5, respectively. The highest RPS against S. agalactiae was noted in the AQF4 diet. In conclusion, dietary supplementation of 100 g kg−1 AQF can be potentially used as a growth promoter and immunostimulant in Nile tilapia aquaculture.