article · Aquaculture Reports
Supplementing the diet of Nile tilapia reared in biofloc systems with the aquatic fern Azolla caroliniana improves growth, feed efficiency, and immune defences. Across an eight-week trial evaluating inclusion levels between 0 and 200 grams per kilogram of feed, tilapia receiving 100 grams per kilogram achieved the best overall growth and feed utilisation. Diets supplemented with the aquatic fern also enhanced skin mucus and serum immune indicators compared to control diets. When challenged with the bacterial pathogen Streptococcus agalactiae, fish fed the aquatic fern exhibited substantially improved survival rates, peaking at over 83 percent survival in the group fed 100 grams per kilogram, compared with under 27 percent in the control group. Overall, an inclusion rate of 100 grams per kilogram shows clear potential as a functional feed additive to bolster productivity and disease resistance.
Bacterial diseases such as Streptococcus agalactiae cause heavy losses in commercial aquaculture. Using plant-based supplements like aquatic ferns provides fish farmers with a practical, natural method to boost fish immunity, reduce disease mortality, and improve feed efficiency without relying on synthetic chemicals or antibiotics.
This research provides applied and tested evidence for fish feed manufacturers and tilapia producers operating biofloc aquaculture systems. The aquatic fern could be formulated into commercial feed additives to stimulate growth and protect stock from streptococcal infections. Further commercialisation will require scaling feed production, verifying shelf life, and confirming efficacy under commercial farm conditions beyond controlled tank trials.
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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.
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DOI: 10.1016/j.aqrep.2022.101114
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