Study on application of bacillus spp. In the aquaponic system of swamp eel(Monopterus albus Zuiew,1793)

Abstract

This study was conducted to evaluate the effects of Bacillus spp. on water quality, bacterial dynamics, and growth performance of swamp eel (Monopterus albus) in the aquaponic system. The study was conducted with two steps of isolation and application of the isolated bacillus spp into the aquaponic system of swamp eel. The verification experiment was performed with two treatments: a control without isolated bacterial supplementation and a treatment supplemented weekly with isolated Bacillus spp. at 10⁶ CFU/mL, each in triplicate. Key water quality parameters (NH₄⁺, NO₂⁻, NO₃⁻, COD, BOD5, DO, pH) were monitored, with emphasis on the final month when bacterial colonization was expected to be more stable. Results indicated that Bacillus spp. contributed to lower NH₄⁺ concentrations and moderated NO₃⁻ accumulation compared to the control, although NO₂⁻ remained consistently low in both treatments. Swamp eels in the Bacillus group achieved significantly higher growth performance (final weight 13,84 ± 0,28 g) than the control group (11,61 ± 0,50 g, p < 0.05). Bacterial densities in the treatment were significantly higher and more stable, confirming successful colonization. Watercress (Nasturtium officinale) production did not grow well at the end of this experiment in both treatments; it may be due to planting experiment and need further observations. Overall, supplementation with Bacillus spp. improved water quality stability and swamp eel performance, demonstrating potential as a sustainable bioaugmentation strategy for aquaponic eel culture in the Mekong Delta.