Dual Role Of Streptomyces Strains: Reduction of Aeromonas Counts In Both Culture Water And The Intestine, And Growth Enhancement of Discus Fish (Symphysodon sp.)

Abstract

Discus fish (Symphysodon sp.) brings the largest export turnover to the ornamental fish industry in Vietnam. The intensive farming of discus fish to meet export market demand leads to a higher risk of bacterial disease, with Aeromonas being the main infectious agent. Continuous antibiotic use exerts selective pressure, fostering the emergence of antibiotic-resistant bacterial strains capable of causing diseases in fish. Streptomyces sp. considered as probiotics with the role of replacing antibiotics in applications such as promoting growth, improving survival rates, and controlling pathogenic bacteria in aquaculture. The primary objective of this study was to assess the influence of Streptomyces sp. on the growth performance, and Aeromonas density in intestine of discus fish and in culture water. Discus fish fed diets containing Streptomyces sp. TM1, TM7, and TM22 showed significantly higher growth parameters (45.24 - 58.72% of final body weight - FBW, 14.8 - 16.66% of final body length -FBL, 16.03 – 20.87 % of specific growth rate of weight – SGRW, 10.79 - 12.05 % of specific growth rate of length – SGRL, and 41.48 – 46.54 % of feed conversion ratio – FCR) compared to the control. Additionally, total Aeromonas densities of the fish treated with TM1, TM7, and TM22 showed a notable decrease compared to the control treatment in the rearing water with log CFU/ml values of 4.517 (Control), 2.554 (TM1), 2.571 (TM7), 2.222 (TM22) and in the intestines of fish with log CFU/g values of 5.597 (Control), 3.828 (TM1), 3.806 (TM7), 3.648 (TM22). Streptomyces sp. TM1, TM7, and TM22 could decreased total Aeromonas count in the gut of discus fish and in the rearing water, and boost the growth performance of discus fish (Symphysodon sp.).