Effects of disinfectants on bacterial load in a commercial fish hatchery in Mymensingh district of Bangladesh

Abstract

The study was conducted to investigate the effects of four chemical disinfec- tants viz., salt (NaCl), lime, formalin and potassium permanganate (KMnO4) on bacterial loads in water, eggs and fries in a commercial fish hatchery at Trishal upazila in Mymensingh district. Sampling was done in every 10 days interval for each month from March to May 2016. Hatching trays (12"×7") were disinfected using 40 ppm salt water and 20 ppm potassium perman- ganate. Cisterns (84 ft² each) were washed and disinfected with combination of lime (5 g ft⁻²) and salt (30 g ft⁻²) followed by application of potassium permanganate (1 ppm) and formalin (0.25 ppm). After disinfecting, bacterial load in hatching tray water reduced immediately than that of overhead tank water. Bacterial load was determined using serial dilution technique and expressed as colony forming unit (cfu mL⁻¹). The average highest bacterial load in overhead tank water was 4.89±1.71×107 cfu mL⁻¹ while the highest load in hatching tray water was 3.30±3.54×106 cfu mL⁻¹. The bacterial load of cistern water (1.43±0.75×103 cfu mL⁻¹) decreased compared to tank water and gradually increased after six days of giving hormone treated feed. To prevent infection of eggs saline water was applied and lower bacterial load of 4.25±2.67×102 cfu mL⁻¹ was observed. The study revealed that use of chemical disinfectants in the initial stages of hatchery operation can decrease the bacterial load and thus reduces the chance of infection and diseases of eggs and fry.