Investigation of common diseases on cage reared Nile tilapia (Oreochromis niloticus) in Bakergonj, Barishal, Bangladesh

The present study was conducted to investigate common diseases from cage reared tilapia farms inBakerganj for a duration of 10 months from August 2017 to May 2018. Fingerlings of monosex Nile tilapiawith an average weight of 94.1±5.66 g (mean±SD) were stocked in 10 floating net cages each having anarea of 6.09 m×3.048 m×1.83 m (L×W×H) at the densities of 24 fish/m3. Physical parameters of water(Temperature, DO and pH) were measured at the sampling spot and chemical parameters of water (nitrate,phosphate and ammonia) were analyzed in the laboratory. Both water and diseased fish were collectedmonthly to identify fish diseases. The ranges were: water temperature 20.4oC to 31.3oC, dissolved oxygen5.9 to 6.7 mg/l, pH 7.1 to 8.1, phosphate 0.023 to 0.04 mg/l, ammonia 0 to 0.13 mg/l and nitrate 0 to 10.63mg/l. In the month of September and October, nitrate concentration was high and that might be due todischarging of slaughter wastage substances in water at time of Eid-al-Adha festival. Seven genus ofparasites- Chilodonella sp., Trichodina sp., Gyrodactylus sp., Capillaria sp., Orientocreadium sp.,Eustrongylides sp. and Allocreadium sp. were identified and occurrence of relevant diseases caused by theseparasites were also identified during the study period. Trichodiniasis, Chilodonellosis were main parasiticdiseases. Total count of bacteria was determined and a total of five species of bacteria- V. cholerae, V.parahaemolyticus on TCBS agar, E. aerogenes, S. enteritidis and E. coli on VRB media were identified.Total bacterial load was determined 2.78±0.14x105cfu/ml and 4.26±1.21x106cfu/g in water and tilapiarespectively. Enterococcosiswas the main bacterial disease.