| Summary: | The research was conducted from May to December 2022 in Lao Cai province. A
total of 192 fish samples were collected from the traditional cultured fish group and coldwater cultured fish group. Freshoscopy method has been applied for fungal indicators, isolated culture for bacteria and PCR technique for virus indicators. The results showed that fungal agents were detected with a high infection rate in both groups of traditionally cultured fish (83.3%) and cold-water cultured fish (66.7%); Among them, more than 90% are fungus carrying Branchiomyces sp.; The remaining is Dermocystidium sp. and Aphanomyces sp, the recorded period is from May to December. Meanwhile, bacterial causes were found to be lower, infection rate of bacterial species Edwardsiella sp.; Streptococcus sp. and Aeromonas sp. recorded between 20 and 35%, especially in September and October, the infection rate is lower than other months. To limit the damage, water needs to be treated before flowing into the pond/farming tank, periodically supplement vitamin C or multivitamins to increase the fish's resistance, well control environmental factors, especially temperature, amount of ammonia and amount of organic matter in the pond.
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