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Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Title: Formalin treatment of Trichondina sp. reduced Flavobacterium columnare infection in tilapia

item Xu, Dehai
item Shoemaker, Craig
item Zhang, Dunhua

Submitted to: Flavobacterium Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 9/10/2015
Publication Date: 10/27/2015
Citation: Xu, D., Shoemaker, C.A., Zhang, D. 2015. Formalin treatment of Trichondina sp. reduced Flavobacterium columnare infection in tilapia [abstract]. Flavobacterium 2015. p. 62.

Interpretive Summary:

Technical Abstract: Bacterium Flavobacterium columnare and protozoan Trichodina spp. are common pathogens of cultured fish. Recent studies on parasite-bacterium interaction show evidence that concurrent infections increase severity of some infectious diseases, especially bacterial diseases. The effect of parasite treatment on F. columnare infection in tilapia is currently unknown. This study evaluated whether treatment of Trichodina sp. parasitized hybrid tilapia (Oreochromis niloticus × O. aureus) with formalin would improve fish survival and reduce F. columnare infection in fish after F. columnare exposure. Hybrid tilapia parasitized by Trichodina sp. were divided into 3 treatment groups. The first group of fish received no parasite treatment. The second group of fish were bath treated with 150 mg L-1 formalin for 1 h. The third group of fish bath treated twice, once daily with 150 mg L-1 formalin for 1 h. The formalin treatment was repeated the following day for a total of 2 days. All fish were then exposed to F. columnare by immersion challenge. The tilapia not treated with formalin showed significantly higher mortality (37.5%) than those treated with formalin (= 16.7%) after exposure to F. columnare. Fish treated twice showed lower mortality (6.37%) than those treated only once (16.7%). The non-treated fish showed significantly higher load of F. columnare in gill, kidney and liver compared to those treated with formalin following exposure to F. columnare. The bacterial load of non-treated fish was 27075 genome equivalents per mg of gill tissue (GEs/mg), 12 fold higher than those treated once with formalin (2250 GEs/mg) or 39 fold higher than those treated twice with formalin (699 GEs/mg) after exposure to F. columnare. This study demonstrated that formalin treatment for Trichodina sp. parasitism reduced bacterial infection as suggested by reduced loads of bacteria in fish tissues and subsequently decreased fish mortality.