Submitted to: Aquaculture Miscellaneous Publications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2015
Publication Date: 10/2/2015
Publication URL: http://handle.nal.usda.gov/10113/62199
Citation: Xu, D., Shoemaker, C.A., Zhang, D. 2015. Treatment of Trichodina sp. reduced load of Flavobacterium colummnare and improved survival of hybrid tilapia. Aquaculture Report. 2:126-131.
Interpretive Summary: Columnaris caused by bacterium Flavobacterium columnare, is a leading cause of mortality for farm-raised fish in USA and can result in 60-90% mortality among fish in ponds. Parasites and bacteria are commonly found in water of fish farms and studies show that concurrent infections of parasite and bacterium 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 1) evaluated whether treatment of hybrid tilapia parasitized by Trichodina sp. would improve fish survival after F. columnare exposure; and 2) compared the loads of F. columnare in fish tissues between formalin treated fish and non-treated control after immersion exposure to F. columnare. This study demonstrated that treatment of Trichodina sp. parasitized tilapia with formalin reduced parasite infection, resulted in low loads of bacteria in fish tissues and subsequently improved fish survival. This work suggests that prevention and treatment of parasite infection in fish is an important part of fish health management which will not only reduce the direct damage caused by the parasite but will also reduce fish mortality due to secondary bacterial infection.
Technical Abstract: Parasites and bacteria are common inhabitants in water of fish farms. The effect of parasite treatment on Flavobacterium columnare infection in tilapia is currently unknown. This study evaluated whether treatment of Trichodina sp. parasitized hybrid tilapia (Oreochromis niloticus × O. aureus) would improve fish survival and compared loads of F. columnare in fish tissues between non-treated and formalin treated fish after F. columnare exposure. The tilapia parasitized by Trichodina sp. without formalin treatment showed significantly higher mortality (37.5%) than those treated with formalin (less than or equal to 16.7%) after exposure to F. columnare. Among formalin treated fish, fish treated twice showed lower mortality (6.37%) than those treated only once (16.7%). The parasitized fish without treatment showed significantly higher (p<0.05) load of F. columnare in gill, kidney and liver compared to those treated with formalin following immersion exposure to F. columnare. The bacterial load was 27075 genome equivalents per mg of gill tissue (GEs/mg) of parasitized fish without treatment, 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) one day post exposure to F. columnare. The present study demonstrated that formalin treatment to reduce Trichodina sp. parasitism reduced bacterial infection as suggested by low loads of bacteria in fish tissues and subsequently decreased fish mortality.