Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2014
Publication Date: 4/5/2014
Publication URL: http://handle.nal.usda.gov/10113/60499
Citation: Xu, D., Shoemaker, C.A., Lafrentz, B.R. 2014. Enhanced susceptibility of hybrid tilapia to Flavobacterium columnare after parasitism by Ichthyophthirius multifiliis. Aquaculture. 430:44-49.
Interpretive Summary: Bacterium Flavobacterium columnare and parasite Ichthyophthirius multifiliis (Ich) are two common pathogens of cultured fish that may result in heavy economic losses for aquaculture. There is no published information available on whether parasite infection will increase the susceptibility of hybrid tilapia to F. columnare. The objective of this study was to evaluate the susceptibility of hybrid tilapia to the bacterium F. columnare, including fish mortality and bacterial loads in fish after parasitism by Ich. The results demonstrated that the Ich-parasitized tilapia showed higher mortality when co-infected with F. columnare than non-parasitized fish. The bacterial loads in Ich-parasitized fish were 10 fold or higher than seen in non-parasitized fish. The results of this study are important to fish health managers and farmers because prevention of parasite infection in fish may not only reduce the direct damage caused by the parasite but may also reduce fish mortality due to bacterial co-infection.
Technical Abstract: Bacterium Flavobacterium columnare and protozoan Ichthyophthirius multifiliis are two common pathogens of cultured fish. The objective of this study was to evaluate the susceptibility of hybrid tilapia (Oreochromis spp.) to the bacterium F. columnare, including fish mortality and bacterial loads in fish gill and kidney after parasitism by I. multifiliis. Fish received the following treatments: 1) non-infected control; 2) infected by I. multifiliis at 30,000 theronts fish-1 alone; 3) infected by F. columnare ALM-05-53 alone; 4) infected by I. multifiliis at 30,000 theronts fish-1 and exposed to F. columnare ALM-05-53; 5) infected by F. columnare TN-3-2012 alone; 6) infected by I. multifiliis at 30,000 theronts fish-1 and exposed to F. columnare TN-3-2012. F. columnare in fish tissues were quantified by quantitative real-time polymerase chain reaction and reported as genome equivalents per mg of tissue (GEs mg-1). The results demonstrated that the I. multifiliis-parasitized tilapia showed significantly (P<0.05) higher mortality (60.4%) when exposed to F. columnare ALM-05-53 than non-parasitized fish (29.1%). The bacterial loads of F. columnare ALM-05-53 in fish infected by 30,000 theronts fish-1 were greater than or equal to 5703 GEs mg-1 which was between 13-17 fold higher than non-parasitized fish (less than or equal to 472 GEs mg-1). Similarly, parasitized tilapia showed significantly higher mortality (25%) and bacterial loads (greater than or equal to 1586 GEs mg-1) at day 3 post exposure to F. columnare TN-3-2012 than non-parasitized fish (0% and less than or equal to 197 GEs mg-1). I. multifiliis parasitism of tilapia enhanced F. columnare invasion and resulted in higher fish mortality.