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Enhanced susceptibility of hybrid tilapia to Flavobacterium columnare after parasitism by Ichthyophthirius multifiliis

De-Hai Xu, Craig A. Shoemaker, Benjamin R. LaFrentz
Aquaculture 2014 v.430 pp. 44-49
Flavobacterium columnare, Ichthyophthirius multifiliis, Oreochromis, farmed fish, genome, hybrids, kidneys, microbial load, mortality, parasitism, pathogens, quantitative polymerase chain reaction
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 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 30,000therontsfish−1 alone; 3) infected by F. columnare ALM-05-53 at 4.59×107CFUmL−1 alone; 4) infected by I. multifiliis at 30,000therontsfish−1 and exposed to F. columnare ALM-05-53 at 4.59×107CFUmL−1; 5) infected by F. columnare TN-3-2012 at 4.27×107CFUmL−1 alone; and 6) infected by I. multifiliis at 30,000therontsfish−1 and exposed to F. columnare TN-3-2012 at 4.27×107CFUmL−1. F. columnare in fish tissues were quantified by quantitative real-time polymerase chain reaction and reported as genome equivalents per mg of tissue (GEsmg−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 30,000therontsfish−1 were ≥5703GEsmg−1 which was between 13 and 17 fold higher than those of non-parasitized fish (≤472GEsmg−1). Similarly, parasitized tilapia showed significantly higher mortality (25%) and bacterial loads (≥1586GEsmg−1) at day 3 post-exposure to F. columnare TN-3-2012 than non-parasitized fish (0% and ≤197GEsmg−1). I. multifiliis parasitism of tilapia enhanced F. columnare invasion and resulted in higher fish mortality.