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Title: Effects of Ichthyophthirius multifiliis parasitism on the survival, hematology and bacterial load in channel catfish previously exposed to Edwardsiella ictaluri

Author
item Shoemaker, Craig
item MARTINS, MAURICIO - University Of Santa Catarina
item Xu, Dehai
item Klesius, Phillip

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2012
Publication Date: 6/15/2012
Citation: Shoemaker, C.A., Martins, M.L., Xu, D., Klesius, P.H. 2012. Effects of Ichthyophthirius multifiliis parasitism on the survival, hematology and bacterial load in channel catfish previously exposed to Edwardsiella ictaluri. Parasitology Research. 111(5):2223-2228.

Interpretive Summary: Two important diseases of channel catfish aquaculture in the United States and abroad are enteric septicemia of catfish (ESC) and Ich. ESC is caused by a Gram-negative bacterium (Edwardsiella ictaluri) and Ich is caused by a ciliated protozoan parasite Ichthyophthirius multifiliis. These two pathogens commonly coexist in the aquaculture environment and limited information is available on the effect that coinfection has on catfish health. This study examined the effect of parasitism by Ich on survival, blood cell parameters and bacterial load in catfish previously exposed to E. ictaluri. Parasitism of fish previously exposed to E. ictaluri resulted in increased mortality and changes in hematological parameters. Bacterial load remained elevated in the co-infected fish, while bacteria only exposed fish cleared the infection by day 8. The increased mortality and bacterial load in co-infected fish in our study is most likely due to stress of parasitism. Fish farmers and hatchery managers should be aware of coinfections and the potential negative effect that can result in high mortality and potential economic loss.

Technical Abstract: The effect of Ichthyophthirius multifiliis (Ich) parasitism on survival, hematology and bacterial load in channel catfish, Ictalurus punctatus, previously exposed to Edwardsiella ictaluri was studied. Fish were exposed to E. ictaluri one day prior to Ich in the following treatments: 1)- infected by E. ictaluri and Ich at 2500 theronts/fish; 2)- infected by E. ictaluri only; 3)- infected by Ich at 2500 theronts/fish only; and 4) non infected control. Mortality was significantly higher in fish previously exposed to E. ictaluri and then infected by Ich (71.1 %). Mortalities were 26.7 %, 28.9 % and 0% for fish infected by E. ictaluri only, by Ich only and non-infected control, respectively. Quantitative PCR demonstrated the presence of E. ictaluri in the brain, gill, kidney and liver of fish infected with E. ictaluri regardless of Ich parasitism. At day 8, E. ictaluri parasitized fish had significantly more bacteria present in the brain, gill and liver with no bacteria detected in these organs in the E. ictaluri only treatment suggesting the bacteria persisted longer in parasitized fish. Decreased RBC count and hematocrit in fish at days 8 and 19 after co-infection suggests chronic anemia. Lymphocyte numbers significantly decreased in all infected treatments versus the non-infected controls at day 2, 8 and 19. Lymphopenia suggests the lymphocytes were actively involved in the immune response. Bacterial clearance was probably influenced by the stress of parasitism and/or the mucosal response induced by ectoparasitic Ich that resulted in the higher mortality seen in the co-infected treatment.