ARS | Publication request: Parasitism by protozoan Ichthyophthirius multifiliis enhanced invasion of Aeromonas hydrophila in tissues of channel catfish

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 12, 2011
Publication Date: December 1, 2011
Repository URL: http://hdl.handle.net/10113/55584
Citation: Xu, D., Wei Pridgeon, Y., Klesius, P.H., Shoemaker, C.A. 2011. Parasitism by protozoan Ichthyophthirius multifiliis enhanced invasion of Aeromonas hydrophila in tissues of channel catfish. Veterinary Parasitology. 184:101-107.

Interpretive Summary: In aquaculture production mortality resulting from a single pathogen is rare. More likely, two or multiple disease agents are present and responsible for disease losses. The bacteria Aeromonas hydrophila and the parasite Ichthyophthirius multifiliis (Ich) are two common pathogens of cultured fish. They can result in mass kills of cultured fish and lead to high economic losses to aquaculture. Currently there is no information available for the effect of coinfection by Ich and A. hydrophila on bacterial load and survival in channel catfish. This study determined 1) whether A. hydrophila decreased fish survival in Ich-parasitized channel catfish and 2) compared the bacterial quantity in different tissues between non-parasitized and Ich-parasitized catfish. The results demonstrated that the Ich-parasitized catfish showed lower survival (30%) when exposed to A. hydrophila by immersion than non-parasitized fish (95%). High survival was observed in catfish exposed to Ich alone (90%) or A. hydrophila alone (95%). Fish tissues from Ich-parasitized fish showed higher load (5-24 fold) of A. hydrophila than non-parasitized fish tissues after exposure to A. hydrophila. This study provides evidence that parasitism enhanced bacterial invasion and resulted in high fish mortality. The study results are important to the aquaculture industry and will help fish farmers and health managers better define the impact of parasites on bacterial diseases in fish.

Technical Abstract: Ichthyophthirius multifiliis Fouquet (Ich) and Aeromonas hydrophila are two common pathogens of cultured fish. Currently there is no information available for the effect of coinfection by Ich and A. hydrophila on bacterial load and survival in channel catfish. Two trials were conducted in this study to 1) determine whether A. hydrophila decrease fish survival in Ich-parasitized channel catfish and 2) compare the bacterial quantity in different tissues between non-parasitized and Ich-parasitized catfish by real-time polymerase chain reaction (qPCR). The results demonstrated that the Ich-parasitized catfish showed significantly (P<0.05) lower survival (30%) when exposed to A. hydrophila by immersion than non-parasitized fish (95%) in trial I. High survival was observed in catfish exposed to Ich alone (90%) or A. hydrophila alone (95%). Similar results were observed in trial II: catfish infected by both Ich and A. hydrophila showed the lowest survival (10%) than fish infected by Ich (40%) alone or by A. hydrophila alone (60%). Using qPCR specific primers targeting the aerolysin gene of A. hydrophila, bacteria loads in tissues were quantified between Ich-parasitized fish and fish free from parasite. Skin, gill, kidney, liver and spleen in Ich-parasitized fish showed significantly higher load (5-24 folds) of A. hydrophila than non-parasitized fish after exposure to A. hydrophila. This study provides evidence that parasite infections enhance bacteria invasion and cause high fish mortality.