2012 Annual Report 1a.Objectives (from AD-416): Determine effects of parasitism by Ichthyophthirius or Gyrodactylus on fish susceptibility to Edwardsiella ictaluri and Flavobacterium columnare and develop diagnostic assays for detection of fish pathogen in cultured fish and farm water. 1b.Approach (from AD-416): Catfish and tilapia will be used to evaluate the effect of parasitism by Ichthyophthirius multifiliis or Gyrodactylus on fish susceptibility to Edwardsiella ictaluri and Flavobacterium columnare; and determine if parasites can harbor and subsequently vector the bacterial pathogens using histology, fluorescent and molecular techniques. Rapid molecular and immunological detection assay will be developed and tested for their effectiveness in the detection of bacterial and parasite pathogens. 3.Progress Report: One of the goals for this Non Funded Cooperative Agreement is to determine the effects of parasitism on fish susceptibility to pathogenic bacteria. In aquaculture production, mortality resulting from a single pathogen is rare. More likely, two or more disease agents are present and responsible for disease losses. Two studies were conducted by USDA-ARS scientists in Auburn, AL, to. 1)determine whether bacteria decreased fish survival in parasitized channel catfish and. 2)compare the bacterial quantity in different tissues between non-parasitized and parasitized catfish. The results in those trials demonstrated that parasitized fish showed higher mortality (88.3-91.7%) when exposed to bacteria than non-parasitized fish (10%). The bacterial loads in fish infected by parasites were 40-2,000 folds higher than non-parasitized fish. Parasite infection enhanced the susceptibility of channel catfish to bacterial invasion and caused high fish mortality. This work suggests that prevention of parasite infections in fish will not only reduce the direct damage caused by the parasite but also reduces fish mortality due to bacterial co-infection. The studies also highlight the importance of monitoring parasite infections in aquaculture to optimize fish health. Two papers based on these research results were published in peer-review journals.