2011 Annual Report 1a.Objectives (from AD-416) Determine the influence of external parasitic infestation on innate resistance in fish to bacterial infection and disease and the effect on the acquired immune responses to bacterial infection and disease on fish vaccination. 1b.Approach (from AD-416) Tilapia, catfish, pintado, pacu and other species of warmwater fish will be used to determine the effect of external parasitic infestation by Gyrodactylidae and Dactylogyridae monogeneans, trichodinids and/or Ichthyophthirius multifiliis on the innate immune responses to Streptococcus (S.) iniae, S. agalactiae and Aeromonas (A.) hydrophila under experimental infection and disease. The effect of these parasites on the protective acquired immune response to S. iniae, S. agalactiae, and A. hydrophila infection and disease will also be determined on fish vaccination against these bacterial pathogens. The techniques employed include those from the areas of parasitology, bacteriology, immunology, histology and molecular biology to quantitatively measure parasite and bacteria infectivity, pathology, ELISA antibody responses and molecular responses of immune and related genes in parasitized fish subjected to bacterial infections. The data will be subjected to statistical analysis. 3.Progress Report The objective is to determine the influence of external parasitic infestation on innate resistance in fish to bacterial infection and diseases on fish vaccination. Significant progress was made to determine the effect of parasitism on the susceptibility of channel catfish to Edwardsiella (E.) ictaluri infection and it has been found that dual infection of protozoan parasite Ichthyophthirius (Ich) and E. ictaluri significantly increased fish mortality compared to fish only infected by E. ictaluri or only infected by parasite Ich. Significant progress was also made to determine the effect of parasitism on the efficacy of Streptococcus iniae formalin-killed vaccine in tilapia. The results demonstrated a reduction in vaccine performance in fish infected by parasites compare to non-parasitism fish. This project involved the sabattical work of a visiting international scientist at the Auburn location and will continue to be monitored with e-mails and phone calls.