Submitted to: Proceedings of International Congress on Biology of Fishes
Publication Type: Abstract Only
Publication Acceptance Date: April 17, 2006
Publication Date: July 18, 2006
Citation: Bilodeau, A.L., Peterson, B.C. 2006. Immune response of catfish strains exposed to virulent edwardsiella ictaluri. Proceedings of International Congress on Biology of Fishes. July 2006. p. 61. Technical Abstract: Survivorship to ESC (Enteric Septicemia of Catfish) varies among and within strains of commercially raised catfish, however the immunological basis for differences in susceptibiity are not well-understood. We measured mortality, pathogen levels (bacterial DNA), responses of toll-like receptor (TLR3 and TLR5) mRNA expression, and lysozyme activity during experimental challenge with virulent Edwardsiella ictaluri in channel catfish (Ictalurus punctatus) strains: USDA103, Red River (RR), USDA103 x Red River, and Blue catfish (I. furcatus), as well as USDA103 x Blue. Fish were sampled during a 21 day challenge. Mortality levels varied between strains, Blue being the least susceptible (24% mortality) and USDA103 most susceptible (65% mortality). Differences in lysozyme activity paralleled these results with USDA103 having the highest mean lysozyme activity (67.3±28.7 U/mL) and BLUE with the lowest (13.2±3.2 U/mL). Pathogen levels were highest in USDA103 (1.1x10**4 ± 6.4x10**3 ) and lowest in Blue (3.4x10**2 ± 9.3x10**1). There were no notable differences in TLR3 expression, however upregulation was evident during challenge in all strains in all tissues. TLR5 mRNA expression differed by strain in all tissues and over time in spleen and stomach. Similar to differences found in mortality and lysozyme activity, Blue TLR5 mRNA levels differed from the more susceptible channel catfish strains. Both the phenotypic and immune responses measured here suggest that variation in susceptibility to ESC is a function of differences in innate immune response. Understanding these differences will be crucial for enhancing the immune system through selective breeding and in developing disease management protocols.