Submitted to: Journal of Fish Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/2/2003
Publication Date: 7/21/2003
Citation: Bilodeau, A.L., Small, B.C., Wolters, W.R. 2003. Pathogen loads, clearance, and plasma cortisol response in channel catfish following challenge with edwardsiella ictaluri. Journal of Fish Diseases 26:433-437. Interpretive Summary: The role of susceptibility and stress in disease progression for the bacterial disease, enteric septicemia of catfish (ESC) are not well understood. Differences in pathogen loads, pathogen clearance, and cortisol response were measured in two families of channel catfish with different susceptibilities to ESC. The resistant family had consistently lower levels of bacterial DNA in the blood throughout the disease challenge; however, bacterial levels peaked within 24 hours of initial uptake. Cortisol levels peaked within 24 hours of an increase in bacterial levels in resistant fish. Cortisol is an indicator of stress and the relationship between cortisol and bacterial levels indicates that cortisol may interact with the innate immune system and be involved in suppressing acute infection in fish that exhibit resistance to the disease.
Technical Abstract: Differences in the response to disease progression of ESC in channel catfish with different susceptibilities to ESC are not well understood. These differences were investigated in two E. ictaluri-resistant and -susceptible families by examining pathogen loads and pathogen clearance (with real-time PCR), and cortisol response during an ESC challenge. Two families of NWAC103 channel catfish were selected based on mortality rates from three prior experimental E. ictaluri immersion challenges; family 81 (susceptible) mean percent mortality = 86.67 +/- 13.06(SE) and family 110 (resistant) mean percent mortality = 13.33 +/- 11.55(SE). Fish from the susceptible family had higher levels of bacterial cell-equivalents in the blood throughout the trial (p < 0.01), specifically on days 1 through 5, although pathogen clearance occurred at the same rate. Among fish in the resistant family, plasma cortisol levels peaked within 24 hours after the highest levels of bacterial DNA were recorded. Cortisol may interact with the innate immune system and be involved in suppressing acute infection in resistant fish.