INTEGRATED AQUATIC ANIMAL HEALTH STRATEGIES
Location: Aquatic Animal Health Research
Title: Spleen index and mannose-binding lectin levels in four channel catfish Ictalurus punctatus families exhibiting different susceptibilities to Flavobacterium columnare and Edwardsiella ictaluri
Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 23, 2012
Publication Date: July 30, 2012
Citation: Lafrentz, B.R., Shoemaker, C.A., Booth, N.J., Peterson, B.C., Ourth, D.C. 2012. Spleen index and mannose-binding lectin levels in four channel catfish Ictalurus punctatus families exhibiting different susceptibilities to Flavobacterium columnare and Edwardsiella ictaluri. Journal of Aquatic Animal Health. 24:141-147.
Interpretive Summary: One component of research at the USDA-ARS Catfish Genetics Research Unit includes selectively breeding channel catfish for resistance to the Gram-negative bacterium Edwardsiella ictaluri, which causes enteric septicemia of catfish. Some progress has been made but it is not known what effect breeding for resistance to E. ictaluri will have on the susceptibility of catfish to other important pathogens, such as Flavobacterium columnare, the cause of columnaris disease. In this study, we challenged four channel catfish families with both bacterial pathogens and determined if spleen index and mannose-binding lectin (MBL) levels (potential indicators of natural disease resistance) predicted susceptibility. The results demonstrated that there is variation among families in susceptibility to F. columnare and spleen index and MBL levels do not appear to be predictive indicators of resistance to either bacterial pathogen. An interesting observation was the two families that were most susceptible to F. columnare, were the least susceptible to E. ictaluri. Further research on larger numbers of families is needed to determine if there is any genetic correlation between resistance to E. ictaluri and F. columnare and if spleen index and plasma MBL levels have any utility as predictive indicators of disease resistance.
Edwardsiella ictaluri and Flavobacterium columnare are two bacterial pathogens that impact the channel catfish Ictalurus punctatus aquaculture. Some progress has been made at the USDA-ARS Catfish Genetics Research Unit in selectively breeding for resistance to E. ictaluri; however, the susceptibility of these families to F. columnare is not known. The objectives of this study were to obtain baseline information on the susceptibilities of channel catfish families, maintained as part of the selective breeding program, to E. ictaluri and F. columnare and to determine if spleen index and plasma levels of mannose-binding lectin (MBL) are predictive indicators of susceptibility to these pathogens. Four families of channel catfish were used: family A was randomly chosen from spawns of catfish that had not been selectively bred for resistance; families B, C, and D were families obtained following selection for resistance to E. ictaluri. All four families were challenged by immersion with both bacterial pathogens and the spleen index and plasma MBL levels of unchallenged fish were determined. Mean cumulative percent mortality (CPM) of the families following E. ictaluri challenge ranged from 4 to 33%. Families A and B were more susceptible to F. columnare (mean CPM of three independent challenges, 95 and 93%)than families C and D (45 and 48%), demonstrating that there is genetic variation in resistance to F. columnare. Spleen index and MBL levels were not significantly different, suggesting that these metrics are not predictive indicators of susceptibility to F. columnare or E. ictaluri in the four families that were tested. An interesting observation was the two families that exhibited the highest CPM following the F. columnare challenges had the lowest CPM following E. ictaluri challenge. Further research on larger numbers of families is needed to determine if there is any genetic correlation between resistance to E. ictaluri and F. columnare.