catfish hybrids. Differences in the gene expression of toll-like receptors
(TLR) between the above mentioned groups were observed by Peterson
et al. (2005), where a difference in the ontogeny of gene expression
between channel catfish and blue catfish was proposed as the most
plausible explanation of TLR3 upregulation in hybrids. However, comparisons of immunity including both parental catfish and their hybrids
were performed only by Wolters et al. (1996), who identified an
intermediated (even if insignificantly different) postchallenge antibody
response in channel catfish female × blue catfish male hybrids and
highlighted the importance of the introgression of resistance genes for
disease resistance.