Family and genetic group effects for resistance to proliferative gill disease in channel catfish, blue catfish and channel catfish×blue catfish backcross hybrids

The severity of gill damage (percentage of gill lamellae with lytic lesions) was determined in juveniles from 10 USDA 103 line channel catfish Ictalurus punctatus full‐sib families, 10 channel catfish×blue catfish I. furcatus backcross hybrid (7/8 channel catfish, 1/8 blue catfish) full‐sib families and a mixed‐family group of blue catfish placed in a commercial catfish pond experiencing proliferative gill disease (PGD)‐related fish mortalities. An initial challenge was conducted with all families, and a second challenge was conducted using the two most susceptible (most gill damage) channel catfish and backcross hybrid families and the two most resistant (least gill damage) channel catfish and backcross hybrid families. In the initial challenge, percentage gill damage was not different between channel catfish (12.3%) and backcross hybrids (11.6%), but was lower in blue catfish (0.2%). Mean percentage gill damage in the second challenge was not different among resistant backcross hybrid families (6.9%), resistant channel catfish families (7.6%) and blue catfish (4.8%), but was higher in susceptible backcross hybrid and channel catfish families (19.0% and 11.9% respectively). The correlation among family means for gill damage from challenge 1 and challenge 2 was r=0.87. Consistent differences between channel catfish and blue catfish and between resistant and susceptible families within genetic groups for gill damage after PGD challenge suggest that there is a genetic component for resistance to PGD and that improving PGD resistance through selection may be possible.