The resistance of Channel Catfish Ictalurus punctatus, hybrid catfish (female Channel Catfish × male Blue Catfish I. furcatus [CB hybrids]), and Channel Catfish and hybrid catfish expressing the introduced cecropin B gene to Ichthyophthirius multifiliis infestation was investigated in two experiments. In experiment I, four fingerling groups were challenged, including cecropin‐transgenic Channel Catfish, cecropin‐transgenic CB hybrids, non‐transgenic Channel Catfish, and non‐transgenic CB hybrids. Non‐transgenic Channel Catfish survived for a shorter time than the other three groups. Survival rate was significantly different between non‐transgenic Channel Catfish and the other groups, which had similar survival rates. In experiment II, non‐transgenic CB hybrids had a less severe infestation than non‐transgenic Channel Catfish. Mortality rates were 62.4% and 40.2% for non‐transgenic Channel Catfish and CB hybrids, respectively. The mean survival time for non‐transgenic hybrids was significantly longer (>5 d) than that of non‐transgenic Channel Catfish. The results suggest that genetic enhancement of Ichthyophthirius resistance can be accomplished in Channel Catfish by either cecropin transgenesis or interspecific hybridization. In addition to survival rate, improving survival time is important because the extension of survival time provides greater opportunity to apply treatments to stop the protozoan infestation.

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Transcription activator-like effector nuclease (TALEN) plasmids targeting the channel catfish gonadotropin-releasing hormone (cfGnRH) gene were delivered into fertilized eggs with double electroporation to sterilize channel catfish (Ictalurus punctatus). Targeted cfGnRH fish were sequenced and base deletion, substitution, and insertion were detected. The gene mutagenesis was achieved in 52.9% of P1 fish. P1 mutants (individuals with human-induced sequence changes at the cfGnRH locus) had lower spawning rates (20.0–50.0%) when there was no hormone therapy compared to the control pairs (66.7%) as well as having lower average egg hatch rates (2.0% versus 32.3–74.3%) except for one cfGnRH mutated female that had a 66.0% hatch rate. After low fertility was observed in 2016, application of luteinizing hormone-releasing hormone analog (LHRHa) hormone therapy resulted in good spawning and hatch rates for mutants in 2017, which were not significantly different from the controls (p > 0.05). No exogenous DNA fragments were detected in the genome of mutant P1 fish, indicating no integration of the plasmids. No obvious effects on other economically important traits were observed after the knockout of the reproductive gene in the P1 fish. Growth rates, survival, and appearance between mutant and control individuals were not different. While complete knock-out of reproductive output was not achieved, as these were mosaic P1 brood stock, gene editing of channel catfish for the reproductive confinement of gene-engineered, domestic, and invasive fish to prevent gene flow into the natural environment appears promising.