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The hybrid between the female channel catfish (Ictalurus punctatus) and the male blue catfish (I. furcatus) is the best genetic type currently available for commercial catfish farming due to their superior traits. However, further genetic improvements can be achieved by selecting parents with increased combining abilities. Twenty female channel catfish and twelve male blue catfish were crossed in a partial factorial mating design, resulting in forty hybrid families. These families were evaluated for early growth in three different rearing systems, including ponds and aquaria. The early growth performance of hybrid catfish was significantly (p < 0.05) affected by the additive gene action of the female parent and the male parent. There were genotype–environment or genotype–age interactions affecting the combining abilities, both the amount and the type of genetic variation. Dam GCA was significant in all environments/ages; however, sire GCA was variable, and SCA was not significant. These findings suggest that reciprocal recurrent selection for growth could potentially improve the performance of F1 hybrid catfish. [ABSTRACT FROM AUTHOR]

Repressible knockdown approaches were investigated for transgenic sterilization in channel catfish, Ictalurus punctatus. Two primordial germ cell (PGC) marker genes, nanos and dead end, were targeted for knockdown, and an off-target gene, vasa, was monitored. Two potentially salt sensitive repressible promoters, zebrafish adenylosuccinate synthase 2 (ADSS) and zebrafish racemase (Rm), were each coupled with four knockdown strategies: ds-sh RNA targeting the 5' end (N1) or 3' end (N2) of channel catfish nanos, full-length cDNA sequence of channel catfish nanos for overexpression (cDNA) and ds-sh RNA targeting channel catfish dead end (DND). Each construct had an untreated group and treated group with sodium chloride as the repressor compound. Spawning rates of full-sibling P1 fish exposed or not exposed to the constructs as treated and untreated embryos were 93% and 59%, respectively, indicating potential sterilization of fish and repression of the constructs. Although the mRNA expression data of PGC marker genes were inconsistent in P1 fish, most F1 individuals were able to downregulate the target genes in untreated groups and repress the knockdown process in treated groups. The results indicate that repressible transgenic sterilization is feasible for reproductive control of fish, but more data from F2 or F3 are needed for evaluation. [ABSTRACT FROM AUTHOR]

The confinement of transgenic fish is essential to prevent their escape and reproduction in natural ecosystems. Reversible transgenic sterilization is a promising approach to control the reproduction of transgenic fish. Therefore, the present study was conducted to develop a reversibly sterile channel catfish ( Ictalurus punctatus ) via the transgenic overexpression of the goldfish ( Carassius auratus ) glutamic acid decarboxylase (GAD) gene driven by the common carp ( Cyprinus carpio ) β-actin promoter to disrupt normal gamma-aminobutyric acid (GABA) regulation. Three generations of GAD-transgenic fish were produced. All studied generations showed repressed reproductive performance; however, this was not always statistically significant. In F 1 , 5.4% of the transgenic fish showed a sexual maturity score ≥ 4 (maximum = 5) at five years of age, which was lower ( p = 0.07) than that of the control group (16.8%). In the spawning experiments conducted on F 1 transgenic fish at six and nine years of age, 45.5% and 20.0% of fish spawned naturally, representing lower values ( p = 0.09 and 0.12, respectively) than the percentages in the sibling control fish of the same age (83.3% and 66.7%, respectively). Four of six pairs of the putative infertile six-year-old fish spawned successfully after luteinizing hormone-releasing hormone analog (LHRHa) therapy. Similar outcomes were noted in the three-year-old F 2 fish, with a lower spawning percentage in transgenic fish (20.0%) than in the control (66.7%). In one-year-old F 2 -generation transgenic fish, the observed mean serum gonadotropin-releasing hormone (GnRH) levels were 9.23 ± 2.49 and 8.14 ± 2.21 ng/mL for the females and males, respectively. In the control fish, the mean levels of GnRH were 11.04 ± 4.06 and 9.03 ± 2.36 ng/mL for the females and males, respectively, which did not differ significantly from the control ( p = 0.15 and 0.27 for females and males, respectively). There was no significant difference in the estradiol levels of the female transgenic and non-transgenic fish in the one- and four-year-old F 2 -generation fish. The four-year-old F 2 -generation male transgenic fish exhibited significantly ( p < 0.05) lower levels of GnRH and testosterone than the control fish. In conclusion, while overexpressing GAD repressed the reproductive abilities of channel catfish, it did not completely sterilize transgenic fish. The sterilization rate might be improved through selection in future generations.