Hybrid catfish (♀ channel catfish, Ictalurus punctatus × ♂ blue catfish, I. furcatus) account for ~70% of the catfish production due to superior performance compared to the parent species for several traits. Xenogenesis has been utilized to potentially produce hybrid catfish embryos more efficiently by transplanting unsorted gonadal cells from donor diploid blue catfish into triploid channel catfish fry. Then xenogenic channel catfish males are mated with normal female channel catfish to produce 100% hybrid progeny. The stem cells have not undergone meiosis and are isogenic. This offers an opportunity to conduct reciprocal recurrent selection and identify the absolute best individual female channel catfish and male blue catfish that have the best combining ability, resulting in the ultimate hybrid progeny. The gonads of these individuals can essentially be ’cloned’ and multiplied into large populations through xenogenesis, ensuring perpetuity without inbreeding and maintaining consistent performance of hybrid progeny. An impediment to this approach is that the brooders with the best combining ability are not identified until they reach maturity, at which point the number of gonadal stem cells is low, allowing for the production of only a few xenogenic progeny. However, if the spleen and kidney cells have colonizing and proliferation abilities, potentially 400 and 800 fry, respectively, could be injected from these donor organs alone.
Triploid channel catfish surrogates were injected at 5 days post hatch (DPH) with either unsorted gonadal, kidney, spleen, or somatic cells (extracted from skin tissue) labeled with PKH26 fluorescence dye. PKH26 and PCR analysis indicated that 100.0, 90.9, 54.5 and 0.0 percent of fry injected with mixed gonadal, kidney, spleen and somatic (skin) cells were xenogenic. Theoretically, this would allow production of 1, 727, 218, and 0 xenogenic fry from gonad, kidney, spleen, and somatic cells, respectively from adult catfish. Colonization and proliferation of donor cells (predictors of future fertility) were evaluated using PKH26 by calculating percent cell (<150 μm2) and cluster areas (>150 μm2). At 45 DPH, gonadal xenogens had a larger cell area than the somatic (P = 0.004) and spleen xenogens (P = 0.031). By 90 DPH, gonadal (P = 0.003) and kidney surrogates (P = 0.029) had higher cell areas than spleen surrogates (P = 0.134). By 90 DPH, no fluorescent dye was found in somatic surrogates. Cell area for surrogates injected with gonadal (P < 0.001), kidney (P < 0.014), and spleen cells (P < 0.012) increased in size from 45 to 90 DPH. Cluster area also increased in size for surrogates injected with both gonadal (P < 0.001) and kidney cells (P < 0.002). Total cluster and cell area was highest for gonadal xenogens followed by kidney and then spleen xenogens. Kidney cells appear to be a viable option, and potentially spleen cells as well, for generating clonal populations of catfish to permanently fix maximum combining ability. Additional improvements could be achieved through cell purification.