Production of viable homozygous, doubled haploid channel catfish (Ictalurus punctatus).

Production of doubled haploids via mitotic gynogenesis is a useful tool for the creation of completely inbred fish. In order to produce viable doubled haploid channel catfish, we utilized hydrostatic pressure or thermal treatments on eggs fertilized with sperm that had been exposed to ultraviolet light. At 1.5 h post-fertilization, the embryos were exposed to either 590 kg/cm(2) hydrostatic pressure for 3 min, 37 degrees C for 5 min, or 41 degrees C for 3 min. In the pressure-treated group, only 21 offspring hatched from five spawns with family sizes of one, two, two, four, and 12 offspring each. Eight embryos from the 37 degrees C treatment and 32 embryos from the 41 degrees C treatment survived to hatch. Genotype analysis using microsatellite loci demonstrated all 21 offspring resulting from pressure treatment were homozygous at the 64 loci tested, and none contained alleles unique to the donor male. Eleven of 32 offspring from the 41 degrees C treatment were homozygous at the 18 loci tested, while 21 offspring were heterozygous at six to 12 of these loci. Again, no offspring contained alleles unique to the donor male. However, all eight offspring from the 37 degrees C treatment were heterozygous at multiple loci, and one contained unambiguous paternal alleles. These experiments demonstrated our ability to produce viable homozygous, doubled haploid channel catfish. Doubled haploid catfish can be used to create completely inbred populations for genetic analyses, and homozygous genomic templates will be useful in gene identification and genome characterization.