Reproduction among channel catfish, blue catfish, and their F-1 and F-2 hybrids

Reproductive traits of the channel catfish Ictalurus punctatus, the blue ca tfish I. furcatus, their F-1 hybrid-channel catfish female x blue catfish m ale-and their F-2 hybrid were examined. The absence of reproductive isolati ng mechanisms in F-1 and F-2 generations is important in terms of allowing for breeding programs for the development of a synthetic breed that has the best culture traits from the two species. Conversely, if reproductive fitn ess is high in F-1 and F-2 generations, the possibility of introgression wi th the parent species in the natural environment increases, thereby increas ing the potential for risk from F-1 generation (and higher) hybrids. F-2 hy brid females had a lower frequency of ovulation (P < 0.05: 12.2%) than did channel catfish, blue catfish, and F-1 hybrid catfish (83.5, 58.4, and 56.5 %, respectively) when these females were induced to spawn with carp pituita ry extract and were then hand-stripped. F-2 hybrids that ovulated produced fewer eggs per kilogram of body weight (P < 0.05) (923 eggs/kg) than did ch annel catfish, blue catfish, and F-1 hybrid catfish (7,893; 5,600; and 5,67 6 eggs/kg, respectively). The F-1 hybrid had smaller testes per kilogram of body weight than did channel catfish (P < 0.05) (1.08 and 2.72 g/kg, respe ctively), but it did not have smaller testes than blue catfish (1.71 g/kg). Channel catfish eggs had better fertilization (73.6%) than did F-3 hybrid eggs (5.1%, P < 0.05). Channel catfish eggs also had the highest observed h atch (41.5%). Channel catfish maternal genetic effects had a strong positiv e effect on fertilization percentage, whereas channel catfish-additive gene tic effects had a strong positive effect on hatching percentage. Individual epistatic recombination loss had a strong negative effect on hatching perc entage. F-1 hybrids rarely laid eggs when backcrossed to parent species in aquaria. F-2 hybrids did not naturally spawn in open ponds, in the pens in ponds, or in aquaria. F-2 breakdown was apparent, and backcrossing was natu rally difficult. These reproductive problems in hybrids will make developme nt of synthetic breeds from channel catfish and blue catfish difficult and will reduce the likelihood of introgression between the two species in the: natural environment.