Reproduction among Channel Catfish, Blue Catfish, and Their F1and F2Hybrids

Abstract

Reproductive traits of the channel catfish Ictalurus punctatus, the blue catfish I. furcatus, their F1 hybrid—channel catfish female × blue catfish male—and their F2 hybrid were examined. The absence of reproductive isolating mechanisms in F1 and F2 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 fitness is high in F1 and F2 generations, the possibility of introgression with the parent species in the natural environment increases, thereby increasing the potential for risk from F1 generation (and higher) hybrids. F2 hybrid females had a lower frequency of ovulation (P < 0.05; 12.2%) than did channel catfish, blue catfish, and F1 hybrid catfish (83.5, 58.4, and 56.5%, respectively) when these females were induced to spawn with carp pituitary extract and were then hand-stripped. F2 hybrids that ovulated produced fewer eggs per kilogram of body weight (P < 0.05) (923 eggs/kg) than did channel catfish, blue catfish, and F1 hybrid catfish (7,893; 5,600; and 5,676 eggs/kg, respectively). The F1 hybrid had smaller testes per kilogram of body weight than did channel catfish (P < 0.05) (1.08 and 2.72 g/kg, respectively), but it did not have smaller testes than blue catfish (1.71 g/kg). Channel catfish eggs had better fertilization (73.6%) than did F3 hybrid eggs (5.1%, P < 0.05). Channel catfish eggs also had the highest observed hatch (41.5%). Channel catfish maternal genetic effects had a strong positive effect on fertilization percentage, whereas channel catfish–additive genetic effects had a strong positive effect on hatching percentage. Individual epistatic recombination loss had a strong negative effect on hatching percentage. F1 hybrids rarely laid eggs when backcrossed to parent species in aquaria. F2 hybrids did not naturally spawn in open ponds, in the pens in ponds, or in aquaria. F2 breakdown was apparent, and backcrossing was naturally difficult. These reproductive problems in hybrids will make development 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.