Cooperative Fish and Wildlife Research Units Program: Texas
Education, Research and Technical Assistance for Managing Our Natural Resources

Channel catfish sex is determined at fertilization, according to a male heterogametic system (XX‐XY), but the sex‐determining gene is yet to be elucidated. While progeny sex ratios are typically stable at 1 : 1, sex reversal of genetic male catfish into functional females can be achieved with dietary steroid treatment. Morphological differentiation of ovaries and testes occur at 19 and 90–102 days post‐fertilization, respectively. The considerable time differential between ovarian and testicular differentiations suggests that testis‐inducing signals produced at ≥ 90 dpf are necessary for testicular differentiation in channel catfish –that is, the absence of estrogen production (necessary for ovarian differentiation) earlier in development is insufficient. Thus, testicular differentiation in channel catfish is proposed to occur in two phases: an early phase, when the sex‐determining gene downregulates the gonadal aromatase gene (cyp19a1a) and estrogen production to prevent ovarian differentiation; and a late phase, when masculinizing signals are produced and are required to initiate testicular formation. The products of gsdf and cxcl12 were recently identified for their potential role in the initiation of late‐phase testicular differentiation. All‐male progenies are desirable in channel catfish aquaculture because of their faster growth. A combination of feminizing steroid treatment, selective crossings, and progeny testing has been successfully used to produce YY male individuals that yield all‐male progenies when crossed with normal females. This procedure is time‐ and labor‐consuming, however, and has not been applied in commercial operations. The recent discovery of a male‐specific microsatellite marker may aid in the development of cost‐effective methods to produce YY brood stock.