PRODUCTION OF GYNOGENETIC AND POLYPLOID CATFISH BY PRESSURE-INDUCED CHROMOSOME SET MANIPULATION

Channel catfish (Ictalurus punctatus) eggs fertilized with sperm from blue catfish (I.furcatus) or channel catfish (60 or 90 s UV-irradiated, 0.08 or 0.12 J/cm(2), respectively; 20-30% motility) were subjected to early hydrostatic pressure (5 min post-fertilization; 8000 psi; 3 min duration) to produce meiotic gynogens or late hydrostatic pressure (90 min post-fertilization) to produce mitotic gynogens. Polyploid hybrid catfish (I.punctatus X I.furcatus) were produced using eggs fertilized with untreated sperm followed by pressure treatments. Eggs fertilized with irradiated sperm (putative haploids) exhibited slow and abnormal development, and did not survive to hatch. Pressure treatments reduced the frequency of normal development at blastula, neurula and tailbud stages compared with stripped controls, Relative survival at 1.5 months was 2% for meiotic and 0.2% for mitotic gynogens, and 66% for triploid and 8% for tetraploid groups, compared with 27% survival of stripped controls. Sex ratios varied among families in hybrid groups but averaged close to 1:1 male:female, whereas offspring in gynogenetic families were all female, Particle size analysis of erythrocyte nuclear volumes indicated 91-100% triploidy induction, but only 4% tetraploidy induction, Although the numbers of gynogenetic channel catfish produced were small, the more than 500 viable offspring surviving represent foundation broodstock to facilitate genetic improvement strategies in this commercially important species.