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 m in duration) to produce meiotic gynogens or late hydrostatic pressure (90 min post-fertilization) to produce mitotic gynogens. Polyploid hyb rid catfish (I.punctatus X I.furcatus) were produced using eggs fertil ized with untreated sperm followed by pressure treatments. Eggs fertil ized with irradiated sperm (putative haploids) exhibited slow and abno rmal development, and did not survive to hatch. Pressure treatments re duced the frequency of normal development at blastula, neurula and tai lbud stages compared with stripped controls, Relative survival at 1.5 months was 2% for meiotic and 0.2% for mitotic gynogens, and 66% for t riploid and 8% for tetraploid groups, compared with 27% survival of st ripped controls. Sex ratios varied among families in hybrid groups but averaged close to 1:1 male:female, whereas offspring in gynogenetic f amilies were all female, Particle size analysis of erythrocyte nuclear volumes indicated 91-100% triploidy induction, but only 4% tetraploid y induction, Although the numbers of gynogenetic channel catfish produ ced were small, the more than 500 viable offspring surviving represent foundation broodstock to facilitate genetic improvement strategies in this commercially important species.