Precocious induction of oocyte maturation and ovulation in rainbow trout (Salmo gairdneri) : problems when using 17 α-hydroxy-20 β-dihydroprogesterone

Abstract

The efficiency of 17 a-hydroxy-20 (3-dihydroprogesterone (17 a-20 p P) administered alone or after pituitary priming, was investigated in vivo before peripheral migration of the germinal vesicle 4 to 8 weeks prior to natural ovulation. Treatmert with 17 K -20 (3 P alone (2 injections of 3 mg/kg at a 2-day interval) induced oocyte maturation in 94 p. 100 of the fish, but only 25 p. 100 ovulated. Treatment with 17 a-20 p P (3 mg/kg once) 2 days after pituitary priming (1 ml/kg of trout pituitary extract, TPE, containing 3.25 x 10-3 mg/ml of trout gonadotropin, t-GTH) induced maturation in all fish, 59 p. 100 of which ovulated. In both cases, fish in which ovulation did not follow oocyte maturation were killed 15 days after the first injection ; ovarian follicles were either dissected by hand to remove mature oocytes, or incubated in vitro with prostaglandin F 2 œ which induced successful ovulation. In all cases, oocytes obtained from in vivo ovulation, in vitro ovulation by PGF 2 œ ' or manual dissection were fertilized to some extent.