Plasma steroid and corticosteroid levels in female pacu Piaractus mesopotamicus, Teleostei-Characidae

ABSTRACT

We report the plasma levels of estradiol-l7Beta (E2), testosterone (T), 17(alpha-2Obeta-dihydroxy-4-pregnen-3-one (l7-2OP), and cortisol (F) in female pacu during the reproductive cycle (N = 44) and in females induced to ovulate with an analogue of luteinizing hormone releasing hormone (LHRHa; 10 mug/kg) (N = 24). The plasma hormone levels were determined by validated radioimmunoassays. Females sampled during the reproductive cycle were grouped into 4 gonadal stages: resting, early maturation, advanced maturation and regression. The calculated gonadosomatic index varied from 0.5 ñ 0.1 per cent in resting stage to 8.1 ñ 0.6 per cent in advanced maturation stage. The E2 and T values were highest during the early maturation stage (E2 = 2172 ñ 7.1 pg/ml; T = 412 ñ 58 pg/ml) and the F values were highest during the advanced maturation stage (l32 ñ 5 ng/ml). Females induced to ovulate by LHRHa injection were sampled at 0, 6, and 12 h after injection of LHRHa. Two additional groups were sampled at ovulation and 24 h after ovulation. The E2 values were highest at 6 h (2917 + 65 pg/ml). The T and F values were highest at ovulation (T = 3498 + 77 pg/ml; F = 387 ñ 16 ng/ml) and 17-20P was detected only at vulation (2163 ñ 80 pg/ml).