Sexual maturity,seasonal estrus,and gestation in female Indo-Pacific bottlenose dolphins Tursiops aduncus inferred from serum reproductive hormones

Reproductive hormones in serum concentrations of progesterone,estradiol,and testosterone in female Indo-Pacific bottlenose dolphins(Tursiops aduncus,n=12)housed in Ocean Park Hong Kong were investigated in the present study.Results showed that,onset of puberty of captive Indo-Pacific bottlenose dolphins was at 5 years while sexual maturity was at 6.Average serum progesterone concentrations in non-pregnant sexually mature individuals was 0.33(0.25–0.97)ng/mL(interquartile),significantly higher than in immature ones 0.26(0.25–0.38)ng/mL.This study found significant difference in serum estradiol concentrations between individuals at the onset of puberty(9.5±1.7 ng/mL,±SD)and not(below detection limit 9 pg/mL).A slightly seasonal breeding pattern,with progesterone values tend to be higher from February to October(0.38[0.25–1.07]ng/mL)was inferred.During pregnancy,serum progesterone concentrations range from 10.54±8.74 ng/mL(indexed month post-conception[IMPC]0)to 25.49±12.06 ng/mL(IMPC 2),and display a bimodal pattern with 2 peaks in early-(25.49±12.06 ng/mL,IMPC 2)and late-pregnancy(21.71±10.25 ng/mL,IMPC 12),respectively.Serum estradiol concentrations can seldom be detected in early-pregnancy and increase constantly in mid-(9.45±1.83 pg/mL)and late-pregnancy(11.88±3.81 pg/mL),with a spike(15.45±6.78 pg/mL)1 month prior to delivery.Serum testosterone concentrations elevate significantly in IMPC 7(0.36±0.10 ng/mL)compared to other months(0.16±0.10 ng/mL)of the year.The present study provides normal concentration profiles for some reproductive hormones in female Indo-Pacific bottlenose dolphins and can contribute to the breeding monitoring of this species.Also,our study would shed further light on the reproductive physiology of small cetaceans.