Changes in Plasma and Ovarian Steroid Hormone Level in Wild Female Blue Tang Fish Paracanthurus hepatus during a Reproductive Cycle

SIMPLE SUMMARY: Live blue tang fish from Khanh Hoa to Binh Thuan seawaters (a central marine region of Vietnam) were collected monthly for the duration of 12 months and the levels of testosterone (T), estradiol-17β (E(2)) and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) in the plasma and the gonad; gonadosomatic index were determined. The gonadosomatic index (GSI%) maintained high values from April to July and increased from the II to IV ovarian stages and dropped in the V stage. Levels of plasma and ovary T and E(2) and DHP were high from March to July. Plasma T and E(2) levels were low in the II stage when most oocytes were previtellogenic, reaching a peak during spawning and decreased in the V stage when fish were going to late spawning and termination. ABSTRACT: This study aimed to document the seasonal cycle of steroid levels in the plasma and ovary, including testosterone (T), estradiol-17β (E(2)) and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) in relation to ovarian development in wild populations of female blue tang fish. The gonadosomatic index (GSI%) maintained high values from April to July and increased from the II to IV ovarian stages and dropped in the V stage. Levels of plasma, ovary T and E(2) and DHP were high from March to July. Plasma T and E(2) levels were low in the II stage when most oocytes were previtellogenic, reaching a peak during spawning, and decreased in the V stages when fish were going to late spawning and termination. DHP was detected in all stages of the ovary with a higher level in spawning fish but decreased after spawning. These results revealed that T, E(2) and DHP could be involved in ovarian development and DHP may play a significant role as a maturational inducing hormone in blue tang fish.