Sex steroid levels, oocyte maturation and spawning performance in Waigieu seaperch (Psammoperca waigiensis) exposed to thyroxin, human chorionic gonadotropin, luteinizing hormone releasing hormone and carp pituitary extract

Abstract

In the present study, we have investigated the sex steroid hormone levels, oocyte maturation and spawning performance in Waigieu seaperch (Psammoperca waigiensis) exposed to different doses (0, (control), 0.05, 0.25 and 0.5 mg/kg fish) of thyroxin (T(4)) both through diet (continuously) and injection (single injection). In addition, we also studied plasma steroid hormone levels and spawning performances in female fish injected with a single dose of D-Ala(6), Pro(9)-Net-mGnRH (LHRHa: 50 microg/kg), human chronic gonadotropin (HCG: 1,500 IU/kg) and carp pituitary extract (CPE: 10 mg/kg). In all experiments, samples were collected at 0, 6, 12, 24 and 48 h after exposure. T4 exposure via dietary route produced differential and enhanced effects, compared with when the compound was injected to the broodstock. A significant association between exposure to dietary T4, elevated plasma steroid hormone levels, maturation-, spawning-, fertilization- and hatching rate, egg diameter, embryogenesis and larval growth were observed. Interestingly, we observed that broodstock groups fed with T4 doses spawned 20 days earlier than the control group. Thus, we propose that these differences may be attributed to higher systemic availability of T4 due to dietary exposure that is easily transferable to eggs and embryos, as opposed to injection that require absorption to increase bioavailability. Furthermore, our results show that LHRHa, CPE and HCG produced significant increase in spawning rate, but significantly reduced fertilization- and hatching rates. Waigieu seaperch is a new candidate for marine aquaculture in Vietnam and relatively little is known about the reproductive biology and endocrinology of this species. Therefore, the present study forms an integral basis for understanding the reproductive endocrinology of a tropical marine finfish with increasing aquaculture prospects and may also contribute in the development of sustainable aquaculture of this species in a developing country such as Vietnam.