Development of gonad and brood pouch and expression profiles of cgα, fshβ and lhβ transcripts and plasma 17β-E2 and 11-KT during the first reproductive cycle of farmed big-belly seahorse (Hippocampus abdominalis)

Abstract

Limited data are available regarding the gonadal development of farmed seahorse along with the physiological role of gonadotropins and sex steroids during gonadal maturation. In the present study, we conducted an examination of the developmental stages of gonad and brood pouch during the initial reproductive cycle of the farmed big-belly seahorse (Hippocampus abdominalis), and our results showed that males sexually matured half of a month later than females, and the brood pouch emerged at 3.5-month old and then reached the late-stage at 5.5-month old. Meanwhile, the open reading frame (ORF) of gonadotropin subunits (cgα, fshβ and lhβ) of the big-belly seahorse were cloned and characterized, and tissue distribution profiles of their transcripts were analyzed, revealing their detectability across various tissues, with a notable presence observed in the brain tissues. Furthermore, expression profiles of cgα, fshβ and lhβ transcripts and the plasma levels of 17β-estradiol (E2) and 11-ketotestosterone (KT) in farmed big-belly seahorse during the first reproductive cycle were also investigated. The findings indicated that cgα, fshβ and lhβ transcripts exhibited low expressions at the initial development of ovary or testis, raised continuously and reached their peak levels at the period of spawning or spermation, and they kept gradually increasing accompany with brood pouch growth. It is noteworthy that variation of mRNA levels of fshβ were slightly higher than those of lhβ. Besides, the results showed that plasma 11-KT levels presented an increasing trend during testicular development, peaking in fish with III and IV-stage testis and early-stage brood pouch, and plasma 17β-E2 levels were higher in vitellogenic stage of fish with II-stage ovary and early III-stage ovary. Taken together, these data reveal that gonadotropins and sex steroids likely play a role in the regulation of gonad and brood pouch growth in seahorse. These observations not only contribute to clarifying function of reproductive hormones on growth of gonad and brood pouch of seahorse, but also providing an important theoretical foundation for the artificial breeding of seahorses.