Influence of tidal cycles on the endocrine control of reproductive activity in common snook (Centropomus undecimalis)

Abstract

The aim of our study was to confirm the role of tidal pattern on the coordination of oocyte maturation and spawning in common snookCentropomus undecimalis. To do so, we studied oocyte maturation during the spawning season in relation to the tidal pattern in both males and females by means ofhistologyand hormonal profiling along thepituitary–gonadal axis. PlasmaLHlevels, as well as transcript levels ofgonadotropingenes (fshβandlhβ) from thepituitariesof sexually mature male and female common snook were analyzed using a heterologousELISAandquantitative RT-PCR, respectively. ThefshβandlhβcDNAs were isolated andphylogenetic analysisof the deduced amino acid sequences revealed strong identity with other teleosts (75–90%). A strong link was found between tide and follicular development irrespective of the time of the day: female snook sampled on the rising tide were all found to have oocytes in the Secondary Growth Stage whereas females sampled at high tide or on the falling tide had oocytes in the later stages of maturation and ovulation. In addition, LH plasma and mRNA levels offshβandlhβincreased during the later stages of vitellogenesis peaking at ovulation in females. Plasmaestradiolandtestosteronesignificantly increased in late vitellogenesis (Secondary Growth Stage) and oocyte maturation (Eccentric GerminalVesicleStep) respectively. Among male common snook sampled, no correlation was identified between tide and gonadal development. In addition,lhβmRNA expression in males peaked at the mid germinalepitheliumstage as for testosterone and11-KTin the blood whilefshβexpression and plasma LH levels peaked at late germinal epithelium stage. This study confirms the role played by tidal cycle on the entrainment of the later stages of oogenesis of common snook and provides a better understanding of the link between environmental andendocrinecontrol of reproduction in this species.