Effect of pinealectomy and photoperiod on oviposition and gonadal development in the fish, <i>Oryzias latipes</i>

Abstract

Abstract Intact females of Oryzias latipes exposed to 14 hours of light per day for 40 days continued to lay eggs for as long as 35 days. Under a similar photoperiod, pinealectomy shortened the period of oviposition to four days and enucleation to seven days. Moreover, the mean gonosomatic indices (GSI: the gonadal weight expressed as a percentage of the body weight) of intact, pineal‐ectomized, and blinded female fish under the same photoperiod were 10.56 ± 0.53, 3.77 ± 0.31, and 6.31 ± 0.48, respectively. Fish receiving eight hours of light per day laid eggs for only two to seven days, whether they were intact or operated. The GSI's were slightly larger in both pinealectomized and enucleated females than in intact ones (P &lt; 0.1). The significant difference in GSI between blinded females subjected to the eight‐hour photoperiod (3.45 ± 0.48) suggests the presence of an extraocular photoreceptive organ mediating the effects of light on the gonad. The shortening of the period of oviposition in pinealectomized fish seems to show the involvement of the pineal in gonadal development and oviposition; probably the pineal functions as the photoreceptor.