RESUMEN
Fish, like other oviparous vertebrates, possesses evolutionary advantages of sexual reproduction, which occurs after the attainment of sexual maturity. To understand the time required for attaining sexual maturity by the African catfish, Clarias gariepinus in captivity, juvenile catfish (body wt ~3 g) of one-two months old were collected during late preparatory period (April) and maintained in laboratory tank for 15 months (April 2012-July 2013) under normal temperature, photoperiod, rainfall and food availability. Results indicate that there was a significant (P <0.05) increase in body weight and gonad weight (GSI) in both male and female catfish sampled at 12th and 15th month compared to those sampled at earlier time periods (3rd, 6th and 9th month). Plasma growth hormone (GH) level was also significantly (P <0.05) higher in both male and female catfish at 12th and 15th month than those of preceding months. Histological observation revealed that ovary contained mostly yolky oocytes and testis contained spermatozoa in females and males respectively sampled at 12th and 5th month. Plasma estradiol-17β (E2) and testosterone (T) levels were higher in female and male catfish, respectively sampled at 12th and15th month compared to those of others. Similarly, level of plasma vitellogenin (Vg) in female catfish was also significantly higher. The above findings, thus, suggest that the catfish, C. gariepinus attains sexual maturity after one year of its age to facilitate competency of breeding in successive years
RESUMEN
Effects of daily administration of melatonin for 15 days were evaluated with respect to ovarian activities and plasma gonadotropin (GtH II) and vitellogenin (Vg) levels in intact (INT) and pinealectomized (Px) female catfish, C. batrachus, during preparatory (April), prespawning (May and June), spawning (July) and post-spawning (September) periods. Px (saline control groups) caused a stimulatory effect during preparatory (with respect to Vg synthesis and incorporation) and prespawning (with respect to Vg synthesis) periods whereas no effect was observed during spawning and post-spawning periods with respect to the reproductive parameters studied. During April, melatonin-treatment significantly decreased plasma GtH II levels and percentage of vitellogenic oocytes without any significant changes in plasma Vg levels and gonadosomatic index (GSI). During early prespawning period, in May, 50microg melatonin brought about a significant reduction in plasma GtH II levels in INT group, whereas 100microg caused a decrease in all parameters; on the other hand, in Px groups both dose levels proved to be inhibitory. In June (late prespawning period) melatonin-treatment could not bring about any change in GSI and plasma Vg levels compared to the control groups regardless of Px but plasma GtH II and mean number of yolky oocytes were significantly reduced in melatonin-treated INT group. During spawning period (July) melatonin inhibited the GSI, mean number of yolky oocytes and plasma GtH II levels without affecting plasma Vg levels. In September (post-spawning period), melatonin did inhibit both GSI and plasma GtH II levels. The results, thus, indicate that melatonin showed variable effects (inhibitory and/or no effect) to GSI, mean number of yolky oocytes and plasma Vg levels but a consistent inhibiton of plasma GtH II levels indicating that melatonin may control the reproduction by blocking the GtH II release from the pituitary via affecting the hypothalamo-hypophysial axis.