Seasonal effects of pinealectomy on the ovary of the catfish Heteropneustes fossilis (Bloch) under normal photothermal conditions.

Pinealectomy of Heteropneustes fossilis held under normal photoperiod and ambient temperature produced season-dependent effects on ovarian activity. When the fish were pinealectomized in the preparatory phase (early light-responsive period) and maintained until the early prespawning phase, there was an accelerated growth of the ovary, as adjudged from increased gonado-somatic index (GSI), ovarian histology, elevated ovarian total protein and ascorbic acid levels, and an increased level of serum alkali-labile protein phosphorus (vitellogenin). Pinealectomy was ineffective in the prespawning and spawning (late light-responsive phase) and postspawning (light refractory) phases. The results suggest that the pineal exerts an inhibitory effect on the hypothalamo-hypophysial-ovarian axis and synchronizes temporally ovarian activity in response to increasing photothermal conditions such that spawning takes place at a time most suitable for the survival of the young.