Role of pineal in the regulation of some aspects of circadian rhythmicity in the catfish, Heteropneustes fossilis (Bloch)

The findings reported here indicate that the pineal organ in catfish is involved in the regulation of locomotor activity rhythms and in some aspects of osmoregulation. Under LD 12:12 regimen, catfish is nocturnally active, with the maximum activity just before dawn. However, under conditions of continuous darkness (DD), the locomotor rhythm became free-running. Pinealectomy abolished the activity rhythm under DD and resulted in arrhythmicity. Circadian rhythms in plasma cortisol, osmolality and electrolytes (Na+ and K+) were also observed. Pinealectomy, though, increased the amplitudes of the rhythm; however the differences were not statistically significant. Removal of pineal significantly increased the mesor values of plasma osmolality and electrolytes, but there were no significant differences in the mesor values of plasma cortisol.