Morphologic evidence for seasonal changes in the pineal organ of the goldfish, Carassius auratus; a quantitative study.

A quantitative morphologic study of photoreceptor cells in pineal organ of the goldfish was conducted over a period of one year in which the photoperiod-temperature regime simulated the natural environment. Statistically significant seasonal differences were found in cell size, nuclei, nucleoli, mitochondria, endoplasmic reticulum, and Golgi bodies. Peak values generally occurred during the fall and winter months, while minimum values coincided with the reproductive spring and summer seasons. Histological examination of the gonads indicated that the fish followed the normal sexual cycle. These data suggest that the pineal organ is functionally related to photoperiod, temperature, and gonadal maturation in this species.