Abstract
Negative, slow and graded potential was recorded from the pineal organ of two fishes, ayu, Plecoglossus altivelis, and rainbow trout, Salmo gairdneri irideus. Some characteristics of the potential were examined and the following results were obtained.
1. The response to test light (20 lux) occurred, in succession to the momentary potential drop. This potential drop (7-26mV in ayu and 10-30mV in rainbow trout) was thought to be the membrane potential of the cell.
2. In both fishes, response amplitude increased linearly with log intensity of light and reached the maximum amplitude at about 30 lux.
3. In rainbow trout, the latency was maximum (380 msec) at 0.01 lux and minimum (50 msec) at 300 lux, (mean values of 4 fishes). It decreased linearly with log intensity of light.
This slow potential seems to originate from a pineal photoreceptor cell, but further investigations are necessary for a definite conclusion.
