RETINOMOTOR RHYTHMS IN THE GOLDFISH, CARASSIUS AURATUS

¹ Franklin and Marshall College, Lancaster, Pennsylvania 17604

1. The goldfish retina shows a persistent circadian rhythm. In constant darkness for three days, the cones continued to shift positions in synchrony with the diel cycle. The amplitude of the shift decreased after the first night. A maximally dark-adapted retina was obtained only on the first night.

2. Individual fish showed considerable variation in the time of occurrence of maximal dark-adaptation. This condition might be attained at any time between 2300 hr. and 0200 hr. The mean values for all fish suggested that the curve of progress of dark-adaptation for the population would be symmetrical with the maximal dark-adapted condition occurring at mid-night.

3. The single and double cones showed some characteristic differences in their behaviors. All cones migrated, but the relative excursions of single and double cones changed after the first night. The migratory patterns suggested the existence of two kinds of single cones.

4. The longevity of persistent rhythms in fish retinas is not known, but the assumption that it ceases after 4 days is based upon misinterpretation of a statement by Arey and Mundt (1941) about the black bullhead.

5. After 8 days in darkness the retina at 1300 hr. was in an intermediate state not dark-adapted. If anything it had drifted toward the light-adapted state.

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