A DAY-NIGHT RHYTHM OF IMMUNE ACTIVITY DURING SCALE ALLOGRAFT-REJECTION IN THE GULF KILLIFISH, FUNDULUS-GRANDIS

The circadian variation of scale allograft rejection was studied in te leost fish maintained on 12-h daily photoperiods (LD 12:12). Immune ac tivity, measured by melanophore breakdown, was two to three times grea ter during the dark than during the light whether scale allografts wer e transplanted at light onset or light offset. Because rejection occur red predominantly at night, survival times of both primary and seconda ry allografts were about 0.4 days longer when the transplants were mad e at light onset. Immune activity undergoes a robust daily variation i n a teleost fish.