NONPHOTIC STIMULI ALTER A DAY-NIGHT RHYTHM OF ALLOGRAFT-REJECTION IN GULF KILLIFISH

The influence of environmental stimuli on a daily rhythm of immune act ivity during scale allograft rejection was investigated in gulf killif ish. Fundulus grandis, Although melanophore destruction in the grafts is largely restricted to the scotophases in killifish held on 12 h dai ly photoperiods (LD 12:12), timed daily netting (tank-transfer ''stres s''), thermoperiods (from 20 degrees to 30 degrees C for 4 or 12 h), a nd feeding altered the expression of this rhythm. Melanophore breakdow n peaked 0-12 h after netting or thermoperiod onset and 12-24 h after feeding, whether the fish were exposed to these nonphotic daily stimul i at the onset or offset of 12-h photoperiods. In fish held under cont inuous light and pretreated with these daily stimuli, 24-h immune acti vity rhythms persisted in the altered phases for several days after th e daily treatments were stopped. These findings suggest that a daily r hythm of immune activity may have adaptive significance in fish.