Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

Albert H. Meier


Reactions against scale allografts in gulf killifish were studied to examine circadian variation and neuroendocrine regulation of immune function. Although melanophores in autografts remain viable indefinitely, melanophores in scale allografts were broken down predominantly at night (12-h scotophases) regardless of the time of transplantation. Daily treatment with hormones or antagonists of neuroendocrine receptors altered the rhythm of melanophore breakdown when administered at light onset or light offset. Daily rhythms of immune activity may be a direct reflection of growth hormone levels and are entrained by exogenous cortisol treatment. Daily nonphotoperiodic environmental stimuli overrode photoperiodic entrainment of immune activity. Peak melanophore breakdown occurred 0-12 h after daily handling disturbances (tank-transfer) or the onset of daily thermoperiods (from 20$\sp\circ$C to 30$\sp\circ$C for either 4 or 12 h durations) and 12-24 h after daily single meal feeding, irrespective of the phase relationship of these stimuli with daily photoperiods. Pretreatment with these stimuli entrained endogenous 24-h immune activity rhythms in fish held under constant environmental conditions, including continuous light. A general anesthetic, MS-222, prevented the entrainment of immune activity rhythms by handling disturbances. The length of time required to reject scale allografts varied in gulf killifish exposed daily to 4-h thermoperiods, disturbances, or single meals at different intervals after light onset. Scale allograft survival times also varied in fish treated daily with hormones or antagonists of neuroendocrine receptors. Daily injections of growth hormone at light onset and daily injections of prolactin at either light onset or light offset decreased scale allograft survival times whereas daily injections of naloxone or propranolol at light offset prolonged scale allograft survival times. The results support the hypothesis that interactions between circadian neuroendocrine oscillations influence immune function in gulf killifish.