Lunar and semilunar cycles of spawning activities have been described in many species of fish. It is not known whether these cycles are essentially endogenous in that they might occur in the absence of obvious lunar cues or whether they are directly dependent on lunar-related stimuli such as tidal changes. Our initial studies in gulf killifish, Fundulus grandis, indicate that the spawning cycle persists in fish held under controlled laboratory conditions for many months without any obvious lunar cues (i.e., moonlight or tidal changes). However, it is probable that the fish receive less obvious (subtle) exogenous information that adjusts the phase of the cycle. Meier's investigations will determine whether these persistent cycles are synchronized by an external cue so that peak spawning activity maintains a specific relation to the tidal cycle in the Gulf of Mexico where these fish reside. If the cycles are essentially endogenous but synchronized by subtle external stimuli, he will determine whether the external stimuli provide daily (tidal) or lunar information. Peak of spawning activity occurs at different times of the tidal cycle as a function of site where the fish were obtained. Accordingly, experiments will be carried out to determine whether site specificity is genetically determined or imprinted on the fish during development. The tidal cycle in the Gulf of Mexico where gulf killifish are found has a period near 13.6 days and thus differs from the lunar cycle of moonlight and from tidal cycles in many other areas (about 29.5 days). Furthermore, the semilunar cycles occur in natural as well as controlled laboratory conditions. Experiments will be performed to determine whether such cycles are maintained in other areas, such as in Canada and along the Atlantic coast where related teleost fish exhibit similar cycles.
