Seasonal and lunar cycles in gonadosomatic indices and spawning readiness of Fundulus grandis

The effects of the phases of the lunar cycle on gonadal development and spawning readiness were studied for one wild and two pond cultured populations of Gulf killifish (Fundulus grandis). Gonadal cycles of all three populations followed a cyclic pattern throughout the reproductive season that lasted from late February to early October. Gonads were largest and more fully developed during two peaks in the cycle, March-April and August-September. This pattern was similar in males and females, although gonad weight changes were smaller in males. No significant effect of the lunar cycle was found on gonadal maturity, although percent ripeness in males for the last quarter moon was significantly lower than that of full and new moon. Significant positive correlations were found between gonad weight and bod length for all three stocks at peak spawning period. Number of ripe eggs in the females increased with body length, but there were large variations in egg numbers because of the discontinuous spawning habit of the fish. Wild fish had heavier gonads and carried more ripe eggs than their pond cultured counterparts, especially at peak spawning periods.