SOME EXPERIMENTS ON THE RELATION OF THE EXTERNAL ENVIRONMENT TO THE SPERMATOGENETIC CYCLE OF FUNDULUS HETEROCLITUS (L.)

Abstract

Within the last decade a considerable body of experimental work has shown that the sexual cycles of many vertebrates of the north temperate zone are regulated in part by the annual cycle of changes in day-length. Little, however, is known about the relation of the ex ternal environment to the sexual cycle of cold water fish. Success in modifying the piscine sexual cycle by light agencies has been reported for the trout (Hoover, 1937; Hoover and Hubbard, 1937), for the minnow, Phoxinus (Spaul cited from Rowan, 1938), and for the stickle back (Tinbergen cited from Rowan, 1938). Craig-Bennett (1930) came to the conclusion that the sexual cycle of the stickleback was regulated primarily by temperature. Hoover (private communication to T. H. Bissonnette) has found that light is ineffective on yellow perch which were kept in water below 44°F. The normal sexual cycle of Fundulus has been described by Mat thews (1938). As in many cold-blooded vertebrates the sexual cycle is a continuous process throughout, with no genuinely inactive phase, although during the winter there is little or no spermatogenetic activity. In the late summer and fall a limited production of spermatogonia takes place. Vigorous spermiogenesis begins in the spring, with a mating period during May and June. Thereafter occurs a gradual deceleration of spermiogenesis with a concomitant testicular involution. It is noticed that the major portion of the spermatogenetic activity is present during the spring when the days are increasing in length, and when the temperature of the water is rising. The experiments here reported are to test the relation of light and temperature to the spermatogenetic cycle of Fundulus.