Vol. LXXII, No. 2 April, 1937 THE BIOLOGICAL BULLETIN PUBLISHED BY THE MARINE BIOLOGICAL LABORATORY REPRODUCTIVE CYCLES AND SUPERFETATION IN PCECILIID FISHES C. L. TURNER (Prom the Department of Zoology, Northwestern University) INTRODUCTION Reproductive cycles in the pceciliid fishes are of unusual interest for three reasons: (1) this family of fresh-water fishes arose in the tropics and for the most part has remained under tropical and sub-tropical con-ditions where the great seasonal variations in light and temperature found in temperate and arctic zones do not exist; (2) all the species in the family are ovoviviparous. The embryos have fairly large yolk sacs and are retained in the ovarian follicles after fertilization until birth, necessitating a respiratory exchange between parent and embryos. The ovary consequently serves the double function of providing the female gametes and of providing a site and the proper conditions for retaining growing embryos; (3) stiperfetation occurs in some of the genera. In some instances two broods of embryos of different ages are present in the ovaries and in the most extreme case there may be at one time as many as six small separate broods. Pceciliid fishes have been reared in aquaria for years and some of the general facts concerning size of broods, intervals between broods, cor-relation between size of brood and female parent, variation of brood size and intervals between broods at the different seasons of the year, are well known. Bits of reliable information concerning reproduction in a number of genera and species are found in most of the popular books on aquarium fishes. One species in particular, Ganibnsia affinis, has been introduced into new areas in the tropics as a mosquito eradicator and its life history and reproduction have been well studied. Such studies have given relatively little attention, however, to the developing ovocytes within the ovary and the relation between these groups of ovocytes and the broods. In order to study reproductive cycles effectively it has been found necessary to know the stages of development of the embryos and of the 145
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