The Problem of Self-Fertilization in Teratologically Hermaphroditic Fishes

Abstract

T HE recent case of an hermaphroditic striped bass, Roccus saxatilis, reported by Schultz (1931) is of particular interest, less because of the simultaneous presence of male and female gonadial tissue (which has been reported frequently in the Serranidae), than because of a possibility which he did not state, namely that self-fertilization might have taken place in this specimen. The single ovary and the testis were unilateral and contained well-developed ova and sperm respectively. Unfortunately the ducts are not described, but according to Schultz, Undoubtedly this fish would have spawned both sexual products. The mere occurrence of hermaphroditism in fishes is no longer very novel. Extensive bibliographies on this subject are given by Gemmill (1912) and by Dean (1923). The latter recognizes two groups of hermaphroditic fishes: normal (in which the condition is invariable, or at least occurs in the great majority of individuals), and teratological (in which hermaphroditism is sporadic, or, indeed, very exceptional). Under Teleostei twenty species are listed as of the latter type; certain ones, such as the carp, cod, herring and perch, are reported by several authors. Recent cases of interest were reported in the rainbow trout (Mr'iE, 1923; DeBeer, 1924) and in the silver salmon, Oncorhynchus kisutch (Crawford, 1927). Considering the large number of hermaphroditic individuals which occur sporadically, it seems odd that the possibilty of self-fertilization in the teratological specimens has received so little attention.' Such an event is a matter of considerable interest to the biologist on account of its rarity in animals generally, and because of the problems of sex determination and inheritance which it involves. Recent authors seem to accept without question the statement that certain species of sea perch, Serranus, are constantly hermaphroditic and self-fertilizing; this conclusion appears to rest upon the laboratory observations of Dufoss6 (1856), partly corroborated, so far as the internal anatomy is concerned, by Brock (1878). Brock's findings were also widely accepted by authors, although certain points were called into question by Stephan (1901). Aside from Serranus, most fish hermaphrodites, both normal and otherwise, are described as being protandrous in nature (see especially Stephan, 1901), hence self-fertilization is impossible, since sperm and ova do not ripen simultaneously. The only actual case of teratological self-fertilization that has come to my attention is that reported briefly by Stewart (1894a) in a specimen of Salmo fario. On two occasions ripe ova were caused to be extruded from this trout by artificial abdominal pressure. These eggs were kept isolated, and from them normal and healthy young were reared. They were assumed to have been self-fertilized. Dissection of the fish which