Oviducal Fertilization in the South American Catfish, Trachycorystes

Abstract

T HE Commissao Technica de Piscicultura recently made an ecological study of several species of fishes, including the catfish, Trachycorystes, which is rather abundant in some of the artificial lakes of northeastern Brazil, and is esteemed as food. The study of Trachycorystes, which has a peculiar method of reproduction, was made by Dr. Luis Canale, but as he is no longer doing biological work, the writer presents his own observations, pending a more comprehensive investigation. In brief, reproduction in Trachycorystes differs from the usual type in that the spermatozoa are introduced into the oviduct before the maturation of the ova, and fertilization takes place at the time of spawning, independently of the male. The act of insemination was not observed, but the essential facts can be gained from a study of morphological details and spawning behavior. Trachycorystes striatulus Steindachner1 reaches a length of 25 cm. and a weight of 300 to 400 g. The females, in general, are somewhat longer than the males. In the fry, the anal fin is similar in the two sexes, but at the end of 3 or 4 months, at a length of about 12 cm., the genital aperture of the male has migrated from the base of the first anal fin ray toward its distal part. At this age, the male gonads measure 40 mm. in length, and there is no macroscopic evidence of a differentiation in the 30 or more lobes of each side. However, the basal part is somewhat tumid. In the adult male, the genital aperture is situated at the apex of the anal fin, and a sound may be passed internally to a median vesicle which is connected with the gonads. The gonads have two parts: 1. The anterior part, where the spermatozoa are formed and retained until used. In this portion there are 24 to 28 lobules in the form of slightly compressed cones, almost twice as large near the vesicle as at the free end. In general there are groups of two or three lobules, joined at the bases and placed in two irregular series over a membrane. The lobules are white, with distinct red spots. It was not possible to verify, by means of a fine sound, the presence of canals leading from the lobules to the duct of the pseudopenis. 2. The posterior part, at either margin of the median vesicle, composed of 9 to 11 tumid cones arranged in a single series. These are uniformly red and contain only gelatinous substance. The median vesicle, to which the posterior part of the testes are attached, has a complicated structure. It is formed of delicate membranes which inclose gelatinous fusiform bodies grouped in bundles. In a transverse section are seen circles of membranes containing gelatinous substance. These are bound together into bundles by membrane. It seems that the posterior portion of the vesicle is more gelatinous and less well defined in the internal structure than the anterior portion. In the posterior and middle parts, the vesicle is