Some observations about the gonads of certain fishes in the middle Parana River

Abstract

This paper deals with the gonads of some species belonging to seven families of Characiformes and Siluriformes fishes found in the middle and lower Parana, River. Most of material was studied from fresh adult fishes in quiescent stage of sexual activity. The form, color, position in the general cavity of body and relation with other organs are described. Some histological data are added. The difference between testis and ovary in the two orders (Characiformes and Siluriformes) as well as in every species, is considered.