Morphology and histology of the male reproductive system in two species ofinternally inseminating South American catfishes, Trachelyopterus lucenai and T-galeatus (Teleostei : Auchenipteridae)

As part of an effort to characterize reproductive modifications in internal ly inseminating catfishes, ovaries and male reproductive systems were exami ned histologically in two species of auchenipterid catfishes, Trachelyopter us lucenai and T. galeatus, from southeastern Brazil. Internal insemination was documented in both species by the presence of sperm within ovaries. Al though there is some variation in gross morphology of the male reproductive systems between the two species, both have four main regions: spermatogeni c lobes, sperm storage regions, and secretory and storage regions of the se minal vesicle. In both species, the anterior portion of the reproductive sy stem is spermatogenic and divided into numerous finger-like lobes. Posterio r to the spermatogenic area is the storage region of the seminal vesicle, a large median structure with a honeycomb-like appearance. This region is co nsistently larger in T. lucenai. Attached to the storage region of the semi nal vesicle in both species are secretory lobes comprised of tubules lined by secretory cells. These lobes in T. lucenai are small and located on the anterior aspect of the storage region of the seminal vesicle, whereas in T. galeatus the lobes are much larger and located laterally. The sperm storag e regions of T. lucenai consist of two large lobes located ventral to the s torage region of the seminal vesicle. Highly compact sperm packets (spermat ozeugmata) fill the lumina of the ramifying tubules of these regions. Each spermatozeugma consists of elongate nuclei tightly arranged parallel to one another. In T. galeatus two distinct sperm storage regions are present. Ju st posterior to the spermatogenic lobes a series of small lobes serve as an terior sperm storage regions. Posterior to the secretory lobes of the semin al vesicle is a series of lobes, at the most posterior aspect of the reprod uctive tract, that serve as posterior sperm storage regions. Both are ident ical, histologically, to the sperm storage regions of T. lucenai. An absenc e of compact spermatozeugmata in the T. galeatus specimens may be related t o variations in their sexual activity. The descriptions presented here allo w for consistent terminology for comparison of regions of the male reproduc tive system based on presumed function. J. Morphol. 246:131-141, 2000. (C) 2000 Wiley-Liss, Inc.