Peixes adultos da espécie Eugerres brasilianus (Gerreidae) tiveram suas brânquias analisadas em microscópio eletrônico de varredura. O epitélio de revestimento é uniforme em todas as porções dos arcos. É formado por células com micropregas concêntricas principalmente nas lamelas primárias e na região faríngea, locais onde são abundantes as células que secretam muco. A caracterização ultra-estrutural das brânquias de E. brasilianus indica que a espécie não é filtradora e que em sua alimentação deve predominar a ingestão de pequenos organismos. Esses resultados estão de acordo com os dados da literatura que determinam o hábito alimentar da espécie através de análises de conteúdo estomacal e outros aspectos.

The gills of the adult fish, Eugerres brasilianus (Gerreidae) were analyzed in a scanning electron microscope. The stratified epithelium was uniform on all parts of the branchial arch. Concentric microridges were present on cells that form this epithelium and were mainly observed in the primary lamellae and pharyngeal region where mucous cells were also abundant. The ultrastructural features of E. brasilianus gills indicated that this was not a filtering species, and that the feeding habit included mainly the intake of small organisms. The results presently obtained agreed with other literature data which determined the feeding habit of this species by means of stomach content analysis and other aspects.

Gills arches of the freshwater fish Prochilodus scrofa Steindachner, 1881 (Lt= 8.0-12.4cm) were removed to be analyzed in a scanning electron microscope. The morphology of the superficial structures of the gill filaments and pharyngeal region of the gills arches was discussed and related to their functional aspects. A great quantity of mucous secretory cells and of microridges, along with the pavement cell surface of the primary lamellae and branchial pharyngeal region, indicate the existence of a protection strategy of the respiratory lamellae. The chloride cells are abundant, specially on the distal portion of the primary lamellae, and bring out the osmo regulatory capacity of this species. This fish seems not to be a filtering one according to: its short and simple gill rakers; presence of several taste buds turned towards the mouth opening; evidence of spines on the external side of the arches and an abundant secretion of mucous in the pharyngeal region. This species probably selects the food to be swallowed through its chemical receptors and retains it with the help of spines and mucous secretion this way protecting the gills filaments against the rubbing of particles over them.

The structure of the spermatozoon of Mugil curema Valenciennes, 1836 was studied using scanning and transmission electron microscopy. The spermatic head is rounded and formed by the nucleus containing granular chromatin, firmly packed resulting in a mass extremely electron dense. The acrossome is absent. The midpiece is characterized by the presence of two centrioles, a plasmatic canal, very few vesicles, and several mitochondria (9-10) with aproximately 0.50µm in diameter. The head and the midpiece are aproximately 1.56µm in diameter. The flagellum conforms to the 9 + 0 flagellar pattern near the transition region in its midpiece and is 9 + 2 from there on up to the distal region of the axoneme. The electron density in the A tubules 1, 2, 5 and 6 shows the asymetry of this spermatozoa. Its spermatic cell differs ultrastructuraly from those of other Mugilidae species mainly because it has the highest number of mitochondria.