Summary
The present paper demonstrates the ultrastructural differences between the swimbladder of two teleostean fishes with different breathing behavior the jeju a facultative air breathing fish) and the aruanã (exclusively water breathing). Histologically both swimbladders are very similar. Their walls consist of an epithelium, its lamina propria, the muscular sheaths and the adventícia The results suggest that the respiratory adaptations of the jeju swimbladder are characterized by a decreased height of the epithelium in the posterior chamber, the presence of surfactants in the lumen and increased subepithelial vascularization.