Morphological organization of the male brood pouch epithelium of Syngnathus abaster Risso (Teleostea, Syngnathidae) before, during, and after egg incubation.

The morphological organization of the male brood pouch epithelium of Syngnathus abaster, before, during, and after the breeding period, was observed by light and electron microscopy. Before gestation, the epithelium of the pouch wall was compact and consisted of three kinds of cells: typical epithelial cells (pavement cells), mitochondria-rich cells (MR cells), and, presumably, differentiating MR cells. In this stage, very few capillaries were observed beneath the epithelium. During egg incubation, the capillaries increased in number and size, large intercellular spaces formed among epithelial cells at their basal sides, MR cells were abundant, and differentiating MR cells were only occasionally observed. After incubation, MR cells degenerated by necrosis and apoptosis. The intercellular spaces between the epithelial cells disappeared and the number and size of the capillaries beneath the epithelium decreased. The presence of MR cells during gestation and their degeneration after incubation suggest that these cells play a pivotal role in the physiological functions of the brood pouch. The similar cytological characteristics of syngnathid pouch MR cells and chloride cells of the teleostean gills suggests that the Syngnathidae brood pouch is involved in osmoregulation of the fluid surrounding the developing embryos.