Gills of the medaka (Oryzias latipes): A scanning electron microscopy study
Résumé
The general morphology and surface ultrastructure of the gills of adult and larvae medaka (Oryziaslatipes) were studied in freshwater and seawater using scanning electron microscopy. The gills ofall examined fish were structurally similar to those of other teleosts and consisted of four pairs ofarches supporting (i) filaments bearing lamellae and (ii) rakers containing taste buds. Three celltypes, specifically pavement cells, mitochondria-rich cells (MRCs), and mucous cells, constitutedthe surface layer of the gill epithelium. Several distinctive characteristics of medaka gills werenoted, including the presence of regularly distributed outgrowth on the lamellae, enlarged filamenttips, the absence of microridges in most pavement cells in the filament and lamellae and the presenceof MRCs in the arch at the filament base. A rapid mode of development was recorded in thegills of larval fish. At hatching, the larvae already had four arches with rudimentary filaments,rakers, and taste buds. The rudimentary lamellae appeared within 2 days after hatching. Theseresults suggest the early involvement of larval gills in respiratory and osmoregulation activities. Theresponses of the macrostructures and microstructures of gills to seawater acclimation were similarin larvae and adult fish and included modification of the apical surface of MRCs, confirming theimportance of these cells in osmoregulation. The potential roles of these peculiarities of the macrostructuresand microstructures of medaka gills in the major functions of this organ, such asrespiration and osmoregulation, are discussed.