BRANCHIAL CHLORIDE CELLS IN LARVAE AND JUVENILES OF FRESH-WATER TILAPIA OREOCHROMIS-MOSSAMBICUS

Branchial chloride cells in the developing larvae and juveniles of fre shwater tilapia, Oreochromis mossambicus, were identified and the memb rane Na+/K+-ATPase was localized in situ through binding of the fluore scent dye anthroylouabain. After co-labelling of the cells with the fl uorescent probes DASPMI and Con-A-FITC, the mitochondria and apical cr ypt in the same chloride cells were visualized using confocal laser sc anning microscopy, The high density of apical crypts indicated that ma ny chloride cells were functional, The density of branchial chloride c ells in larvae 10 days after hatching was approximately 6000 mm(-2). A n extremely high Na+/K+-ATPase specific activity of approximately 1500 mu mol P(i)h(-1)mg(-1) was measured in the gills 10 days after hatchi ng, With the development of secondary lamellae and hence an increase i n the amount of branchial epithelial protein, a concomitant decrease i n the specific activity of the enzyme in the gill tissues was observed . Total Na+/K+-ATPase activity increased markedly in the early life st ages, Our data indicate that in larval stages of fish the gills form a functional ionoregulatory organ before they start functioning as a ga s-exchange organ.