Fine structure of chloride cells in freshwater‐ and seawater‐adapted Oreochromis niloticus (Linnaeus) and Oreochromis mossambicus (Peters)

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Abstract
Ultrastructural features of branchial chloride cells in Oreochromis niloticus (Linnaeus) and O. mossambicus (Peters) adapted to both fresh water and sea water were compdred. In freshwater adapted fish of both species chloride cells showed similar morphological features. Multicellular complexes made of a mature chloride cell and one or more accessory cells sharing a single apical crypt have been observed. Whereas high percentages of 0. mossambicus survived at maximum salinity only a few individuals of 0.niloticus showed the capacity to adapt to sea water. In the seawater‐adapted individuals of 0.niloficus and 0. rnossambicusthe chloride cells showed a two‐ and three‐fold increase in sizei. respectively. Most chloride cells are organized in large multi‐cellular complcxcs with apical interdigitations of accessory cells and ‘leaky junctions’. These results indicate that the difference in euryhalinity of the species studied is related to functional rather than structural differences.