The morphometric changes in the gills of the estuarine crab Chasmagnathus granulatus under hyper- and hyporegulation conditions are not caused by proliferation of specialised cells

Chasmagnathus granulatus is a hyper-hyporegulating crab that inhabits chang ing habitats of salinity in Brazil, Uruguay and Argentina. Since the gills are the main sites for active ion transport in crabs, the adaptive changes in the gill epithelium occurring under different conditions of salinity wer e studied by means of morphological and morphometric analysis, and immunohi stochemical identification of cell proliferation (BrdU technique). In anter ior (1-3) gills the epithelium thickness from crabs acclimatised to 12, 34 and 44 g/l ranged from 1.27 to 2.46 mu m, with no significant change during acclimatisation, thus denoting a respiratory function. Medial (4-5) gill e pithelium was slightly thicker in extreme salinities, but these differences were not statistically significant. In contrast, epithelial thickness of t he posterior (6-8) gills increased significantly up to 8.10 mu m (dorsal zo ne of gill 8) both in hyper- and hyposaline media compared with seawater. T he dark areas measured in gill 8 treated with AgNO3 revealed putative ion t ransporting tissue, especially at 12 and 44 g/l? corresponding to the zones of higher epithelial thickness. Hence these areas seem to participate both in hyper- and hyporegulation. Proliferating cells labelled with BrdU almos t never occurred in the gills/salinity combinations studied during the init ial 48 h of transfer from seawater to hyperconcentrated or diluted media, t hus suggesting an increase in cell size rather than cell proliferation.