Acute and chronic effects of cadmium on blood homeostasis of an estuarine crab, Chasmagnathus granulata, and the modifying effect of salinity.

Whole body oxygen consumption and some hemolymph parameters such as pH, partial pressure of gases, level of ions and lactate were measured in the estuarine crab Chasmagnathus granulata after both acute (96 h) and chronic (2 weeks) exposure to cadmium at concentrations ranging from 0.4 to 6.3 mg/l. In all instances, the crabs developed hemolymph acidosis, but no respiratory (increased PCO2) or lactate increases were evident. Hemolymph levels of sodium and calcium were always increased by cadmium exposure. The chronic toxicity of cadmium was enhanced at 12 per mil salinity, even causing a significantly higher mortality in comparison with the higher salinity (30 per mil ) used. A general metabolic arrest took place at 12 per mil salinity in the crabs chronically exposed to cadmium, as indicated by decreases of oxygen consumption and PCO2, an increase of PO2, along with no changes in lactate levels. These imbalances were associated with severe necrosis and telangiectasia in the respiratory gills, probably leading to respiratory impairment and finally histotoxic hypoxia and death of the animals.

Acute and chronic effects of cadmium on blood homeostasis of an estuarine crab, Chasmagnathus granulata, and the modifying effect of salinity

Whole body oxygen consumption and some hemolymph parameters such as pH, partial pressure of gases, level of ions and lactate were measured in the estuarine crab Chasmagnathus granulata after both acute (96 h) and chronic (2 weeks) exposure to cadmium at concentrations ranging from 0.4 to 6.3 mg/l. In all instances, the crabs developed hemolymph acidosis, but no respiratory (increased PCO2) or lactate increases were evident. Hemolymph levels of sodium and calcium were always increased by cadmium exposure. The chronic toxicity of cadmium was enhanced at 12 0/00 salinity, even causing a significantly higher mortality in comparison with the higher salinity (30 0/00) used. A general metabolic arrest took place at 12 0/00 salinity in the crabs chronically exposed to cadmium, as indicated by decreases of oxygen consumption and PCO2, an increase of PO2, along with no changes in lactate levels. These imbalances were associated with severe necrosis and telangiectasia in the respiratory gills, probably leading to respiratory impairment and finally histotoxic hypoxia and death of the animals

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 changing 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 were studied by means of morphological and morphometric analysis, and immunohistochemical identification of cell proliferation (BrdU technique). In anterior (1-3) gills the epithelium thickness from crabs acclimatised to 12, 34 and 44 g/l ranged from 1.27 to 2.46 microm, with no significant change during acclimatisation, thus denoting a respiratory function. Medial (4-5) gill epithelium was slightly thicker in extreme salinities, but these differences were not statistically significant. In contrast, epithelial thickness of the posterior (6-8) gills increased significantly up to 8.10 microm (dorsal zone of gill 8) both in hyper- and hyposaline media compared with seawater. The dark areas measured in gill 8 treated with AgNO3 revealed putative ion transporting 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 almost never occurred in the gills/salinity combinations studied during the initial 48 h of transfer from seawater to hyperconcentrated or diluted media, thus suggesting an increase in cell size rather than cell proliferation.

Bimodal breathing in the estuarine crab Chasmagnathus granulatus Dana 1851--physiological and morphological studies.

Chasmagnathus granulatus is an estuarine crab which actively moves from subtidal to supratidal areas. To elucidate the possible existence of extrabranchial sites for aerial gas exchange, we measured respiratory and acid-base variables in animals with and without branchial water (controls and experimental crabs, respectively) during air exposure. An histological study of the branchiostegite was also performed. Throughout 4 h of emergence C. granulatus did not suffer venous hypoxia, even without branchial water. The rate of oxygen uptake (M(O(2))) was similar in both groups. The rate of carbon dioxide excretion (M(CO(2))) and the gas exchange ratio (R) significantly decreased during emergence in both groups, with R significantly lower for experimental crabs. Consequently, CO(2) was accumulated in the hemolymph. This variable stabilized after 90 min in control animals, but experimental crabs continued accumulating CO(2). Histological study of the branchiostegites demonstrated the presence of an attenuated and greatly perfused epithelium facing the branchial chamber lumen, with a shortest diffusion distance of 0.5 microm. Simple folds and lobulated projections increase the respiratory surface area. These results suggest that C. granulatus is a bimodal breathing crab, active both in water and air. When emerged, this species extract oxygen directly from air through branchiostegal lungs, but relies on branchial exchange to eliminate carbon dioxide.