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

Abstract

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 1n27 to 2n46 µm, 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 8n10 µm (dorsal zone of gill 8) both in hyper-and hyposaline media compared with seawater. The dark areas measured in gill 8 treated with AgNO $ 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.

Active NaCl absorption across posterior gills of hyperosmoregulatingChasmagnathus granulatus

“…When the animals were adapted from seawater to brackish water, the thickness of the posterior gill epithelium increased (Genovese et al, 2000), indicating its involvement in osmoregulatory active NaCl absorption, as observed in a variety of Crustacea (Péqueux et al, 1988). Recently, a ouabain-sensitive net influx of Na + was determined with isolated and perfused posterior gills (Luquet et al, 2002).…”

“…The thickness of the posterior gill epithelium increases when the animals are adapted to either low or high salinities, suggesting the involvement of the gills in salt absorption of hyperosmoregulating crabs and in salt secretion in hypo-osmoregulating animals (Genovese et al, 2000). In a recent study with perfused posterior gills, the respective active transbranchial absorption and secretion of Na + have been directly demonstrated (Luquet et al, 2002); however, a satisfying analysis of the transport mechanisms is still lacking.…”

Cytochemical characterization of gill and hepatopancreatic cells of the crab Ucides cordatus (Crustacea, Brachyura) validated by cell metal transport

“…Therefore, these cells are not involved with respiration or ionic transport, because of the imperceptible presence of mitochondria in its interior (Leise, 1996). On the other hand, in a study developed by Genovese et al, 2000 andFreire et al (2007), there is a suggestion that pillars cells can help in ionic transport besides the respiration process.…”

“…The crustacean gills, apart from gas exchange, are responsible for other functions such as acid basic balance, ammonia excretion, ionic exchange and osmoregulation (Genovese et al, 2000;Freire et al, 2008). To perform these processes, specific cells for each function are found: (1) Pillar cells that are important in gill support; (2) Thick or Ionocytes cells that perform osmoregulation and ionic exchange; (3) Thin cells that are important for respiration and (4) Haemocytes, responsible for coagulation and encapsulation of toxics agents in the organism (Lawson et al, 1995;Freire et al, 2008;orteGa et al, 2011).…”

Osmoregulation in the Hawaiian anchialine shrimpHalocaridina rubra(Crustacea: Atyidae): expression of ion transporters, mitochondria-rich cell proliferation, and hemolymph osmolality during salinity transfers

“…3B,C) showed a statistically significant increase in total area stained from 59% in 32‰ to 72% in 2‰ (Student's unpaired t-test, P=0.003). In contrast, AgNO 3 staining never exceeds more than 30% of the total lamellar surface area for the moderate osmoregulator C. maenas (Compere et al, 1989), and for strong osmoregulators, AgNO 3 staining went from 35% of the lamellae in the osmoregulating gills to 52% during transfer from SW to 12‰ for C. granulatus (Genovese et al, 2000) and increased 4-fold during low salinity transfer for C. sapidus (Neufeld et al, 1980). Thus, the increased staining seen in gill 4 of H. rubra suggests either a fairly weak response to salinity changes or, more likely, that the MRC population is already at or near its maximum and large increases are not possible.…”