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The Journal of Experimental Biology 205, 167-175 (2002)
© 2002 The Company of Biologists Limited

Hyperosmoregulation in the red freshwater crab Dilocarcinus pagei (Brachyura, Trichodactylidae): structural and functional asymmetries of the posterior gills

Horst Onken^* and John Campbell McNamara

Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto 14040-901, São Paulo, Brasil

*e-mail: onkenh{at}ffclrp.usp.br

Accepted 24 October 2001

The osmotic and ionic status of the haemolymph and the structural and ion-transport characteristics of the posterior gills of Dilocarcinus pagei, a hololimnetic crab, were investigated. Haemolymph osmolality was 386±18 mosmol kg^–1, while [Na⁺] and [Cl^–] were 190±13 and 206±12 mmol l^–1, respectively; [K⁺], [Ca²⁺] and [Mg²⁺] were 9.7±0.7, 10.2±0.5 and 2.8±0.4 mmol l^–1, respectively (means ± S.E.M., N=12–17). The gill lamellae possess a central, osmiophilic area, which exhibits a marked structural asymmetry. The thick (18–20 µm) proximal epithelium is characterised by basal invaginations and a few apical vesicles, while the thin (3–10 µm) distal epithelium consists of apical pillar cell flanges populated by vesicles and membrane invaginations. Isolated gills, bathed and perfused with NaCl saline, spontaneously generate a negative transbranchial potential difference (V_te), which stabilises at positive or negative values. Ouabain shifts V_te to more positive values. When mounted in an Ussing chamber, distal split lamellae generate a negative, Cl^–-dependent short-circuit current (I_sc). Na⁺ substitution leads to more negative values of I_sc. Internal ouabain is without effect, while diphenylamine-2-carboxylate and acetazolamide abolish I_sc. Proximal split lamellae show a positive, Na⁺-dependent I_sc, which decreases after internal application of ouabain. These data suggest that the thin epithelium actively absorbs Cl^–, while the thick epithelium actively absorbs Na⁺.

Key words: Crustacea, red freshwater crab, Dilocarcinus pagei, haemolymph, osmolality, ion concentration, gill, transbranchial potential difference, split gill lamellae, Ussing chamber, short-circuit current.

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