Ionic regulation of blood and gastric fluid in crustacea decapoda (Carcinus maenas, Cancer pagurus, Maia squinado) : the role of the foregut

Tentori, Ernestina (1988) Ionic regulation of blood and gastric fluid in crustacea decapoda (Carcinus maenas, Cancer pagurus, Maia squinado) : the role of the foregut. University of Southampton, Doctoral Thesis.

Abstract

In crustaceans the exchange of water and salts between the organism and the medium has been linked mainly with the activity of the gills and the antennal glands. By contrast a generalization of the role of the gut in these processes has been difficult to define. This is understandable since there is a tendency to study intermoult individuals of highly specialized forms that inhabit environments of extreme salinities. However, the process of moulting affects crustaceans in any aquatic environment and produces disequilibrium of the body fluids composition. This problem surely involves the action of every ion-regulative mechanism developed by the animal. In the present study the foregut of decapods was studied as a possible site of ionic regulation of body fluids during the moult cycle. One estuarine (Carcinus maenas), and two marine (Cancer pagurus and Maia squinado) species were studied. Ionic concentrations of blood and gastric fluid, permeability to water across the foregut wall and drinking rates were evaluated. In the three decapods, a cyclic pattern, developing parallel to the moult cycle, was evident in these parameters, indicating that the gastric fluid `lq circulation and ionic composition are critically controlled by the animal, and that the changes taking place in this fluid are likely to affect the ionic regulation of blood. `lq In vitro experiments of ionic permeability of the foregut wall and `lq in vivo responses to salinity variations demonstrated that the regulation of Na⁺, Ca⁺⁺ and Mg⁺⁺ in blood and gastric fluid are independent mechanisms. Besides these physiological characteristics, the foregut wall was observed to have certain similarities with transporting epithelia, as well as cyclic modifications of the intracellular organization related to the moult, that had not been reported before for other types of crustacean integuments. It is concluded that the foregut, reflected as gastric fluid changes, takes part in the regulation of blood ionic composition during the moult cycle, its greatest activity being at time of ecdysis. The analyses performed indicate that there is a range of responses from marine species (M. squinado) with minimal ability for ionic regulation, to estuarine species (C. maenas) with a degree of euryhalinity. C. pagurus showed a transitional potential between these two species. The relevance of the suggested diversity of adaptative mechanisms within the stenohaline marine species is discussed in relation to the present day approach to the study of osmotic and ionic regulation. (DX88857)

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