Comp. Biochem.Physiol. Vol. 106B,No. 3, pp. 747-753, 1993 0305-0491/93$6.00+ 0.00 Printed in Great Britain © 1993PergamonPress Ltd CARBOHYDRATE METABOLISM DURING OSMOREGULATION IN CHASMAGNATHUS GRANULATA DANA, 1851 (CRUSTACEA, DECAPODA) L. E. M. NERY and E. A. SANTOS Departamento Ci~ncias Fisiol6glcas, FundacSo Universidade do Rio Grande, Cx. Postal 474, Rio Grande--RS, 96-201-900, Brasil (Received 23 February 1993; accepted 26 March 1993) Abstract--1. Since glucose is one of the main energetic substrates for general metabolic processes in crustaceans, analysis of carbohydrate levels can furnish information on the energy metabolism of intact animals during osmoregulation. 2. Different groups of Chasmagnathusgranulata were transferred to different salinities(0 and 40%o),and the glucose and glycogen concentrations in blood, gills, muscle and bepatopancreas were determined at the beginning of the experiment and 24, 72, 168 and 360 hr after the salinity changes. 3. Differencesin tissues carbohydrate levels were observed between summer and winter, that reflected differences in reserve mobilization. 4. In the summer, hypo- and hyperosmotic shocks induced an increase in carbohydrate levelsin almost all tissues studied, indicating gluconeogenesis. 5. In the winter, a carbohydrate mobilization occurred only in the gills and hepatopancreas after both osmotic shocks. 6. Thus, the substrate reserve used for energy production required for osmoregulation seems to be dependent on the season and tissues. INTRODUCTION The ability to cope with osmotic stress in media with a fluctuating salinity regime is an essential requisite for the successful settlement of a population in such a habitat (Gilles, 1982). Euryhaline crustaceans employ two types of general osmoregulatory mechan- isms: (1) anisomotic regulation of the extracellular fluid; and (2) isosmotic regulation of the intracellular fluid (Gilles and Pequeux, 1983). It is clear that such mechanisms may modify the animal's energy during adaptation to a new salinity. Most of the studies on the relationship between energetic cost and osmoregulation in intact animals have been based on oxygen consumption measure- ments. Kinne (1964) described four types of respirat- ory responses to salinity changes: (1) the respiratory rate increases in subnormal and/or decreases in supranormal salinities; (2) the rate increases in sub- and supranormal salinities; (3) the rate decreases in sub- and supranormal salinities; and (4) the rate remains essentially unaffected. Types 1 and 2 are largely represented by euryhaline crustaceans. In type 3, no crustaceans were cited, and type 4 is represented by extremely euryhaline forms. However, these changes in respiratory rates may reflect a number of physiological alterations other than osmoregulation (Vernberg, 1983). In this case, they may reflect behav- ioral changes rather than the effect of salinity on basic metabolic processes. Potts (1954) used another approach to relate energetic metabolism to osmoregulation. This author estimated the metabolic cost of osmotic regulation for animals in fresh water (Eriocheir sinensis) based on thermodynamic considerations, taking into ac- count only anisosmotic regulation of the extracellular fluid in animals acclimated for a long time. One way of verifying changes of the energetic metabolism of intact animals during osmoregulation is to analyze eventual modifications in energetic substrates. This method has not been frequently employed. Since glucose is one of the main energy substrates for general metabolic processes in crus- taceans (Hu, 1958), it is possible that an adaptation of the carbohydrate metabolism could take place during osmoregulation. Even though carbohydrate metabolism has been relatively well studied, only recently have studies on alterations of glucose and glycogen levels of intact animals during osmoregulatory efforts been under- taken (Lacerda and Sawaya, 1983; Santos and Nery, 1987; Spaargaren and Hafner, 1987). These exper- iments have shown that glucose levels change signifi- cantly in extreme salinities. Our studies were undertaken to determine, through measurements of glucose and glycogen concen- trations in blood, gills, muscle and hepatopancreas, the carbohydrate metabolism alteration during osmo- regulatory processes over relatively large periods of time in an estuarine crab, Chasmagnathus granulata. This species was considered by Mafie-Garzon et al. (1974) to be an excellent osmoregulator (hypo- and hyper-regulator). 747