Oxygen consumption, ammonia excretion and osmoregulation of callinectes similis Juveniles (Crustacea: Portunidae) exposed to fluctuating salinities
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Abstract
The oxygen consumption of Callinectes similis was determined under salinity fluctuations. The metabolic rate remained unchanged (P > 0.05) and within a metabolic range of 1.23 to 2.08 mg O2.h–l.g–l D.W., exhibiting a type IV response according to Kinne (1971). Ammonia excretion rose significantly to 0.028 mg N-NH4.h–l.g–l D.W. (P < 0.05) as the salinity decreased from 35 to 24‰; in a salinity range of 18-12-18‰ it remained unchanged at 0.021 mg N-NH4.h–l.g–l D.W. It increased at 26‰to 0.029 mg N-NH4.h–l.g–l D.W. and there was a minimum value of 0.012 mg N-NH4.h–l.g–l D.W. at 35‰. The O:N atomic ratio calculated for C. similis indicates that the crabs were not significantly affected (P > 0.05) by osmotic stress. In high salinities catabolism is based on carbohydrates and in lower salinities on a mixture of lipids and carbohydrates. The osmoregulatory pattern exhibited by C. similis is of an osmoconforming organism, the hemolymph was only slightly hyperosmotic in higher and isosmotic in lower salinities.
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