HEMOLYMPH VOLUME, CHANGES IN BIOCHEMICAL COMPOSITION OF BLOOD, AND CYTOLOGICAL RESPONSES OF DIGESTIVE CELLS IN MYTILUS-CALIFORNIANUS CONRAD, INDUCED BY NUTRITIONAL, THERMAL AND EXPOSURE STRESS

1. The volume of the extracellular space in Mytilus californianus is 46% of the wet weight of the tissues (excluding the shell). 2. Fluid lost through bleeding is replaced within four hours, and both the dissolved and the cellular components (haemocytes) of the haemolymph are quickly restored. 3. The level of ammonia in the plasma increases when starved mussels begin to feed. This is a result of the specific dynamic action (SDA) which is associated with protein metabolism during feeding. 4. Ammonia accumulates in the plasma when mussels are exposed to air, which indicates that catabolism of nitrogenous substrates continues when the animal is exposed at low tide. 5. There are few changes in plasma carbohydrate, lipid and protein levels which are attributable to exposure, ration or increased temperature, suggesting good short-term regulation. 6. Lysosomal intracellular digestion continues in the digestive cells of mussels exposed to air. During exposure, there is also an increase in the numbers of circulating haemocytes, which may be associated with the continuation of the digestion process. 7. At high ration and elevated temperature, the digestive epithelium thickens, and there is some evidence that the rate of lysosomal intracellular digestion increases. During periods of starvation the epithelium becomes thinner and there is a loss of cytoplasm, probably by autophagy. © 1978 Springer-Verlag.