EFFECT OF MORPHOMETRIC MATURITY AND SIZE ON ENZYME-ACTIVITIES AND NUCLEIC-ACID RATIOS IN THE SNOW CRAB CHIONOECETES-OPILIO

Indicators of metabolic capacity and the potential for protein synthes is in male snow crabs, Chionoecetes opilio, were measured to estimate how these factors are affected by morphometric maturity and body size. The metabolic capacity of muscle, as depicted by cytochrome C oxidase (CCO), citrate synthase (CS), and lactate dehydrogenase (LDH) activit y, was greater in adults than in adolescents, while that of the digest ive gland was not affected by maturity. These differences may reflect the different locomotory habits of adults and adolescents. Indicators of the potential for protein synthesis, the RNA:DNA and protein:RNA ra tios, did not differ between adult and adolescent crabs, presumably be cause the animals were in late intermolt stage and flesh growth was al ready completed. The total mass of muscle, as estimated by the flesh c ontent of the merus, and the total capacity of muscle CCO scaled isome trically with body mass, while that of CS scaled with an exponent <1. The mass of the digestive gland, as well as the total capacity of both mitochondrial enzymes in this organ, increased more slowly than body size. These results support the hypothesis that the negative allometry generally observed for aerobic metabolism may be caused by the decrea sing size of the metabolically most active tissues with an increase of body mass. In contrast with the positive allometry of the anaerobic c apacity of fast-swimming fish with body mass, we noted an isometric re lationship between these two variables in the rather slow-moving C. op ilio. This supports the hypothesis that an enhanced anaerobic capacity is necessary for the largest individuals of a fast-moving species in order to maintain their burst swimming speed despite the increased fri ction generated by increased speed and body size.