SCALING OF CALCIUM, INORGANIC CONTENTS, AND ORGANIC CONTENTS TO BODY MASS DURING THE MOLTING CYCLE OF THE FRESH-WATER CRAYFISH PROCAMBARUS CLARKII (GIRARD)

Abstract

Allometric relationships were derived for calcium, inorganic contents, and organic contents of the crayfish Procambarus clarkii (0.012-33 g) at various stages in the molting cycle. Whole body parameters were measured at intermolt, ecdysis, and postmolt (1 week); determinations were also made on shed exuviae and gastroliths. Significant linear relationships on log-transformed data were obtained for all parameters. Scaling exponents for mineral content varied from 0.93-1.27, agreeing closely with scaling of supportive tissue mass in a range of species possessing both exo- and endoskeletons. Regression relationships were interpolated for hypothetical 1-and 30-g crayfish. Larger crayfish demineralize their cuticle more effectively prior to ecdysis; even so, exuviae constitute an avenue for significant mineral loss (30 cf. 50%). They also store less mineral between molts, excreting increasing amounts into the external water. Gastroliths are the major form of mineral storage especially in small crayfish (74 cf. 57%). Large postmolt crayfish are more mineral deplete (15%) than small crayfish (35%). Within 1 week of postmolt, 1-g crayfish have surpassed intermolt mineral content, by branchial uptake from external water. Their rapid rate of remineralization is commensurate with their increased molting frequency. In the same time period, larger crayfish have recovered only 30% of their intermolt mineral content. Continued branchial uptake, together with ingestion of shed exuviae or other food sources, would restore mineral balance. Irrespective of size, crayfish lose 15% organic matter in the exuviae at ecdysis. In the absence of food, postmolt crayfish draw on organic reserves for energy.