Estimation of the proportion of metabolically active mass in the amphipod Gammarus fossarum

Abstract

SUMMARY1. The proportion of metabolically active mass in the freshwater amphipod Gammarus fossarum was determined using different parameters [chemical oxygen demand (COD), total nitrogen (Ntot), total phosphorus (Ptot) and mass of chitinous cuticle].2. The results of linear regressions between body mass and body length, and measured parameters (COD, Ntot, Ptot) show high correlation coefficients for both fresh and the dry animals. The proportion of chitinous mass increased with body size.3. Chemical analysis of Ptot in individuals appears to be the most appropriate parameter for quantitating the metabolically active tissues in animals.4. The dependence of the intensity of electron transport system (ETS) activity per protoplasm, calculated from the Ptot and dry mass of animals, shows that large animals have the same ETS activity per unit of protoplasm as smaller ones.5. We conclude that the chitinous mass is not the only factor which contributes to negative allometry of metabolic activity in G. fossarum.