Sublethal effects of copper on the freshwater crab Potamonautes warreni

Abstract

The mass specific rates of oxygen consumption ( M ̇ O 2 M b −1), ammonia excretion ( M ̇ NH 4–N M b −1) and carbon dioxide production ( M ̇ CO 2 M b −1) were measured after 7, 14 and 21 days exposure of adult Potamonautes warreni to a sublethal concentration of 1.0 mgCu l −1 (15.75 μmol l −1). Under control (non-copper-exposed) conditions M ̇ O 2 M b −1 was 35.7±8.5 μmol kg −1 min −1 (mean±S.D.), M ̇ NH 4–N M b −1 2.92±0.26 μmol kg −1 min −1 and M ̇ CO 2 M b −1 25.6±9.0 μmol kg −1 min −1. The oxygen:nitrogen (O:N) ratio and respiratory quotient (RQ) were 24.5±3.0 and 0.80±0.06, respectively. M ̇ O 2 M b −1 of copper-exposed crabs showed a significant increase after 7 and 14 days, but decreased significantly by 40% after 21 days. From the increased O:N ratio and RQ below 0.7, it is clear that crabs exposed to 1 mgCu l −1 metabolize lipids during the entire 21-day exposure period. Free fatty acids in the midgut gland were determined by GC-MS, and showed increases of up to 600% in some C14 to C18 fatty acids. It is proposed that the excess lipids inhibit the pyruvate dehydrogenase complex, leading to the acceleration of the gluco- and glyco-neogenic pathways. Increased glyconeogenesis results in elevated glycogen concentrations in all tissues after 21 days. Experiments on acutely exposed P. warreni show increased incorporation of 14C-labelled lactate into glycogen.