Sublethal effects of copper on the freshwater crab Potamonautes warreni

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 mg Cu l(-1) (15.75 micromol l(-1)). Under control (non-copper-exposed) conditions M (O(2)) M(b)(-1) was 35.7+/-8.5 micromol kg(-1)min(-1) (mean+/-S.D.), M (NH(4)-N) M(b)(-1) 2.92+/-0.26 micromol kg(-1)min(-1) and M (CO(2)) M(b)(-1) 25.6+/-9.0 micromol 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 mg Cul(-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.