Acute and sub-chronic effects of sub-lethal cadmium exposure on energy metabolism in the freshwater shrimp, Paratya curvirostris.

Cadmium (Cd) is a toxic trace element enriched in waters through activities such as mining and agriculture. The freshwater shrimp Paratya curvirostris inhabits near-coastal, lowland streams potentially impacted by Cd, but nothing is known regarding its sensitivity to this metal. An acute (96h) median lethal concentration (LC) of 405µgL was derived for P. curvirostris, placing it among the most tolerant of freshwater shrimp species. Acute (4 d; 0, 50 and 100µgL) and sub-chronic (10 d; 0, 25 and 50µgL) exposures then investigated effects of Cd on energy metabolism (respiration rate, excretion rate, O:N ratio). In contrast to effects in previously studied species, Cd induced an increased respiration rate, which when coupled with an unchanged excretion rate, resulted in an increased O:N ratio. These data were explained by an increased reliance on carbohydrate and/or lipid as a metabolic substrate stimulated by increased metabolic costs of toxicant exposure. Similar effects were seen across all time-points, although the lowest effective Cd concentration decreased with increased exposure time. Overall, results suggest that Cd is unlikely to be a significant environmental stressor to P. curvirostris, except in highly contaminated freshwaters, and/or where Cd co-occurs with hypoxia.