Effects of water-borne copper on digestive and metabolic enzymes of the giant freshwater prawn Macrobrachium rosenbergii

The aim of the present study was to evaluate the potential utility of enzyme parameters as indicators of water-borne copper (Cu²⁺) contamination in the giant freshwater prawn Macrobrachium rosenbergii. Activities of the digestive enzymes of tryptase, pepsin, cellulase, amylase, and metabolic enzymes of alkaline phosphatase (AKP), acid phosphatase (ACP), superoxide dismutase (SOD) and glutathione-S-transferase (GST) were measured in the hepatopancreas of M. rosenbergii after 7 days of exposure to copper (Cu ²⁺) concentrations ranging from 0.01 mg/L to 0.5 mg/L. A significant inhibition on the digestive enzymes by Cu²⁺ was observed, being relevant to the elevated Cu²⁺ concentration. The maximum inhibition rate was recorded in amylase among all the digestive enzymes. As regards the metabolic enzymes, although the activity of SOD had an increase in final copper treatment groups when comparing to the controls, those of ACP and AKP significantly decreased in accordance with increase in Cu²⁺ concentrations. In addition, though there was a significantly decreased GST activity in group treated with 0.01 mg/L Cu²⁺; the activity could increase gradually in the prawns when exposed to higher Cu²⁺ concentrations. The responses of the metabolic and digestive enzymes in the hepatopancreas of M. rosenbergii were sensitive to water-borne copper contamination; furthermore, amylase, and GST seem to be most suitable biomarkers of environmental Cu²⁺ stress in M. rosenbergii.