Change in riverine epilithic extracellular enzyme activity in response to fish farm effluent.

Extracellular aminopeptidase and phosphatase activity was measured at the surfaces of submerged stones collected from a river upstream and downstream of a fish farm discharge. Aminopeptidase activity was largely indifferent to the discharge. Phosphatase activity, in contrast, was depressed downstream of the outfall. Thus, there was no evidence of enhanced epilithic extracellular enzyme activity to facilitate biopurification downstream of the fish farm discharge.