The dependence on temperature and pH of the effects of zinc and copper on proteolytic activities of the digestive tract mucosa in piscivorous fish and their potential preys.

The dependence of the effects of zinc and copper on the activities of proteinases of the stomach and intestinal mucosa on temperature and pH in four species of boreal piscivorous fish (pike Esox lucius, zander Zander lucioperca, perch Perca fluviatilis and burbot Lota lota) as well as in some of their potential preys (kilka Clupeonella cultriventris, ruff Gymnocephalus cernuus, perch and roach Rutilus rutilus) was investigated. Species-specific differences of the effects of these heavy metals upon the activities of proteinases depending on temperature and pH were demonstrated. It was revealed that the stomach mucosa proteinases were more tolerant to the effects of the studied factors than the intestinal mucosa proteinases, especially true for pike. The effects of the heavy metals on the whole body proteinases of the fishes' potential preys were mostly dependent on temperature than on pH. At pH 3.0, the negative action of zinc and copper on the fish digestive tract mucosa proteolytic activity to a considerable degree was compensated by the high activity of the hemoglobinlytic proteinases, probably, cathepsine D.