Effects of Cyprinus carpio on Potamogeton pectinatus in experimental culture: the incidence of the periphyton

The effect of one-year-old common carp (Cyprinus carpio L.) on plants and s eedlings of Potamogeton pectinatus L., and on periphyton development was st udied in 100 l glass aquaria. Two 30-day experiments were conducted using a muddy sediment or a pebbly bottom. In both cases, three treatments based o n different fish size (two fish/aquarium) were assayed. The control had no fish. In both experiments, chlorophyll content of the periphyton increased from the beginning to the end of the period, for the three fish treatments. Light attenuation by periphyton was high, with final values 12-30% higher than in the control. Periphytic communities acclimated to reduced light con ditions when the bottom was muddy. It can be concluded that, in muddy condi tions, small carp affected plant growth by shade stress, which is achieved by a combination of increase in turbidity and the developing of a leaf peri phytic cover. Under pebbly conditions, plant damage was caused by collision s and the growth of epiphytic algae. Medium and large fish consumed plants in both experiments. Seedlings were affected by herbivory in all cases.