Effects on growth and survival of retention of rod‐caught cyprinids in large keepnets

Abstract

The long‐term (about 2 months) mortality and the growth of five species of cyprinids retained and not retained in large keepnets (490 L, 2.5 mm mesh, knotless netting) were determined in drainable ponds. All experiments were carried out at least in duplicate. No statistically significant difference was found in mortality and growth between fish that were kept in the keepnets and fish that did not undergo this treatment. Differences in growth and mortality were related to fish species and season. No effect of retention time in the keepnet on mortality and growth was observed. No statistically significant difference in mortality and growth was found between bream, Abramis brama (L.), captured by anglers and the controls. Also, no differences were found in mortality and growth of rod‐caught bream retained in keepnets and rod‐caught bream that did not undergo this treatment. No statistically significant effect of lifting of the keepnets could be determined. Based on the available evidence, it was concluded that the holding of rod‐captured cyprinids in a small keepnet may cause temporary adaptations to the behaviour and physiology of the fish. Depending on the type and size of the keepnet, the material and the mesh of the netting, loss of scales and secretion of mucus may take place. The data from experiments with large keepnets do not show irreversible changes, leading to decreased fitness and ultimately to death of the cyprinids.