Growth, mortality and tag retention of small Anguilla anguilla marked with visible implant elastomer tags and coded wire tags under laboratory conditions

P>Growth, and potential marking-related mortality of small European eel Anguilla anguilla (L.) after marking with visible implant elastomer tags (VIE) and coded wire tags (CWT) were investigated over a 6-month period in a laboratory experiment. In addition, mark retention after marking was examined for another 16.5 months. Neither marking method had a significant effect on growth (P > 0.05) or mortality (P > 0.05). After 32 days detection of the VIE marks implanted on the ventral surface and along the base of the ventral tail fin margin was 98 and 100%, respectively, but decreased to 9 and 66% after 512 days. Retention of the CWT implanted in the dorsal musculature of A. anguilla was 99% after 32 days and did not change by day 512. It was therefore concluded that marking-induced mortality was nil for both marking types over the 6-month period. Generally, both methods are found to be suitable for marking young A. Anguilla. VIE tags, however, should be used for short-time mark-recapture experiments only, and should be injected at the base of the ventral fin margin. The use of CWTs seems to be the more suitable marking method for long-term mark-recapture experiments. Nevertheless, field tests are necessary to evaluate these marking methods.