Most fishery biologists have heard from time to time of experiments on marking fish by tattooing identification marks on them. The present usual methods of marking fish by attaching marks externally to the gill-cover, caudal peduncle, or other part of the body, have the disadvantage that a certain number of the marks are lost, and this uncertainty bedevils all those marking experiments designed to show rates of mortality or rates of capture.

Yet the only reference in the literature known to me is a very short paper by Gandolfi-Hornyold (1929). His most successful experiment consisted in marking six silver eels on the light ventral side withIndian ink (encre de Chine) introduced in the oriental fashion by a bundle of needles. Five of the six fish were alive some 6 weeks later with the marks as clearly legible as when first made. But I know of no further developments of this technique

In August 1939, I made some experiments at the Plymouth Laboratory, by the courtesy of the late Director, Dr Kemp, F.R.S., and with the help of the staff, to all of whom I would express my thanks. Some thirty-two plaice, two soles, and twenty-five rays were placed in one of the big outdoor tanks for the experiments, and were all in good condition, though they had not been fed and were certainly overcrowded

The electric tattooing needle used was bought from a professional tattooist, who also gave me a brief lesson on his art. In principle the needle is a small vibrator run from an ordinary torch battery.