Abnormal pigmentation in flatfish may be a useful tool in the study of populations. Since 1963 its merits as a population character have been investigated in the plaice of the central and southern North Sea. In this plaice stock the existence of at least four separate populations had been demonstrated already by means of meristic and otolith features and tagging experiments. In general, the results obtained with abnormal pigmentation confirmed what had been found before, but in some instances more detailed information could be obtained e.g. on recruitment. Moreover the use of pigment anomalies opens possibilities in assessing natural mortality rates in pre-recruit plaice from different nurseries. The results obtained are in contradiction with the hypothesis generally held, that pigment deficiencies are innate or develop during or before metamorphosis only. It was found that in one class of abnormal pigmentation a trematode worm living in cysts in the skin of juvenile plaice is responsible for the development of pigment anomalies. |
