The systematic history of the Mediterranean centracanthid fishes is reviewed and the past and present nomenclatural confusion in this group, most of which appears to have been due to the occurrence of colour polymorphism coupled with sex inversion, is discussed. The question of the probable systematic status of Spicara chryselis is raised, and in particular whether it should be regarded as a separate species or merely a colour form of one of the other two Mediterranean species (S. smaris and S. maena) belonging to this genus. The results of both electrophoretic studies of their eye‐lens proteins and morphological studies of these three forms are discussed, and the conclusion is drawn that S. chryselis is but a chromatic ecophenotype of the polymorphic species S. maena. The occurrence of such habitat‐associated colour polymorphism coupled with sex inversion is compared with a similar phenomenon previously observed in the labrid Corisjulis. The potential value of electrophoretic studies of eye lens proteins in the solution of such complicated intra‐ and inter‐specific systematic problems is emp