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Variability of squamation of European flounder Platichthys flesus (Pleuronectidae) in the White Sea

Squamation of the European flounder Platichthys flesus is formed by the common cycloid scales and the bony plates. The number of the bony plates and their localization on the body vary considerably in the flounders from different parts of their range. Study of the variability of bony plates coverage in the European flounder are of importance for understanding structural diversity and for use of this character for morphological differentiation of the local populations. We compared the bony plates on the eye side of the body in the flounders from Chupa Inlet (Kandalaksha Bay) and from the delta of the North Dvina River (Dvina Bay). The localization and the number of the bony plates near the bases of dorsal, anal, pectoral fins and above/below of the lateral line were analyzed. Our results clearly showed that the compared samples can be characterized by certain phenotypes, differing by number and location of the bony plates on the eye side of the fish body. The individuals of one phenotype were found in Chupa Inlet only. Small amount of the bony plates on the body and the presence of relatively wide aggregation of the bony plates near the pectoral fin are the traits of this phenotype. Three phenotypes were distinguished among fishes from the North Dvina delta. The absence of the bone plates on the most part of the body is typical for the prevalent phenotype. Individuals of the second phenotype were similar to the flounder from Chupa Inlet. Large amount of the bony plates covering the whole eye side of the body is characteristic for the third phenotype. The obtained results complement the existing data on the variability of squamation of the White Sea flounders, and indicate the importance of this character in the study of the differences between local populations in this region.