Fin-ray count variation in 0-group flatfish: Plaice (Pleuronectes platessa (L.)) and flounder (Platichthys flesus L.) on the west coast of Ireland

During the autumns of 2005 and 2006, 0-group plaice (Pleuronectes platessa (Linnaeus)) and flounder (Platichthys flesus Linnaeus) were collected from beaches in Galway and Kerry on the west coast of Ireland by beach seining and push netting. Characteristics used to identify adult flatfish were not discernible in these juveniles, and fin-ray counts were used to differentiate between the species. The dorsal, anal and caudal rays of 325 plaice and 116 flounder were counted and plotted, resulting in a clear separation between the two species. Thus, fin-ray counts may be used to reliably separate these two species on the west coast of Ireland. The ranges observed for both species lie within those previously reported. Analysis of fin-ray counts for both plaice and flounder showed no significant difference between the two regions studied. However, for plaice, a significant difference in dorsal fin-ray numbers was observed between the Galway beaches. No evidence of plaice/flounder hybrids, as identified by intermediate ray counts, was observed. There was no relationship between the numbers of dorsal and anal fin rays for plaice. However, a positive relationship was found between the numbers of dorsal and anal rays for flounder.