Morphological characterisation of salmon [Salmo salar L., 1758] aged 0plus, 1plus and 2plus, stocked in Pomeranian rivers

Characterisation of salmon (Salmo salar) aged 0+, 1+, 2+, stocked in Pomeranian rivers, involved 25 plastic and 13 meristic characters, the opercular bone arrangement, and coloration. Coloration of body and fins, appearing at the age of 0+ at the fork length of 6-10 cm belonged to the earliest species-specific traits. Typical values of certain species-specific characters, such as tail base width, caudal fin incision (as per cent of l. caudalis), and the length of the upper jaw (as per cent of l. capitis) were recorded as early as in the fish aged 0+. Other characters, such as the opercular bone arrangement, were observed in those individuals aged 1+ and only in some fish aged 0+. The typical salmon anal fin shape occurred in some of the salmon aged 1+ and 2+ only. The study showed a high variability and significant differences in meristic and plastic characters between individuals grown in various rivers.