Increased precision of growth data gained by reading multiple scales from each individual of Atlantic salmon (Salmo salar)

The precision of growth estimates based on fish scales often remains uncertain because of withinindividual variation in scale size and scale patterns, and also due to measurement errors. Based on scale readings of Atlantic salmon, we show that errors decreased with number of times and number of scales read per fish. The annual number of scale circuli was not constant, but positively correlated with annual specific growth rates. Number of circuli deposited after the last winter correlated positively with sampling date. There was no significant relationship between mean inter-circuli distance and the total circuli number during the first and second year at sea. For growth estimation in scientific studies, we recommend the use of 4-5 scales per fish. Consideration should be given to both circuli number and inter-circuli distances when estimating growth rate instead of relying on inter-circuli distances only. circuli number, inter-circuli distances, measurement error, sampling error, scale reading