Pattern Identification in the Microstructure of Sockeye Salmon (Oncorhynchus nerka) Otoliths

Abstract

Otoliths of sockeye salmon (Oncorhynchus nerka) display daily rings in the microstructure when reared in temperatures above ~ 5 °C. Otolith formation ceases in fed fry held at or below 5 °C, although body growth continues at a much reduced rate. Foraging periodicity is not a significant factor in ring periodicity; rather, the existence of an entrained biological rhythm is supported. Subdaily rings are present on some otoliths, but they are faint and poorly defined. A noticeable and consistent ring corresponding to the date of first feeding is identified. The otolith diameter—body length relationship varies significantly between fed and starved experimental groups. The relation measured for starved groups is thought to be a short-term response to brief periods of starvation.Key words: otoliths, daily rings, sockeye salmon, environmental factors