Otolith calcification in Atlantic salmon parr, Salmo salar L. and its relation to photoperiod and calcium metabolism

Abstract
Otolith calcification in Atlantic salmon parr, Salmo salar, was investigated using a radioisotope of calcium, 45Ca. Otolith calcification was found to be entrained to light‐dark cycles in salmon parr, calcium accumulation on to otoliths declining at night and resuming at dawn. The decline in Otolith calcification at night coincided with a diel decline in plasma calcium concentration. The influence of extracellular calcium on otolith increment formation was considered by inducing hypocalcemia. Induced hypocalcemia resulted in a short‐term net loss of calcium from the otolith. The results are discussed in relation to previous studies of the role of extracellular calcium in otolith formation.