Abstract
The contents of total and diffusible calcium, and total magnesium in the otolith fluids of flatfish and rainbow trout were monthly determined in relation to the formation of the opaque and translucent zones in the otolith. From a comparative point of view, the sera obtained from these individuals were also analyzed for the three elements.
1. The concentration of total calcium in the otolith fluids of the two species examined is low as compared with that of the respective sera, and it is nearly equal to the level of diffusible calcium in the sera.
2. In the otolith fluid, however, diffusible calcium occupies about 72.7% of the total in flatfish and about 73.7% in rainbow trout. Moreover, in this fluid of flatfish, a seasonal change is found to occur in the diffusible calcium concentration, decreasing to 65.4% of the total in the period of the opaque zone formation of the otolith and increasing to 79.1% in the period of the translucent zone formation.
3. Total magnesium contained in the otolith fluid is found to be either roughly equal to that of the serum in rainbow trout or rather to be higher in flatfish, though no distinct seasonal change corresponding to the period of the zone formation of otolith is found in the fish used. Accordingly, the Ca/Mg ratio is lower in the otolith fluid of both species than in the respective sera.
