Effects of acidity and a metabolic inhibitor on incorporation of calcium and inorganic carbon into endolymph and otoliths in salmon Oncorhynchus masou

ABSTRACT:   To investigate the mechanisms of calcium carbonate formation of teleost otoliths, using the double labeling technique of ⁴⁵Ca²⁺ and H¹⁴CO₃^–, the effects of tissue elimination, a metabolic inhibitor (cyanide) and acidity on the incorporation of calcium and inorganic carbon into endolymph and otoliths were examined. Incorporation of calcium and inorganic carbon into otoliths was decreased to 36% and 45%, respectively, by removing the sacculus. In contrast, cyanide inhibited incorporation of inorganic carbon and calcium into endolymph and otoliths in a concentration-dependent manner. Acidity in the incubation medium decreased the accumulation of inorganic carbon within the endolymph and otoliths. Calcium incorporation was not affected by variation of pH in the medium. These results indicate that calcium and bicarbonate are actively transported to endolymph via the sacculus, and it is suggested that the transport is involved in the oversaturation state for calcium carbonate in the endolymph and regulates subsequent calcification of otoliths.