MEPS 192:287-294 (2000)  -  doi:10.3354/meps192287

ABSTRACT: We studied the circadian variations of the ionic composition ([Na⁺], [K⁺], [Cl^-]), total CO₂ ([tot CO₂]), and protein concentration ([protein]) in the plasma and endolymph in the distal and proximal sides of the sacculus in the turbot Psetta maxima. Daily variations in total plasma calcium ([tot Ca]) were also recorded. Significant diurnal fluctuations occurred in most parameters and the spatial heterogeneity of the endolymph composition was maintained throughout a 24 h period. The main parameters implicated in otolith calcification, endolymph [tot CO₂] and endolymph [protein], fluctuated diurnally. [tot CO₂] was highest and [protein] lowest at night; the relative concentrations were reversed during the day. The inverse, alternating relationship of maximal and minimal [tot CO₂] and [protein] implies that calcium carbonate and organic matrix rates of deposition vary in antiphase. We therefore propose that in the turbot P. maxima, in autumn, the incremental zone (L-zone) is formed at night whereas the discontinuous zone (D-zone) is formed during the daytime.

KEY WORDS: Daily cycle · Endolymph · Otolith · Chemical composition · Teleost