Daily variations of the saccular endolymph and plasma compositions in the turbot Psetta maxima:relationship with the diurnal rhythm in otolith formation

Abstract

We studied the circadian variations of the ionic composition ([Na']. [K'], [Cl-]), total CO2 ([tot CO*]), and proteln 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 spati.al heterogeneity of the endolymph composition was maintained throughout a 24 h period. The main parameters implicated in otolith calcification, endolymph [tot CO,] and endolymph [protein], fluctuated diurnally. [tot CO,] 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]