Otolith mass asymmetries in the utricle and saccule of flatfish

The otolith mass of the saccules and utricles of plaice, Pleuronectes platessa (n = 39) and turbot, Psetta maxima (n = 21) was measured using an electronic microbalance. In the right-eyed plaice, the left utricular otoliths were found to be significantly heavier than the right (p < 0.0001), whereas no significant difference was found between left and right saccular otoliths (p < 0.751). In the left-eyed turbot, both the right utricular and saccular otoliths were found to be significantly heavier (in both cases, p < 0.0001). While the gene and regulative protein responsible for the peripheral biomineralisation process have been identified, it remains unclear how the symmetry between the right and left otoliths in fish species is regulated. Here it is likely that an additional central mechanism is involved. It must be assumed that similar processes govern the systematic asymmetry observed in flatfish such as the plaice and turbot. Taken together these findings are strongly suggestive of concomitant CNS modification and metamorphic plasticity, presumably represented in genetic code.