2022 Volume 70 Issue 1 Pages 55-64
Ocean acidification has troubled many ecologists during recent decades. Elevated CO2 levels have shown to have a significant impact on fish otolith formation; however, it is still unclear if the cause of these impacts is H+ or HCO3-, as this has not been studied yet. In this study, we used juvenile marbled flounder, Pseudopleuronectes yokohamae as a model organism, to examine the effects of acidification caused by H+, not elevated CO2, on fish otolith formation. The fish were reared under a control (pH 7.8) and two HNO3 treatments [pH 7.5 and pH 6.8]. The results of the principal component analysis showed a trend of larger otolith size (perimeters, areas, width, and length) under the pH 6.8 treatment than under the control and pH 7.5 treatments. The ANOVA results showed that there were significant shape differences (mainly in terms of solidity) between the HNO3 treatment groups and the control group. Our results indicate that H+ could be the main factor causing the oversized and smoother otoliths under ocean acidification conditions.