Comparison of the lethal effect of CO 2 and acidification on red sea bream ( Pagrus major) during the early developmental stages

Abstract

To compare the acute toxicity of CO 2- and HCl-acidified seawater, eggs and larvae of a marine fish, Pagrus major, were exposed to seawater equilibrated with CO 2-enriched gas mixtures (CO 2=5% or 10%, O 2=20.95% balanced with N 2) or seawater acidified with 1 N HCl at two pH levels (pH 6.2 (=5% CO 2) and 5.9 (=10% CO 2)) for 6 h (eggs) or 24 h (larvae). Mortalities of eggs were 85.8% (CO 2) and 3.6% (HCl) at pH 6.2, and 97.4% (CO 2) and 0.9% (HCl) at pH 5.9, while those of larvae were 61.2% (CO 2) and 1.6% (HCl) at pH 6.2, and 100% (CO 2) and 5.0% (HCl) at pH 5.9. Thus, previous research on the effects of acidified seawater on marine organisms, as a substitute for CO 2, has largely underestimated the toxic effects of CO 2.