Abstract
The measurement of oxygen dissociation curves of hemoglobins of cultured yellowtail Seriola quinqueradiata, red sea bream Chrysophrys major, and black sea bream Mylio macrocephalus revealed that yellowtail hemoglobin has a unique property in oxygen equilibria. It showed a large Bohr effect, Δlog P50/ΔpH=-1.3, between pH 7.4 and 6.7 but lacked the pH dependence almost entirely below pH 6.7 in contrast to the hemoglobins of the two breams. The sonicate of the red tide plankton, Chattonella sp. which causes the mass mortality of cultured yellowtail, had little influence on the oxygen dissociation curves of yellowtail hemoglobin. However, the pH values of the gills and blood of the yellowtails kept in the red tide water fell down to 6.7.
From these results and previous findings of other workers, it may be said that some irritating substance from the red tide plankton should trigger a violent swim of the fish, which inevitably induces the accumulation of lactic acid in the muscle and the drop of pH in the blood, leading the fish to asphyxiation even in the oxygen saturated sea water.
