Konishi et al.[1969] demonstrated the occurrence of
CO2receptors in the palatine surface of carp. The receptors
are sensitive also to acids, but the sensitivity was highest for
CO2under the same pH conditions. Gill ventilatory movement was suppressed by stimulation of these CO2receptors.
Similar CO2receptors were demonstrated for Japanese eel,
Anguilla japonica[Yoshii et al., 1980] and rainbow trout
[Yamashita et al., 1989]: Thresholds of these CO2receptors
are 0.5 torr and 0.6 torr, as calculated from the reported
dissolved CO2concentrations (210
5
mol L
1
and 4
10
5
mol L
1
) for the eel and trout, respectively. In
addition, fish have branchial CO2 receptors that seem to
be involved in cardiac and ventilatory responses to changes
in water CO2levels [Perry and Gilmour, 2002]