Because larval zebrafish exhibit marked CO2 chemosensitivity by 4 days post fertilization (S. Miller and S.F. Perry; unpublished data; see also Fig. 1), it may be possible to elucidate the specific involvement of some of the K+ channel subtypes using selective gene knockdown approaches. It is likely that multiple types of K+ channels are involved, some of which respond to changes in extracellular pH and others which are modulated by intracellular pH.