Fig. 4. The overall net acid or base flux to the water from fed and unfed fish. Positive values indicate a net base flux (J_netOH^–; µmol kg^–1 h^–1), whereas negative values indicate a net acid flux (J_netH⁺; µmol kg^–1 h^–1). Open symbols indicate unfed fish, filled symbols indicate fish that were fed immediately before the experiment began. Data were calculated from the difference between values shown in Fig. 2 and Fig. 3 on an individual fish basis (see Materials and methods for further explanation). Values are means ± s.e.m.; N=6 for each treatment. Significant difference (P<0.05) between fed and unfed fish.