Fig. 1. Three-dimensional drawing of a Periophthalmus modestus burrow showing monitoring device positions: O₂ electrode (O), endoscope camera (E), tube for gas injection (G), stainless-steel electrodes (S) for impedance measurement (I), and pressure transducer tube connection (T). Thick dotted line above egg chamber shows the level of burrow excavation required for instrumentation. Thin broken line under the egg chamber shows approximate position of the air–water interface.