Mudskippers gulp air and hold water in enlarged gill chambers, but a substantial share of their oxygen uptake while stranded on mud comes from gas exchange directly across their moist skin and the lining of the mouth and throat. This works only as long as the surface stays wet, which is why the fish periodically rolls in puddles or slaps its tail to keep its skin damp between tides.
Studies on related Periophthalmus species estimate that cutaneous and buccal respiration can supply a large fraction of resting oxygen demand in air, sometimes exceeding gill-based uptake when the fish is inactive on exposed mud. Exact percentages vary by species, temperature and activity level, and most detailed measurements come from a handful of closely related mudskipper species rather than exhaustive testing across the whole genus.
A common misconception is that mudskippers have lungs like amphibians. They do not; their lungs are absent, and air breathing instead relies on modified skin, mouth and gill-chamber tissue kept moist and vascularised. Researchers are still refining how these fish balance water loss against gas exchange across different mudflat microclimates and tidal regimes.