Coward or braveheart: extreme habitat fidelity through hypoxia tolerance in a coral-dwelling goby.

Coral reef fishes are not known for their hypoxia tolerance. The coral-dwelling goby, Gobiodon histrio, rarely leaves the shelter of its host coral colony. However, our measurements indicate that this habitat could become hypoxic on calm nights ([O(2)] minima=2-30% of air saturation) due to respiration by the coral and associated organisms. Moreover, at very low tides, the whole coral colony can be completely air exposed. Using closed respirometry in water, we found that G. histrio maintains O(2) uptake down to 18% of air saturation, and that it can tolerate at least 2 h at even lower O(2) levels. Furthermore, during air exposure, which was tolerated for more than 3 h, it upheld a rate of O(2) consumption that was 60% of that in water. The hypoxia tolerance and air breathing abilities enables this fish to stay in the safety of its coral home even when exposed to severe hypoxia or air. To our knowledge, this is the first report of hypoxia tolerance in a teleost fish intimately associated with coral reefs.