Mangrove Fishes Rely on Emersion Behavior and Physiological Tolerance to Persist in Sulfidic Environments.

Hydrogen sulfide (H2 S) is a potent respiratory toxin that makes sulfidic environments tolerable to only a few organisms. We report the presence of fishes (Kryptolebias marmoratus, Poecilia orri, Gambusia sp., and Dormitator maculatus) in Belizean mangrove pools with extremely high H2 S concentrations (up to 1,166 μM) that would be lethal for most fishes. Thus, we asked whether the three most prevalent species (Kryptolebias, Poecilia, and Gambusia) persist in sulfidic pools because they are exceptionally H2 S tolerant and/or because they can leave water (emerse) and completely avoid H2 S. We show that both physiological tolerance and emersion behavior are important. Kryptolebias demonstrated high H2 S tolerance, as they lost equilibrium significantly later than Poecilia and Gambusia during H2 S exposure ( 1,188 ± 21 μM H2 S). However, the fact that all species lost equilibrium at an ecologically relevant [H2 S] suggests that physiological tolerance may suffice at moderate H2 S concentrations but that another strategy is required to endure higher concentrations. In support of the avoidance behavior hypothesis, H2 S elicited an emersion response in all species. Kryptolebias was most sensitive to H2 S and emersed at H2 S concentrations 52% and 34% lower than Poecilia and Gambusia, respectively. Moreover, H2 S exposure caused Kryptolebias to emerse more frequently and spend more time out of water compared to control conditions. We suggest that physiological H2 S tolerance and emersion behavior are complementary strategies. The superior H2 S tolerance and amphibious capability of Kryptolebias may explain why this species was more prevalent in H2 S-rich environments than other local fishes.