Hydrogen sulphide toxicity and the importance of amphibious behaviour in a mangrove fish inhabiting sulphide-rich habitats

Abstract

We investigated amphibious behaviour, hydrogen sulphide (H 2 S) tolerance, and the mechanism of H 2 S toxicity in the amphibious mangrove rivulus (Kryptolebias marmoratus). We found that fish emersed (left water) in response to acutely elevated [H 2 S] (~ 130–200 µmol l −1 ). The emersion response to H 2 S may be influenced by prior acclimation history due to acclimation-induced alterations in gill morphology and/or the density and size of neuroepithelial cells (NECs) on the gills and skin. Thus, we acclimated fish to water (control), H 2 S-rich water, or air and tested the hypotheses that acclimation history influences H 2 S sensitivity due to acclimation-induced changes in (i) gill surface area and/or (ii) NEC density and/or size. Air-acclimated fish emersed at significantly lower [H 2 S] relative to fish acclimated to control or H 2 S-rich water, but exhibited no change in gill surface area or in NEC density or size in the gills or skin. Despite possessing exceptional H 2 S tolerance, all fish lost equilibrium when unable to emerse from environments containing extremely elevated [H 2 S] (2272 ± 46 µmol l −1 ). Consequently, we tested the hypothesis that impaired blood oxygen transport (i.e., sulphemoglobin formation) causes H 2 S toxicity in amphibious fishes. In vitro exposure of red blood cells to physiologically relevant [H 2 S] did not cause a substantial increase in sulphemoglobin formation. We found evidence, however, for an alternative hypothesis that H 2 S toxicity is caused by impaired oxidative phosphorylation (i.e., cytochrome c oxidase inhibition). Collectively, our results show that amphibious behaviour is critical for the survival of K. marmoratus in H 2 S-rich environments as fish experience impaired oxidative phosphorylation when unable to emerse.