Hydrogen sulphide sensitivity and tolerance in genetically distinct lineages of a selfing mangrove fish (Kryptolebias marmoratus)

Mangroves are critical marine habitats. High hydrogen sulphide (H₂S) is a feature of these important ecosystems and its toxicity creates a challenge for mangrove inhabitants. The mangrove rivulus (Kryptolebias marmoratus) is a selfing, hermaphroditic, amphibious fish that can survive exposure to 1116 μM H₂S in the wild. These fish rely on cutaneous respiration for gas and ion exchange when emerged. We hypothesized that the skin surface is fundamentally important in H₂S tolerance in these mangrove fish by limiting H₂S permeability. To test our hypothesis, we first disrupted the skin surface in one isogenic lineage and measured H₂S tolerance and sensitivity. We increased water H₂S concentration until emersion as a measure of the ability to sense and react to H₂S, which we refer to as sensitivity. We then determined H₂S tolerance by preventing emersion and increasing H₂S until loss of equilibrium (LOE). The H₂S concentration at emersion and LOE were significantly affected by disrupting the skin surface, providing support that the skin is involved in limiting H₂S permeability. Capitalizing on their unique reproductive strategy, we used three distinct isogenic lineages to test the hypothesis that there would be genetic differences in H₂S sensitivity and tolerance. We found significant differences in emersion concentration only among lineages, suggesting a genetic component to H₂S sensitivity but not tolerance. Our study also demonstrated that external skin modifications and avoidance behaviours are two distinct strategies used to tolerate ecologically relevant H₂S concentrations and likely facilitate survival in challenging mangrove habitats.