Compensatory behaviour in response to sulphide-induced hypoxia affects time budgets, feeding efficiency, and predation risk

Background: In habitats containing toxic hydrogen sulphide, fish breathe at the water’s surface to stay alive. This behaviour is called aquatic surface respiration. Questions: What effects does this compensatory behaviour have? Does it constrain individuals’ time budgets? Does it have a negative effect on foraging? Does it increase susceptibility to predators? Organisms and locations: Atlantic mollies (Poecilia mexicana: Poeciliidae, Teleostei) and sulphur mollies (P. sulphuraria) inhabiting sulphidic and non-sulphidic habitats in Tabasco (Mexico). Methods: We observed time budgets of fish in sulphidic and non-sulphidic habitats. We measured the amount of food eaten by fish in the various habitats. We exposed fish to a predator (giant water-bug, Belostoma sp.: Belostomatidae, Hemiptera) in mesocosms placed in sulphidic and non-sulphidic habitats. Results: There was an inverse correlation between time spent performing aquatic surface respiration and time dedicated to foraging. Furthermore, fish in non-sulphidic habitats had more food in their guts than conspecifics from sulphidic habitats. Our predation experiments showed no overall difference in capture rates between sulphidic and non-sulphidic sites; however, males were disproportionately preyed upon.