O efeito da concentração de oxigênio na tolerância térmica em duas espécies de peixes de respiração bimodal: mudanças fisiológicas e comportamentais

Abstract

The ability to tolerate adverse conditions determines how vulnerable the species will be to environmental changes. Several studies demonstrate a reduction in the heat tolerance levels of aquatic breathing fish species when exposed to hypoxia. However, there is no information about the effect of hypoxia on thermal tolerance in bimodal breathing fish species. Several groups of Amazonian fish can breathe air in a facultative way, among them the loricariids that use the stomach adapted to breathe air. In the family Loricariidae there are stomachs with different morphological configurations, which may determine the ability of the species to maximize the oxygen uptake from the air and possibly extend its thermal limits, as discussed by the theory of oxygen-limited thermal tolerance capacity (OCLTT). Therefore, we aimed to evaluate the effect of hypoxia on the thermal limits and the physiological and behavioral mechanisms of two facultative air breathers, Pterygoplichthys pardalis and Ancistrus dolichopterus. Pterygoplichthys pardalis has a larger, more irrigated stomach with maximized capacity to capture oxygen from the air, contrasting with the morphology found in A. dolichopterus, which has a less efficient stomach for oxygen uptake. For P. pardalis, the thermal tolerance limits are independent of oxygen concentration. However, by limiting access to the surface, we found a decrease in CTmax under hypoxic conditions. On the other hand, in A. dolichopterus CTmax is limited by oxygen concentration from concentrations below the Pcrit when surface access is available and does not differ between animals with and without access to air. Therefore, our results demonstrate that air breathing increases heat tolerance capacity in species that can maximize oxygen uptake from air. Thus, such species have a greater adaptive advantage when compared with aquatic breathing species or species with less efficiency in oxygen uptake.