The "oxygen capacity-dependent thermal tolerance" (OCLTT) hypothesis suggests that the ability of ectotherms to tolerate heat is limited by their ability to supply oxygen to their tissues at various temperatures set by the capacity of the cardiovascular and respiratory systems. Optimal temperatures and oxygen can supply enough energy through adenosine triphosphate (ATP) via the electron transport chain to support fitness-related processes. Conversely, stressful temperatures indicate an energetic limitation that could describe physiological parameters and biogeographical patterns. Our study aimed to determine if stressful temperatures could be related to immunological performance under a macroecological approach. To prove this hypothesis, we recapitulated key immune parameters, including total hemocyte count, hemagglutination, phenoloxidase system, and lysozyme activity, of wild mayan octopus (