Abstract

Air-breathing and non air-breathing gobiids inhabiting mangal tidepools on Pulau Hoga, Sulawesi, Indonesia, displayed differing types and degrees of behavioral and physiological adaptations to mitigate daily thermal and oxic stress. Non air-breathing Dusky Frillfin Goby, Bathygobius fuscus, and an undescribed sandflat goby species, Bathygobius sp., had higher critical thermal maxima, CTMax, (41.2 and 41.6 C, respectively) and lower critical thermal minima, CTMin, (11.0 and 11.4 C, respectively) than amphibious Common Mudskipper, Periopthalmus kalolo (40.8 and 12.8 C, respectively). During hypoxia, Common Mudskipper CTMax decreased significantly (38.8 C) and fish displayed a pronounced escape response, while Dusky Frillfin Goby showed no significant CTMax decrease (40.8 C). Neither bathygobiid attempted to escape during CTM trials. Common Mudskipper, however, attempted escape at temperatures significantly lower than their normoxic and hypoxic CTMax (36.4 and 35.0 C, respectively), and at temperatures higher than their normoxic CTMin (18.7 C). Temperature quotients (ratio of metabolic rates or oxygen consumption at two temperatures) for all species approached unity and ranged from 1.00 to 1.37 when exposed to a temperature increase of 6 C. Oxygen insensitive CTMaxima and a wide thermal scope allow bathygobiids to remain in tidepools during the most extreme conditions. In contrast, amphibious Common Mudskipper use a well developed behavioral escape response to avoid unfavorable environments. A sharply reduced temperature quotient response for these gobies diminishes the metabolic costs typically associated with diel temperature increases.