Responses of skilletfish Gobiesox strumosus to high temperature and low oxygen stress.

This study quantified physiological responses of skilletfish Gobiesox strumosus exposed to thermal and oxic stress. Fish acclimated at 12, 22 and 32 degrees C had low oxygen tolerance values (mean +/-s.d.) of 0.40 +/- 0.09, 0.40 +/- 0.08 and 0.35 +/- 0.03, and critical thermal maxima (mean +/-s.d.) of 33.2 +/- 0.5, 38.1 +/- 0.0 and 39.5 +/- 0.3 degrees C, respectively. Furthermore, G. strumosus were oxygen conformers at all acclimation temperatures, i.e. the fish allowed oxygen consumption rates to decrease with ambient oxygen concentration. High temperature tolerance, low oxygen tolerance and decreasing metabolic rates during hypoxic events allow the fish to survive harsh environmental conditions encountered in their natural environment.

Elevated pCO2 and Hypoxia Alter the Acid-Base Homeostasis of Developing Sheepshead Minnows, Cyprinodon variegatus.

Low dissolved oxygen and increased acidification are two environmental variables that concomitantly change in an estuarine environment, both of which are exacerbated by nutrient pollution and subsequent eutrophication. To better understand how estuarine residents compensate for daily fluctuations in these environmental variables, the interactive effects of acidification and hypoxia were assessed in developing sheepshead minnows (Cyprinodon variegatus) using a 2 by 2 factorial design over a 42-day exposure. Embryos were exposed to either acidic (partial pressure of CO2, pCO2, ~2000 µatm), hypoxic (reduced dissolved oxygen, ~2 mg l-1), or combined acidic and hypoxic conditions and monitored for development, hatch rate, and survival. Changes in oxygen consumption, anaerobic metabolism, oxidative stress, and acid-base balance were evaluated at three life stages (embryo, larval, and juvenile fish) to discern if and how fish compensate for these stressors during development. The combination of acidification and hypoxia delayed hatching in embryos and significantly decreased oxygen consumption (p<0.001) in all three life-stages. Neither acidification, hypoxia, nor the combination of the stressors impacted the anaerobic metabolism or oxidative stress of juvenile fish, but acid-base equilibrium was disrupted by all three treatments in larval fish. Elevated carbonic anhydrase activity was observed in the multi-stress treatment in embryos and larval fish, but not in juvenile fish. These results show that developing sheepshead minnows can re-establish cellular homeostasis in compensating to acidified and hypoxic waters.