Elevated pCO2 and hypoxia alter the acid-base regulation of developing sheepshead minnows Cyprinodon variegatus

Lowered dissolved oxygen and pH levels are 2 environmental variables that concomitantly change in an estuarine environment and both 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 elevated partial pressure of CO2 (pCO(2)) and hypoxia were assessed in developing sheepshead minnows Cyprinodon variegatus using a 2 by 2 factorial design over a 42 d exposure. Embryos were exposed to either acidic (pCO(2): similar to 2000 mu atm), hypoxic (reduced dissolved oxygen, similar to 2 mg l(-)(1)), or combined acidic and hypoxic conditions and monitored for development, hatch rate, and survival. Measurements of anaerobic pathway use, oxidative stress, and acid-base regulatory enzymes were evaluated at 3 life stages (embryo, larva, and juvenile) to discern if and how fish compensate for these stressors during development. The combination of elevated pCO(2) and hypoxia delayed hatching in embryos but did not impact survival. Neither elevated pCO(2), hypoxia, nor the combination of the stressors elicited an increase in anaerobic metabolic pathways or impacted oxidative stress of juvenile fish. Measurements of enzymes related to acid-base regulation were elevated in all 3 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 compensate for acidified and hypoxic waters.