Osmo-respiratory compromise in the mosshead sculpin ( Clinocottus globiceps ): effects of temperature, hypoxia, and re-oxygenation on rates of diffusive water flux and oxygen uptake

In nature, mosshead sculpins ( Clinocottus globiceps ) are challenged by fluctuations in temperature and oxygen levels in their environment. However, it is unclear how mosshead sculpins modulate the permeability of their branchial epithelia to water and O 2 in response to temperature or hypoxia stress. Acute decrease in temperature from 13 to 6 o C reduced diffusive water flux rate by 22% and ṀO 2 by 51%, whereas acute increase in temperature from 13 to 25 o C increased diffusive water flux rate by 217% and ṀO 2 by 140%, yielding overall Q 10 values of 2.08 and 2.47 respectively. Acute reductions in oxygen tension from >95% to 20% or 10% air saturation did not impact diffusive water flux rates, however, ṀO 2 was reduced significantly by 36% and 65% respectively. During 1-h or 3-h recovery periods diffusive water flux rates were depressed while ṀO 2 exhibited overshoots beyond the normoxic control level. Many responses differed from those seen in our parallel earlier study on the tidepool sculpin, a cottid with similar hypoxia tolerance but much smaller gill area that occupies a similar environment. Overall, our data suggest that during temperature stress, diffusive water flux rates and ṀO 2 follow the traditional osmo-respiratory compromise pattern, but during hypoxia and re-oxygenation stress, diffusive water flux rates are decoupled from ṀO 2 .