Reverse translation: effects of acclimation temperature and acute temperature challenges on oxygen consumption, diffusive water flux, net sodium loss rates, Q(10) values and mass scaling coefficients in the rainbow trout (Oncorhynchus mykiss)

摘要

Our understanding is limited on how fish adjust the effective permeability of their branchial epithelium to ions and water while altering O-2 uptake rate (MO2) with acute and chronic changes in temperature. We investigated the effects of acclimation temperature (8 degrees C, 13 degrees C and 18 degrees C) and acute temperature challenges [acute rise (acclimated at 8 degrees C, measured at 13 degrees C and 18 degrees C), acute drop (acclimated at 18 degrees C, measured at 8 degrees C and 13 degrees C) and intermediate (acclimated at 13 degrees C, measured at 8 degrees C and 18 degrees C)] on routine MO2, diffusive water flux, and net sodium loss rates in 24-h fasted rainbow trout (Oncorhynchus mykiss). In the temperature challenge tests, measurements were made during the first hour. In acclimated trout at all temperatures, allometric mass scaling coefficients were much higher for diffusive water flux than for MO2. Furthermore, the diffusive water flux rate was more responsive (overall Q(10) = 2.75) compared to MO2 (Q(10) = 1.80) over the 8-18 degrees C range, and for both, Q(10) values were greater at 8-13 degrees C than at 13-18 degrees C. The net Na+ flux rates were highly sensitive to acclimation temperature with an overall Q(10) of 3.01 for 8-18 degrees C. In contrast, very different patterns occurred in trout subjected to acute temperature challenges. The net Na+ flux rate was temperature-insensitive with a Q(10) around 1.0. Both MO2 and diffusive water flux rates exhibited lower Q(10) values than for the acclimated rates in response to either acute increases or decreases in temperature. These results fit Pattern 5 of Precht (undercompensation, reverse effect) and more precisely Pattern IIB of Prosser (reverse translation). These inverse compensatory patterns suggest that trout do not alter their rates very much when undergoing acute thermal challenges (diurnal fluctuations, migration through the thermocline). The greater changes seen with acclimation may be adaptive to long-term seasonal changes in temperature. We discuss the roles of aquaporins, spontaneous activity, and recent feeding in these responses.