TIME-COURSE OF RESPIRATORY METABOLIC ADJUSTMENTS OF A SOUTH-AMERICAN FISH, PROCHILODUS-SCROFA, EXPOSED TO LOW AND HIGH-TEMPERATURES

The time-course for the thermal acclimation of aerobic metabolism was determined for juvenile and adult P. scrofa by following the modificat ions in oxygen consumption (O-.(2)). Fish previously acclimated at 15 and 25 degrees C and transferred to water temperature 10 degrees C and above, showed 3-4-fold increase in O-.(2) in the first 6 h after the change in temperature, reaching a stable O-.(2) level in 24 and 48 h ( adult and juvenile fish, respectively). Fish acclimated at 35 and 25 d egrees C and transferred to water temperature 10 degrees C below that to which they were previously acclimated decreased the O-.(2) in the f irst 6 h after the change in water temperature (3.0-fold lower, from 3 5 to 25 degrees C for both fish sizes and 6.5- and 3.0-fold lower from 25 to 15 degrees C for juvenile and adult fish, respectively), reachi ng a stable O-.(2) level in 48 h (from 25 to 15 degrees C) and 24-72 h (from 35 to 25 degrees C). Regardless of the direction of water tempe rature change, P. scrofa showed partial O-.(2) compensation and short time-course for the adjustments in aerobic metabolism, reaching a stab le rate at the new water temperature in 1-3 days. These results indica te an ecological advantage for this species, mainly for the adult fish , which migrate along rivers prior to reproduction and which may exper ience fluctuations in water temperature, including the heated effluent s from electrical power stations.