HIGH-ENERGY TURNOVER AT LOW-TEMPERATURES - RECOVERY FROM EXHAUSTIVE EXERCISE IN ANTARCTIC AND TEMPERATE EELPOUTS

Earlier work on Notothenioids led to the hypothesis that a reduced gly colytic capacity is a general adaptation to low temperatures in Antarc tic fish. In our study this hypothesis was reinvestigated by comparing changes in the metabolic status of the white musculature in two relat ed zoarcid species, the stenothermal Antarctic eelpout Pachycara brach ycephalum and the eurythermal Zoarces viviparus during exercise and su bsequent recovery at 0 degrees C. In both species, strenuous exercise caused a similar increase in white muscle lactate, a drop in intracell ular pH (pH(i)) by about 0.5 pH units, and a 90% depletion of phosphoc reatine. This is the first study on Antarctic fish that shows an incre ase in white muscle lactate concentrations. Thus the hypothesis that a reduced importance of the glycolytic pathway is characteristic for co ld-adapted polar fish cannot hold. The recovery process, especially th e clearance of white muscle lactate, is significantly faster in the An tarctic than in temperate eelpout. Based on metabolite data, we calcul ated that during the first hour of recovery aerobic metabolism is incr eased 6.6-fold compared with resting rates in P. brachycephalum vs. an only 2.9-fold increase in Z. viviparus. This strong stimulation of ae robic metabolism despite low temperatures may be caused by a pronounce d increase of free ADP levels, in the context of higher levels of pHi and ATP, which is observed in the Antarctic species. Although basal me tabolic rates are identical in both species, the comparison of metabol ic rates during situations of high-energy turnover reveals that the st enothermal P. brachycephalum shows a higher degree of metabolic cold c ompensation than the eurythermal Z. viviparus. Muscular fatigue after escape swimming may be caused by a drop of the free energy change of A TP hydrolysis, which is shown to fall below critical levels for cellul ar ATPases in exhausted animals of both species.