EFFECTS OF EXHAUSTING EXERCISE ON ACID-BASE REGULATION IN SKIPJACK TUNA (KATSUWONUS PELAMIS) BLOOD' S. F. PERRY? C. DAXBOECK,' B. EMMETT? P. W. HOCHACHKA,4 AND R. W. BRILL Southwest Fisheries Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Honolulu, Hawaii 968 12 (Accepted 1/2/85) The effects of exhausting exercise on acid-base balance of skipjack tuna blood were investigated. Following exercise, tuna displayed a mixed respiratory/metabolic acidosis with blood pH being reduced by -0.4 units. The respiratory component (51% of the initial acidosis) was compensated following 20 min of recovery, while the blood metabolic acid load zyxwvut (H'm; -8 mM) was cleared after only 50 min. At that time, there was a great discrepancy between blood lactate load and H'm load because blood lactate levels were still increasing. The significance of these results is discussed with reference to the tuna's habitat, behavior, and physiology. INTRODUCTION Skipjack tuna zyxwvutsrq (Katsuwonus pelurnis) have a remarkable capacity to maintain high cruising speeds for long periods of time. The estimated maximum sustainable speed for this species is 6- IO body lengths/s (Yuen 1970; Dizon, Brill, and Yuen 1978). While the sustainable velocities greatly exceed those of most other fish examined, the maximum swimming speeds attainable by skipjack tuna (I 5-20 body lengths/s; Brill and Dizon [1979]) do not differ greatly from those of other active teleosts (e.& Salmo zyxwvutsrq gairdneri, I5 body lengths/s [Webb 1971; Mosse 1979; Johnston 19821). Similarly, the amount of time it zyxwvut ' This study was funded by National Marine Fish- eries Service, Pacific Gamefish Foundation, and an NSERC operating grant to P.W.H. The authors would like to thank Dr. C. M. Wood and Dr. D. J. Randall for providing some necessary equipment. As visitors to the Kewalo Research Facility, S.F.P., C.D., B.E., and P.W.H. wish to express thanks to the entire staff for their hospitality and support during this study. We are grateful to Dr. C. M. Wood, Dr. R. B. Boutilier, and Dr. P. J. Walsh for critically reading the manuscript. S.F.P. was supported by an E. B. Eastburn Postdoctoral Fellowship. * Present address: Department of Biology, Univer- sity of Ottawa, 30 Somerset E., Ottawa, Ontario, Canada KIN 6N5. ' Present address: Pacific Gamefish Foundation, P.O. Box 3189, Kailua-Kona, Hawaii 96740. ' Present address: Department of Zoology, Univer- sity of British Columbia, 6270 University Blvd., Vancouver, British Columbia, Canada V6T 2A9. Physiol. zyxwvutsrqpo 2001. zyxwvutsrqp 58(4):421-429. 1985. zyxwvutsrqponm 0 1985 zyxwvutsrqponmlkj by The University of Chicago. All rights reserved. 003 1-935X/85/5804-8486$02.a0 takes to reach exhaustion during burst activity also does not differ greatly from those of other active fish. However, there are reasons to believe that tuna may be better adapted for recovery from burst- swimming activity than are other teleosts: tuna exhibit relatively rapid lactate clear- ance (1-2 h; [Barrett and Connor 19641) compared to the 8-12 h or even longer period seen in other teleosts (e.g., 24 h for flounder [Wood, McMahon, and Mc- Donald 19771 and > 12 h for rainbow trout [Turner, Wood, and Clark 1983~1). Rapid acid-base recovery following burst swim- ming clearly would be advantageous to skipjack tuna, considering that they inhabit the open ocean (an environment that pro- vides little shelter) and that high swimming speeds are a skipjack tuna's most potent defense against predators. In the present study we have investigated blood acid-base changes in skipjack tuna blood following exhausting exercise. In these experiments we were interested in determining the respiratory and metabolic components of the acid-base disturbance following burst swimming and the method and time course of recovery. Particularly, our interest was in determining if protons and lactate formed in equimolar amounts by muscular anaerobic metabolism (Ho- chachka and Mommsen 1983) are cleared at the same rate or whether a discrepancy in proton/lactate loads develops, as has been observed in other fish species (Piiper et al. 1972; Turner et al. 1983~; Turner, Wood, and Hobe 1983b). 42 1