exp. Biol. 147, 493-505 (1989) 493 rinted in Great Britain © The Company of Biologists Limited 1989 THE SCALING OF AEROBIC AND ANAEROBIC MUSCLE POWER IN RAINBOW TROUT (SALMO GAIRDNERI) BY EDWARD M. GOOLISH University of Michigan, School of Natural Resources, Ann Arbor, MI 48109, USA and Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, England, NR33 OHT Accepted 23 June 1989 Summary The scaling of anaerobic metabolism and red muscle mass was examined in rainbow trout (Salmo gairdneri) ranging in size from 2 to 1200 g. The initial rate of white muscle lactate production during maximal burst activity was significantly higher in large (28-1 cm) than in small (8-0 cm) fish. 'Resting' lactate concen- trations in anesthetized trout (approximately 30 s of stress) increased with fish size, also reflecting higher glycolytic potential for larger fish. Maximum muscle lactate concentrations following 6min of exhaustive exercise increased from approxi- mately 25 to 45 ; umolg~ 1 with increased fish size (= L 0 ' 36 , where L is fish length). Total white muscle lactate production, including changes in muscle mass, scaled as L 3 ' 52 . A scaling comparison of total anaerobic capacity with theoretically predicted power requirements indicated decreased burst swimming performance with increased size. Red muscle mass increased from approximately 1 to 3 % of body mass with increased fish size. The positive allometry in red muscle mass (= L 3 62 ) is greater than the scaling of power requirements during aerobic swimming predicted from hydrodynamic theory, and may provide compensation for decreased mass-specific power output with increased size. Introduction A fundamental issue in the study of vertebrate swimming is the relationship between muscle power production and the power required to achieve a particular level of performance (Gray, 1936; Bainbridge, 1961; Webb, 1978). The scaling of power requirements has been the subject of considerable analysis (Vlymen, 1974; Weihs, 1977; Webb etal. 1984) and, in general, displays positive allometry for both sustained and burst swimming. Less attention has been given to the scaling of muscle power output, but it appears that the mechanical limitations for maximum power during a single muscle contraction are not size-dependent (Schmidt- Nielsen, 1977; Webb & Johnsrude, 1988). The scaling of muscle power output in fish is complicated by its differentiation into aerobic red muscle tissue (used for sustained swimming) and anaerobic white Key words: lactate, red muscle tissue, swimming, anaerobic capacity, fish.