THE RELATION BETWEEN EXERCISE AND 

 BIOCHEMICAL CHANGES IN RED AND WHITE MUSCLE AND 

 LIVER IN THE JACK MACKEREL, Trachnrus symmetricns 



Austin W. Pritchard," John R. HuNTERr and Reuben Lasker'' 



ABSTRACT 



Glycogen, lactic acid, and fat concentration in red and white muscle and glycogen in the liver of jack 

 mackerel, Trachurus symmetricns, were measured after periods of forced swimming by Trachurus at 

 speeds above, below, and at the sustained speed threshold. Failure to swim at any speed was associ- 

 ated with an almost complete depletion of glycogen in the white muscle only. The trend of glycogen 

 use in the red muscle closely followed that of the liver and was not correlated with failure to swim. 

 Reduction of glycogen levels in red muscle and liver were associated with extended periods of swim- 

 Lipid use was slow and not correlated with fatigured muscle and was insignificant in white muscle, 

 ming. High lipid content was characteristic of e. A decline in lipid concentration after exercise 

 occurred only in the red muscle and only after a swimming period of 6 hr at a subthreshold speed. 

 High lactate levels were characteristic of both muscle types and did not appear to be related to fatigue 

 at any swimming speed. 



The high lactate levels in white muscle, the almost complete depletion of glycogen in the white mus- 

 cle of exhausted fish, and the parallel pattern of glycogen depletion in red muscle and liver suggested 

 that white muscle was the primary locomotor organ near and above the threshold for sustained speed. 

 At these speeds red muscle like the liver may provide nutrients to the white muscle, provided time 

 for mobilization is sufficient. At speeds below the sustained speed threshold our analysis indicated 

 that both the red and white muscle systems were used but the relative significance of the locomotory 

 role played by each system could not be evaluated. 



The lateral musculature of many fishes may be 

 readily segregated by color into red and white 

 portions. Typically in active fishes the red 

 muscle makes up from 10 to 20^^ of the total 

 musculature and is arranged in a thin lateral 

 sheet just beneath the skin whereas the white 

 muscle makes up the underlying mass of the 

 myotome. The two muscle types also differ in 

 the diameter of their muscle fibers, speed of 

 contraction, blood supply, mitochondrial content, 

 patterns of innervation, and glycogen and fat 

 content (Bone, 1966). 



The accepted view of the function of red 

 and white muscle tissues in fishes was outlined 

 by Bone (1966). He concluded from his own 

 work on dogfish and from an extensive liter- 

 ature review that the two muscle fibers repre- 

 sent two separate motor systems which operate 



^ Zoology Department, Oregon State University, Cor- 

 vallis, Oreg. 97331. 



' National Marine Fisheries Service Fishery-Ocean- 

 ography Center, La Jolla, Calif. 92037. 



Manuscript received January 1971. 



FISHERY BULLETIN: VOL. 69, NO. 2, 1971. 



independently, utilize different metabolites, and 

 serve different locomotory functions, viz., the 

 red muscle is used for slow cruising speeds and 

 functions by aerobic metabolism of fat whereas 

 the white muscle is used for rapid bursts of 

 swimming and is driven by anaerobic glycolysis. 

 Bone's conclusions have subsequently been sup- 

 ported by measurements of oxygen uptake in 

 red and white muscle by Gordon (1968) and by 

 electrophysiological studies on oceanic skipjack, 

 Katsiuvonus pelamis, by Rayner and Keenan 

 (1967). On the other hand, Braekkan (1956) 

 and Wittenberger (1967) believe the red muscle 

 has no independent locomotor role and functions 

 as a metabolic organ for the white muscle. Elec- 

 trode recordings from the red muscle (Bone, 

 1966; Rayner and Keenan, 1967) have provided 

 irrefutable evidence for an independent loco- 

 motor function of red muscle at certain slow 

 speeds, but the metabolic independence of the 

 two muscle systems and their metabolic and 

 locomotor function at higher speeds is still open 



379 



