Recruitment and maximal diameter of axial muscle fibres in teleosts and their relationship to somatic growth and ultimate size

Growth of white axial muscle fibres of ten species of freshwater teleosts from five families (Cyprinidae, Centrarchidae, Percidae, Salmonidae, Esocidae) possessing widely different growth rates and ultimate sizes have been studied. The dynamics of muscle increase (i.e. increase in fibre numbers and/or diameter) appears to determine the ability for rapid somatic growth and large ultimate size in teleosts. Thus, the largest and fastest growing species (smallmouth bass, lake whitefish, rainbow trout, muskellunge) show evidence of sustained recruitment of muscle fibres to a large size, in contrast to the smaller and slower growing species (bluntnose minnow, longnose dace). Pumpkinseed, bluegill and yellow perch are all intermediate in fibre growth dynamics, growth and ultimate size between the smaller and larger species. Moreover, the ability of teleosts to grow rapidly and attain a large ultimate size is dependent on the body length at which recruitment of new muscle fibres into the growing axial muscle ceases. The regression equation, y =– 0.29 + 2.26 ( x ), showing the relationship (r = 0.95) between ultimate body length, x , and fork length at cessation of recruitment, y , indicated that for these teleosts, recruitment tends to cease when the fork length reaches about 44% of the ultimate body length. Possible mechanisms to account for this relationship are proposed, and the role of the ultimate fibre diameter in posing limits to the ultimate size of the species is discussed.