Because skeletal muscle is the main contributor to body weight in most fish, it is probable that the size of a fish is limited by the growth of this tissue. Several aspects of both somatic size and skeletal muscle growth were investigated in white seabass (Atractoscion nobilis). One hundred and four subjects ranging in size from 1.3-91.8 cm standard length were examined to discern growth patterns throughout the entire life span of this species. Relationships of somatic growth were evaluated by weight, length, and age comparisons while muscle growth was assessed from cross-sectional area measurements of white muscle fibers. The average cross-sectional fiber area increased from approximately 150 &mgr;m(2) to 4300 &mgr;m(2) as the fish increased in size, indicating that hypertrophy plays an important role in growth. Hyperplastic fiber recruitment accounted for approximately 93% of muscle growth in recently hatched fish and gradually decreased with fish length. Although the contribution of hyperplasia declined to less than 1% in the largest subject, the persistence of hyperplasia at standard lengths equal to or greater than 91.8 cm as observed in the white seabass has yet to be documented in other fish species. This sustained fiber recruitment may be responsible for the impressive ultimate standard length of 133 cm (41 kg) that white seabass are capable of attaining. The white seabass currently represents the largest marine fish species for which the dynamics of muscle fiber growth have been described. J. Exp. Zool. 284:299-308, 1999. Copyright 1999 Wiley-Liss, Inc.