The Lake Sturgeon (Acipenser fulvescens) continues to grow throughout life, though the process by which muscle stem cells, called satellite cells (SCs) contribute to formation of fibers in the myotome is largely unknown in this endangered fish. Since muscle function and growth are critical to survival, it is important to understand the functional basis of fiber growth, and how SCs provide daughter cells that fuse into fibers in myotome development and regeneration. The hypotheses are that during aging: the cell cycle of SCs lengthens, the ratio of SCs to myonuclei decreases, and myonuclear domain increases. This experiment used the single fiber model and a pulse-chase design in which exposure to bromodeoxyuridine (BrdU) labeled S-phase for the first 2 hr in culture. Myofibers were isolated from 20-40 fish per age (1-6 months post-hatch). After fiber culture for 24 hours, fibers were fixed and stained for BrdU or Pax7 (expressed by myogenic stem cells) with colour detection. The number of Pax7- or BrdU-positive nuclei and the total number nuclei associated were counted per fiber in 8-20 fibers per dish. Results showed a significant change in the ratio of Pax7+ SCs to myonuclei as the fish age (p < 0.05) with an apparent decrease in cell cycle duration with increasing age (p < 0.05). This investigation adds to our understanding of SC contributions to myofiber growth in the developing Lake Sturgeon and results will be a new foundation for future research on the role of environmental influences on muscle in Lake Sturgeon.