Statolith growth and banding patterns were examined in larval sea lampreysPetromyzon marinuspreviously marked by oxytetracycline injection and held up to 20 months under constant and cycling temperature at either a natural or constant (15 h light: 9 h dark) photoperiod. Banding patterns were not influenced measurably by photoperiod, and statolith growth did not occur when larvae were held at a constant 8°C. Statolith growth at 12°C was even throughout the study and annuli did not form. Statoliths from larvae held at temperatures adjusted to mimic those of a typical sea lamprey stream formed annuli during the simulated winter and early-spring period. The shift in metabolism from protein synthesis to lipid storage that occurs during the final year of larval development did not alter the statolith banding pattern. An annulus was not formed during the nontrophic period of metamorphosis, which is completed by early winter, nor during the first few months of the juvenile period when low ambient temperatures inhibit feeding. Statolith growth increased rapidly in juveniles once active feeding on teleosts commenced. When larval southern brook lampreysIcthyomyzon gageiwere injected with oxytetracycline, and held at the same seasonally adjusted temperatures and photoperiods as larval sea lampreys, they showed the same statolith growth and annulus formation. Prior to marking and exposure to seasonal temperatures more extreme than those experienced in their usual habitat, southern brook lampreys had no annuli on their statoliths. This is consistent with the earlier observation of even larval growth throughout the year in their natal streams.