Differences in the age at first maturation, as well as timing and magnitude of growth (body and gonad) were examined for northern pike Esox lucius from three lakes in Michigan. The lakes varied in latitude (42 to 46°N), ice-free season (210 to 248 days), and total mortality (Z = 0.28 to 0.85). Body and gonad calorific equivalents were similar among all three lake populations. Male and female northern pike from all lakes and age classes 1–3 had significant accumulation of somatic energy during summer and winter and depletion of reserves over spawning. Testicular growth occurred entirely in the summer, whereas ovarian growth occurred mainly over winter. Females invested 6- to 18-fold more energy into gonads than did males. Total winter growth was significant in both sexes and all lakes. Individual body and gonad growth over the first 3 years of life for northern pike varied little among lakes. Age at first maturation varied significantly among lakes; the earliest maturation occurred in the lake of intermediate latitude, the latest in the southernmost lake. These differences did not correspond well with length of the growth season. However, there appears to be a relationship between total mortality (due to differences in fishing intensity) and proportion of fish mature at age 1. Increased fishing intensity may have induced higher total mortality rates, earlier ages at first reproduction, and higher total energy allocations to reproduction at earlier ages among these populations. Latitudinal differences in climate had little or no apparent effect on growth and reproductive characteristics of the populations.