Estimates of the basic population parameters for the upland bully,Philypnodon brevicepsStokell, in Spectacles Lakes from February 1969 to March 1970 are presented. The study population in Small Spectacles could be defined as a discrete, freely‐mixed unit bounded by the edge of the lake, within which individual fish moved extensively in all seasons. Individual fish were regularly spaced with respect to their nearest neighbours but samples taken with both push and trap nets exhibited clumped dispersion. In summer older fish were in deeper water by day but moved to the edge of the lake at night, whereas in winter older fish inhabited deeper water by night. Population numbers and densities were high, ranging from 1.95 million fish (208/m2) in February 1969 to 124 thousand (21/m2) in March 1970. Annual mortality averaged 93 % for all age groups combined but was higher during the early stages of life. Mortality also increased during summer. Recruitment in Small Spectacles was low due to egg resorption by maturing females prior to the 1969 breeding season. Spawning, however, occurred normally in the adjacent lake, Large Spectacles, and egg survival was estimated to be 43.5 %, The growing season, as measured by the monthly change in mean length, extended for seven months of the year (October‐April). No growth occurred in winter. Growth of males exceeded that of females and growth within a year‐class was negatively correlated with the numerical strength of the