Growth energy build‐up and partitioning by immature bluegill sunfish were studied over the summer months from May to September 1984. Fish sampled in May showed low condition and low lipid reserves. Condition was restored to summer levels within the following month. Fat reserves were built up from 7% to 14% of body weight over the entire summer. Most (80%) of the annual length increase occurred from 1 June to 15 August. Over the winter period (October‐April) condition dropped and lipids were depleted. Calculations showed that energy liberated through lipid depletion over this period could supply the energy requirements of inactive wintering fish. It is concluded that the sequencing of growth energy diversion into changes in body length, condition, and lipid build‐up enhances mid‐summer growth and overwinter survival.
Lake Opinicon is a small (22 000 ha) eutrophic lake on the Rideau canal system in southern Ontario. It has an extensive, heavily vegetated littoral zone (Keast, 1984). The bluegill is the most numerous species in the lake; young fish spend the winter period off-shore and the summer in small, shallow bays (Brown & Colgan, 1982). Bluegills were sampled (using seine net) from Cow Island Bay, a small bay on the north-eastern side of the lake, on six occasions during the summer of 1984 (15 May, 16 June, 9 and 31 July, 21 August, and 29 September).