• Keast, Allen
  • Eadie, John


Growth in the first summer of life was compared in nine coexisting fish species with different life history strategies. Relative to hatching size, the various species grew 6- to 10-fold in length and up to 1000-fold in weight. Growth patterns were similar among species; length increments were linear early in the summer and reached a plateau by early September. Few species grew significantly in length or weight beyond September. There were also few appreciable differences in length–weight regressions among species, and in all cases growth was isometric. Spawning date had the greatest influence on the amount of growth attained, with early spawners achieving a greater mean length and weight than late spawners. Adult size did not influence the amount of growth; large-bodied species achieved proportionately less of their adult weight and length in the first summer than did small species. However, adult size did influence the duration of the spawning period. Small-bodied species had the most protracted spawning seasons and the greatest size range of young at the end of the summer. There was no apparent relationship between diet type and growth in young fish.


The study was carried out in 1977 in Lake Opinicon, a 2200-ha eutrophic lake in Leeds County, Ontario. Inshore shallow areas and weed beds were netted at weekly intervals from late June to the 3rd week in August. Additional collections were made in early September and early October. Fish were sampled using a 7 x 2 m bag seine net with a 0.15-cm bar mesh. Sixty to eighty individuals of each species were sampled during each collection. Total lengths of all fish were measured. Weights were taken only in September and October in order to determine (i) when weight increments ceased, and (ii) the total weight gains for the summer. 'The data were based on fresh specimens. Water temperature data was collected with a Lambrecht continuously recording thermograph located 3 m offshore in water 1 m deep with the bulb 45 cm below the surface. Data on spawning periods of the fish for the study year are summarized in Duckworth ( 1978) and Keast (I 980). Data on egg size at spawning for each species are from unpublished data and ~r.-f Brown of Queen's University (personal communication). Total body lengths of centrarchid larvae were obtained from individuals captured on the nest. Similar measurements for the remaining species are from the literature (especially Duckworth 1978). These lengths should be regarded as approximations of the length at hatch and used only as a relative starting point to growth. Lengths and weights for Lepomis and Ambloplites at the end of the second summer and at the time of the first spawning (i.e., sexual maturity) are from Keast (1977, 1978) as well as from unpublished data. Female weights are used as the basis of the comparisons.

Changes in total length and weight distributions of young fish were compared using Kolmogorov - Smirnov two-sample tests (Siegel 1956). Length- weight regressions were calculated using model 1 (geometric mean) regression. since both independent and dependent variables were measured with error (Ricker 1973; Sokal and Rohlf 1981). Comparisons between variables were done using Spearman rank correlations (r,) (Siegel 1956).