Relationship of Lipid Content to Size and Condition in Walleye Fingerlings from Natural and Aquacultural Environments

Abstract

Condition indices are widely used in the evaluation of fish populations, but most research on the relationship of condition indices to body composition has taken place in laboratory environments. Our objectives were to assess the relative ability of measures of size and three versions of condition index to predict the lipid content of fingerling walleyes Sander vitreus from aquacultural or natural environments. Fingerlings were either intensively cultured through the fall of 1994, were stocked and spent 3–4 months at large in four lakes, or were intensively cultured and maintained overwinter in hatchery ponds. Variation in condition indices accounted for less than 35% of the variation in lipid. No index performed substantially better than the others. The relationship of condition to lipid content was not consistent between environments or seasons (ANCOVA: F = 403.4, P < 0.0005). Relationships were also different among the four lake populations (ANCOVA: F = 33.9, P < 0.0005). Inconsistencies seem to be the result of differences in seasonal and environmental stress. The utility of condition indices as surrogates for body composition should be verified with each use. Furthermore, comparisons of fingerlings from aquacultural environments with fingerlings from natural environments are unlikely to be physiologically meaningful.