Relationships Between Body Condition Indices and Proximate Composition in Adult Walleyes

Abstract

Relationships between indices of condition and measures of proximate body composition were examined among and within nine populations of mature walleyes Sander vitreus that varied widely in growth rate and lipid status. Body condition, measured as the residuals from mass versus length regressions, was negatively related to mean water content and positively related to mean lipid content among populations. When the roles of water and lipid content were examined simultaneously within populations, most of the variance in condition was accounted for by lipid content. The strength of the relationships between various condition indices and body proximate composition varied considerably among populations but less between sexes within populations. Furthermore, the strength and nature of these relationships was not strongly influenced by the choice of mass-at-length index (residuals, relative condition, relative weight, or Fulton's K). The visceral-somatic index and muscle lipid content both exhibited slightly stronger relationships with body proximate composition than did mass-at-length condition indices for both sexes. The hepatosomatic index was more consistently related to somatic lipid content for females than for males in most populations. Relatively simple condition indices can provide reliable surrogates of body proximate composition in many adult walleye populations, but caution should be exercised in extrapolating from condition-composition relationships among populations.