| Summary: | Slimy sculpin (<i>Cottus cognatus</i>) are increasingly being used as indicator species. This has primarily entailed measuring their condition, the assumption being that condition can be used as a surrogate for lipid content. While there is evidence to suggest this assumption is applicable to some fish, it has yet to be validated for <i>C. cognatus</i>. Further, there are several means by which one may calculate condition, the most commonly employed of which are indirect measurements of lipid content (namely, Fulton’s <i>K</i>, somatic <i>K</i> (<i>Ks</i>), and Le Cren’s relative condition factor (<i>Kn</i>)). We compared the ability of each of these morphometric indices to predict whole-body lipid content in <i>C. cognatus</i>. There was a moderate degree of evidence that Fulton’s <i>K</i>, <i>Ks</i>, and <i>Kn</i> are reliable predictors (<i>Ks</i> and <i>Kn</i> in particular). Of the latter we recommend <i>Kn</i> be used because, unlike <i>Ks</i>, it does not require that fish be killed. And while Fulton’s <i>K</i> did not perform quite as well, we consider it a sufficient substitute if the data necessary to calculate <i>Kn</i> are unavailable.
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