Relative Condition Parameters for Fishes of Montana, USA

Body condition indices are commonly used in the management of fish populations and are a surrogate to physiological attributes such as tissue-energy reserves. Relative condition factor (K_n) describes the condition of species relative to populations in a geographic area. We developed models to allow for the calculation of K_n in Montana, USA by using the weight–length data collected by Montana Fish, Wildlife & Parks. We generated log₁₀weight–log₁₀length relationships to obtain Montana specific parameter estimates for relative condition equations (W′) for 51 species and three subspecies. We developed separate models by water type (e.g., lotic and lentic) and sex for five species due to varying growth based on sexual dimorphism and varying ecosystem types. Relative condition offers the advantage of describing body condition relative to species in Montana, provides a condition index for species that do not have standard-weight models developed for relative weight (Wr), and affords more information for the global database on weight–length relationships of fishes.