Condition Factor

Fulton's condition factor (K) is calculated as K = 100 × W / L³ (where W = body weight in grams, L = total length in cm). It compares the actual weight of a fish to the expected weight for its length, providing a relative index of nutritional status, reproductive investment, or parasite burden. A K value around 1.0 is considered average for most species (varies by species — always compare within species). High K indicates a well-fed, healthy individual. Low K indicates food deprivation, disease, or approaching spawning (when energy reserves are depleted). Condition factor declines predictably in spawning salmon as they invest energy in gonadal development.

Condition factor is routinely measured in stock assessment (to monitor population nutritional status), aquaculture (to assess feed management), and ecology (to study prey availability effects).