Proposed Empirical Standard Weight Equation for Brook Chub Squalius lucumonis

Relative weight ( W r ) is an index of condition that enables evaluation of the well‐being of fish by comparing the actual weight of a specimen with the ideal weight of a specimen of the same species and the same length that is in good physiological condition (i.e., the standard weight [ W s ]). This index was primarily developed to assess the status of sport fishes. Recently, however, many authors have encouraged the use of this index as a fisheries assessment tool for nongame species as well, especially those that are endangered or threatened. Length and weight data on brook chub Squalius lucumonis , an Italian endemic species listed as endangered by the International Union for the Conservation of Nature, were collected across its area of distribution and used to compute a standard weight ( W s ) equation by means of the empirical percentile method. The W s equation thus obtained (log 10 W s = –7.75 + 5.75 log 10 [total length {TL}] – 0.66 [log 10 TL] 2 ; TL range of application = 90–210 mm) was not biased by length and is recommended as a way to compute W r for brook chub. Received October 11, 2011; accepted January 12, 2012