Proposed Empirical Standard Weight Equation for Brook Chub Squalius lucumonis

Relative weight (Wr) 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 [Ws]). 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 (Ws) equation by means of the empirical percentile method. The Ws equation thus obtained (log10Ws = –7.75 + 5.75 log10[total length {TL}] – 0.66 [log10TL]2; TL range of application = 90–210 mm) was not biased by length and is recommended as a way to compute Wr for brook chub.