** Authors:**
ŞULE SÜLÜN, SERCAN BAŞKURT, ÖZGÜR EMİROĞLU, DANIELA GIANNETTO, ALİ SERHAN TARKAN, SEVAN AĞDAMAR, ÖZCAN GAYGUSUZ, ZEYNEP DORAK, HAMDİ AYDIN, ARZU ÇİÇEK

** Abstract: **
Indices of condition enable the evaluation of the well-being of fish, with the assumption that heavier fish of a given length are in a better condition. Relative weight (W_{r}) is one of these indices; it is calculated by comparing the actual weight of a specimen with the ideal weight of a specimen in good physiological condition of the same length from the same species, i.e. standard weight (W_{s}). In this research, length and weight data over the distribution range for Pursak chub Squalius pursakensis, an endemic species distributed in the Sakarya and Porsuk drainages in Northwest Anatolia (Turkey), were used to compute a W_s equation by means of the empirical percentile (EmP) method. The W_s equation obtained was log_{10} W_s = -4.657 + 2.614 log_{10} TL + 0.127 (log_{10} TL)^{2}, and the total length range of application was 80-340 mm. Since the EmP W_s equation was not influenced by length variation, the use of this equation to compute the relative weight (W_r) for S. pursakensis throughout its area of distribution is suggested.

** Keywords: **
Condition indices, endemic species, Squalius, relative weight

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