some biological characteristics of sefidrud loach, oxynoemacheilus bergianus (teleostei: nemacheilidae), in aras river, northwestern caspian sea basin

some 190 specimens of sefidrud loach, oxynoemacheilus bergianus , were collected from aras river (northwestern iran) and age, size, and some biological characteristics of the samples were investigated from march to july 2013. the maximum age was 3 + years. the specimens ranged in size from 42 to 64mm for males and 45 to 61mm for females in total length, weighing from 0.62 to 2.03g for males and 0.63 to 1.66g for females. length-weight relationship was estimated as w= 0.00005tl 2.81 for females, w= 0.000005tl 3.11 for males and w= 0.000008tl 2.97 for the sexes combined. sex ratio was 1m:0.9f, in favor of males (p<0.05). the growth model was isometric for males, females and sexes combined. the calculated maximum fulton’s condition factor ( k f ) and allometric condition factor ( k a ) were 0.900 and 0.010 in males and 1.000 and 0.009 in females, respectively. the most frequent age classes in the samples were 2 + years for both males and females. in general, as most other loaches, sefidrud loach is also a small short lived species with a low frequency in aras river.