Abstract
The Sefidrud stone loach/Berg loach Oxynoemacheilus bergianus is native to the Eurasia and little is known about this species. Some biological characteristics of the spices were examined in 358 specimens collected monthly from the Kordan River in Alborz Province, by dip and seine nets during September 2013 to August 2014. The total length range was 32.36-74.36mm (50.95±10.3SD), and the total weight range was 0.31-4.06g (1/12±0.68SD). The maximum age of the specimens, based on otoliths, was 5 + years for females and 4 + years for males. Based on macroscopic gonad observation, the age of maturity was 2 + for females and 1 + for males. Sex ratio was 1M:0.9F, maturation cycle consisted of five stages. The gonadosomatic index indicated that reproduction of the fish in the river system occurred between March and June, with the highest average value of 9.47 for males in April and 13.42 for females in May. Oocyte diameter ranged from 0.15 to 1.33mm, with a mean value of 0.44mm. Absolute fecundity ranged between 360 and 2560 eggs, with a mean of 1130±670 eggs. Absolute fecundity and total length (r 2 = 0.58) and total weight (r 2 = 0.66) were moderately correlated. The mean relative fecundity was 580±190 eggs per gram of body weight. Therefore, O. bergianus is a species with a premature sexual maturity, high fecundity than other loaches and reproduction happen gradually in March to June.
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