Age, sex ratio, spawning season, gonadosomatic index, and fecundity of Cobitis faridpaki (Actinopterygii, Cobitidae) from the Siahrud River in the southeastern Caspian Sea basin

Cobitis faridpaki Cobitis faridpaki (Mousavi-Sabet, Vasil\'eva, Vatandoust and Vasil\'ev, ۲۰۱۱) is found in streams of the Siahrud River in the southeastern Caspian Sea basin, and this is the first report on reproductive parameters of the newly described endemic loach. Reproductive conditions are key parameters of fish populations, and their assessment is very important for endemic fishes. To study reproduction biology of this fish, sampling was done at monthly intervals throughout the year and ۲۵۸ individuals of Cobitis faridpaki, were caught from Siahrud River in the southeastern Caspian Sea basin, in the north of Iran. Age, sex ratio, fecundity, oocytes diameter and gonadosomatic index were estimated. A regression analysis was used to find relationships between fecundity and fish size (length and weight), gonad weight and age. Sex ratio differed significantly from unity and was biased to females. The mature females and males were longer than ۴۰ and ۳۰ mm in total length, and +۲ and +۱ in age, respectively. The average egg diameter was ۰.۵۷۸ mm. Spawning took place from beginning of May to late July when water temperature was between ۱۹.۴ to ۲۵.۱ ?C. Average GSI value at the beginning of the reproduction period was ۹.۱۲% and ranged between ۲% to ۲۰% in ripe mature females. The averages of absolute and relative fecundity were calculated as ۱۳۶۶ and ۵۰۸, respectively. The absolute fecundity was significantly related to body weight and gonad weight. Based on the pattern of gonadosomatic index, it was concluded that this fish has a prolonged active reproduction period, which is a type of adaptation of short-lived small fishes to environmental conditions.

Keywords:

Reproductive biology , Oocytes diameter , Ovary , Loach , Iran