Reproductive Characteristics of topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel, 1846) in the reservoirs of warmwater fish farming- Golestan province

Topmouth gudgeon (Pseudorasbora parva) is considered as an exotic fish for inland waters of Iran. This study was carried out to investigate some reproduction characteristics of this species in some reservoirs of warmwater fish farms in Gonbad-e-Kavous, Iran.A total of 554 fish samples were collected between March and August 2017 using beach seine, and fixed into 10% formalin. The sex ratio was unbalanced in favoure of females, additionally there was a monthly variation in sex ration. Based on GSI results, reproductive season of this species was April-May, the highest GSI was observed in April. The absolute fecundity ranged between 365 and 1262, and the relative one 104 to 625 egg/g. The absolute fecundity had significant positive relationship with fish size (length, weight and age), while relative fecundity showed a negative correlation with fish size (length, weight and age). Egg diameter ranges 0.37 to 0.93 mm, with an average of 0.71-0.74 mm in different reservoirs.