Reproductive biology of Aphanius isfahanensis in the Zayandehrud River, central Iran

Reproductive characteristics of Aphanius isfahanensis, an Iranian endemic Cyprinodontid fish in the Zayandehrud River were examined. Samples were taken monthly, from June 2016 to May 2017. Some 485 specimens (245 females, 240 males) were caught by a hand net. Age of males and females ranged from 0(+) to 2(+) years. The largest female and male in total length and weight was 5.36cm, 2.39g and 4.49cm, 1.56g, respectively. The overall sex ratio was 1M:1F (p>0.05). The highest mean gonadosomatic index in females and males was in May (19.19), and July (3.77), respectively. Oocyte diameter ranged from 0.12 to 1.40mm, and monthly mean oocyte diameter were significantly different (P<0.05). The minimum, maximum, and average absolute fecundity was 7, 250 and 120 +/- 5SD, respectively. The relative fecundity was 90 +/- 30 egg/g body weight. Macroscopic analysis of gonads and gonadosomatic index (GSI) values showed that spawning of A. isfahanensis occurs from April to July with a peak in May and June. Aphanius isfahanensis is a group synchronous spawner and produces more than one oocyte clutch in a single reproductive season.