Reproductive biology of lotak, Cyprinion macrostomum Heckel, 1843 (Pisces: Cyprinidae), from the Tigris River drainage

Some reproduction aspects of the "doctor fish", Cyprinion macrostomum, were examined for the first time from the Tigris River drainage. A total of 316 specimens were caught from Gamasiab River in western Iran, at monthly intervals throughout the year from January to December 2013. Age, sex ratio, fecundity, oocytes diameter, gonado‑somatic (GSI), modified gonado‑somatic (MGSI) and Dobriyal (DI) indices were estimated. Regression analyses were used to find relations between fecundity and fish size (length and weight), gonad weight, and age. Sex ratio differed significantly from unity, and the percentage of males was greater than that of females. The mature females and males were longer than 108 mm and 94 mm in total length (+2 and +1 in age, respectively). The GSI ranged between 0.09-2.94% and 1.70-15.53% for males and females, respectively. Gonad indices showed spawning took place from May to August, when the water temperature was 16 to 24 °C. The average diameter of the oocytes ranged from 0.2 mm to 1.7 mm, in the spawning season. The averages of absolute and relative fecundity (relative to body weight) were 3642.51 eggs (SD ±1219.92) and of 55.04 (SD ±14.12) per gram body weight, respectively. The absolute fecundity was significantly related to body weight and ovary weight.