Morpho-histological characteristics of gonads and reproductive index in an endemic fish species, Oxynoemacheilus persa (Heckel, 1847) (Teleostei: Nemacheilidae) from Kor River basin, Iran

This study presents the first details on morphological and histological characteristics of gonads, gonadal development stages and reproductive index of the Persian loach, Oxynoemacheilus persa (Heckel, 1847), an Iranian endemic species. Sampling was done from April 2010 to April 2011 using electrofishing device and a total of 196 individuals were collected. The gonads of specimens were removed, their sexes determined and then were fixed in 10% formalin solution after checking their morphology and measuring their weights, lengths and widths. Based on the size, shape and weight of the gonads, degree of occupation of the body cavity, presence or absence of ripe oocytes or milt, diameter of the oocytes in the ovary, and histological observations, five stages of sexual maturation in females and four stages in males were determined by macroscopic and microscopic criteria. The results of the gonadal stages showed that the O. persa spawns in the middle of spring and these stages were correlated to the gonado-somatic index (GSI).