“…Endogenous opioid peptides have been shown to be involved in the regulation of several physiological functions, including reproduction, in different vertebrates (Ciarcia et al ., ; Facchinetti et al ., ; Faletti et al ., ; Ganesh & Yajurvedi, ; Leadem & Kalra, ; Olson et al ., ; Polzonetti‐Magni et al ., ; Zerani & Gobbetti, ). Among fishes, treatment with an opioid peptide, β‐endorphin (β‐EP), inhibits the function of the pituitary–ovary axis (Chabbi & Ganesh, ; Ganesh & Chabbi, ), whereas a dose‐dependent stimulatory as well as an inhibitory effect of leucine enkephalin on reproductive axis is demonstrated in the cichlid fish Oreochromis mossambicus (Peters 1852) (Vijayalaxmi & Ganesh, ). Dynorphin is another class of opioid peptide, which is produced from the prodynorphin gene and exists in different forms such as dynorphin‐A (DYN), dynorphin‐B and β‐neoendorphin, among which dynorphin‐A (1–17) is highly conserved and most potent (Civelli et al ., ; James et al ., ).…”