Milt production in common carp (Cyprinus carpio): stimulation by a goldfish steroid pheromone

This study examined the effect of a putative steroidal pheromone, 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P) on milt volume and serum gonadotropin-II in precocious male common carp (40–285 g). 17,20β-P significantly increased both milt volume (14–18 h post-exposure) and GtH level (90 min post-exposure) at both doses tested (5 × 10−11 and 5 × 10−10 M in aquarium water), whereas a conjugated form of 17,20β-P (17,20β-P-sulphate) was ineffective at the only dose tested (5 × 10−11 M). Increases in milt, packed sperm volume, and GtH following exposure 5 × 10−10 M 17,20β-P also were compared to those induced by injection of Ovaprim (Syndel; mixture of salmon GnRH analogue and dopamine receptor antagonist) at two doses (0.1 and 0.5 ml/kg body weight). Increases in milt and GtH induced by the high Ovaprim dose were significantly greater than those induced by 5 × 10−10 M 17,20β-P. Increases in milt, and packed sperm volume, and GtH induced by the lower Ovaprim dose were not significantly larger than those induced by 17,20β-P. The results suggest: (1) in common carp, 17,20β-P has a pheromonal role in milt production similar to that demonstrated in goldfish; (2) waterborne 17,20β-P might be a practical non-invasive technique for enhancing milt production in cultured common carp.