Heat and chemical treatments in adult Cyprinus carpio (Pisces cypriniformes) rapidly produce sterile gonads

•Adult common carp Cyprinus carpio reared at 38 °C water temperature for 10 weeks with 2-week interval injection of cytotoxic drug busulfan (40 mg/kg; 5 doses in total) produce sterile gonads.•Adverse effects of drug on the animal health was not observed during the study, even after injecting five doses of 40 mg/kg busulfan.•The change of gonads colouration into black appears to be an additional useful index to measure the sterility in teleost fishes.•The treatment protocol for induction of sterility in male and female adult common carp described here will have profound implication for germ cell transplantation in adult fishes.

Several options have been proposed for eradication of germ cells (GCs) in mammals such as treatment with cytotoxic drugs, irradiation, cold ischemia and hyperthermic treatment. Some of these methods have been also tried in fish but conditions for complete sterilisation of gonads have not been established. Here, we report the production of sterile adult common carp Cyprinus carpio in 10 weeks by the heat and chemical treatments. The cytotoxic drug busulfan (40 mg/kg) was intraperitoneally injected into the animals at 2-week intervals (5 doses in total), and they were maintained in water at 38 °C between Weeks 1 and 10. The effectiveness of the treatments was assessed using gonadal index, histology, and vasa gene expression. At the end of Week 10, very severe gonadal degeneration was observed in fish treated with the heat-chemical combination, and 100% of male and female fish were devoid of endogenous GCs. The average levels of vasa transcript were 0.01 ± 0.005 and 0.02 ± 0.016 for males and females, respectively. By contrast, high temperature alone caused minor gonadal degeneration and the gene transcript were 0.59 ± 0.131 for male and 0.62 ± 0.13 for female. In Week 20, after the recovery period of 10 weeks at 25 °C, the gonadal germ cell did not recover from the sterile condition in any of the sampled individuals. The change in colouration of gonads was an additional useful index of the degree of gonadal sterility.