Production of androgenetic amago salmon Oncorhynchus masou ishikawae with dispermy fertilization

With the aim of improving artificial androgenesis in teleost fishes, we tested two methods for producing androgenetic diploids of amago salmon (Oncorhynchus masou ishikawae), namely, fertilization of gamma-ray irradiated eggs with fused spermatozoa (sperm-fusion method) and the fertilization of irradiated eggs with untreated sperm followed by the blocking of cell division (mitosis-inhibition method). Our results showed that the optimal condition for sperm fusion was to treat the sperm with 50% polyethylene glycol (molecular weight 7500) for 100 s. The efficiency of the two methods of androgenesis was compared in terms of fertilization rate, hatching rate, and larval survival after hatching. The rate of fertilization was lower with the sperm-fusion method than with the mitosis-inhibition method, but the reverse was true for the hatching rate. The survival rate of hatched larvae was the same with the two methods. Androgenesis was confirmed with a recessive albino color marker, and all viable offspring were found to be heterozygous based on analysis of the microsatellite markers. Our results suggest that androgenesis with the sperm-fusion method is a promising approach with potential applications in both aquaculture breeding programs and the preservation of endangered freshwater fishes.