Researchers at the Hebrew University of Jerusalem have proved that breeding disease-resistant carp can make fish farming more sustainable and profitable. It can even keep non-resistant fish healthier. The study bred fish with built-in immunity to the common cyrpinid herpes virus that kills 60-80% of infected fish.
https://www.timesofisrael.com/researchers-study-how-to-keep-our-gefilte-fish-healthy/