Are Hatcheries Producing Triploid Trout?

January 31, 2013

Question: A friend told me  state Fish and Wildlife fish hatcheries are now producing and stocking triploid fish. Is this true? (Anonymous)

Answer: Yes! These vivacious, catchable, sterilized rainbow trout are produced by California Department of Fish and Wildlife (CDFW) fish hatcheries. Triploid fish have an extra set of chromosomes (3N) as a result of pressure treatment, combined with carefully monitored temperature and time precision during egg fertilization. The resulting fish are sterile, making them a more ecologically sound option for recreational fishing in many waters across the state. The fish perform for anglers like a diploid (fertile) fish, many grow larger than the fertile diploids, and they are increasingly being produced in other states for recreational stocking throughout the country.

In fact, new legislation that went into effect January 1, 2013 requires the CDFW to sterilize nearly all fish planted for recreational purposes. This sterilization practice has been in place for decades and requires no manipulation of the cell genomes – no genes are modified or transferred in this process. The carefully applied pressure during fertilization simply encourages the retention of an extra set of chromosomes normally in the egg but later discarded. Polyploidy (more than two sets of chromosomes) is common in the animal kingdom.