https://phys.org/news/2018-10-canadian-californian-rainbow-trout-higher.html

Researchers from the University of British Columbia studied three strains of rainbow trout, one that originated in California and two native to Canada. They found that young fish (called "fry") from California were able to tolerate higher water temperatures and low-oxygen environments better than fry from Canada. There was no noticeable difference in tolerance levels as a whole among adult fish of the same strains. However, individual adult fish from all strains had varying heat and oxygen tolerance levels, with some individuals being hardier and others more vulnerable to climate stressors. "These differences represent naturally occurring variation," said Nicholas Strowbridge, first author of the study. The hardier fish "are just a bit more able to handle high temperatures and low oxygen," Strowbridge explained.

Taking advantage of the natural variation in individual rainbow trout constitution can serve two beneficial purposes. Singling out the stronger fish in hatcheries may help preserve rainbow trout species and also support the global recreational fishing industry as warming trends continue.

                                                            
                                    
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