Abstract
Biologists have theorized that stocking YY males (created via in‐hatchery hormonal sex‐reversal and selective breeding; hereafter M YY fish) could be used to eradicate unwanted non‐native vertebrate populations, but little is known about the fitness of M YY individuals once released into the wild. We compared growth and body condition of stocked hatchery‐reared M YY brook trout ( Salvelinus fontinalis Mitchell) to wild conspecifics in two streams and two alpine lakes. Maximum age for wild fish was age 6 at one stream and age 4 or 5 at the remaining waters, whereas for hatchery M YY fish, maximum age was age 5 at one stream and age 4 at the remaining waters. Total length ranged from 103 to 359 mm for wild brook trout and 115 to 353 mm for hatchery M YY brook trout. Growth rates and body condition of stocked M YY brook trout did not differ from wild fish in the same waters. Given that the success of M YY eradication programs is primarily contingent upon M YY individuals having fitness characteristics similar to wild conspecifics, our results provide further evidence that the stocking of hatchery‐reared M YY fish may be a viable tool for eradicating unwanted non‐native fish populations.