Production of a YY Male Brook Trout Broodstock for Potential Eradication of Undesired Brook Trout Populations

Abstract Brook Trout Salvelinus fontinalis introduced outside of their native range often negatively impact native aquatic fauna or provide marginal fisheries and are frequently targeted for manual or piscicide removal in lakes and streams. Unfortunately, complete eradication of exotic Brook Trout populations via these methods is rarely achieved; new approaches are needed. A potential alternative is a Trojan Y Chromosome (TYC) program in which hatchery‐produced genetically YY male fish would be regularly released into an undesired population over time, skewing the population towards 100% males, theoretically resulting in wild population extirpation. We developed two genetic sex markers for Brook Trout and employed juvenile sex reversal methods commonly used in commercial aquaculture to develop a YY broodstock that can produce offspring for possible future use as biological control agents. Our search for genetic sex markers proved successful, with genotypic sex determination for two assays matching the observed phenotype for 90 out of 90 individuals. In the first phase of the program, estradiol‐infused feed readily feminized genetic XY males into neofemales (F XY fish) at a high rate (99.6%; n = 224). Survival of progeny from such egg‐laying F XY fish averaged 88% to eye‐up and 91% from eye‐up to ponding, values similar to untreated Brook Trout reared at the same facility. In the second program phase, we cultured both sperm‐ and egg‐producing supermales (YY fish), a vital step towards development of TYC technology on a large aquaculture scale. Results showed that, in the hatchery, estradiol treatment does not reduce Brook Trout growth. This study demonstrates that hatchery production of a YY Brook Trout broodstock is feasible, modest in cost (less than US$10,000), and can be completed in 4 years. Although several hurdles remain before a full‐scale stocking program could occur, we believe that future work on the TYC strategy for Brook Trout is warranted.