Aquaculture America 2020

February 9 - 12, 2020

Honolulu, Hawaii

AN EVALUATION OF SEX REVERSAL RECIPES FOR FEMINIZATION OF MALE LAKE TROUT Salvelinus namaycush AND FUTURE DEVELOPMENT OF A YY MALE BROODSTOCK

Daniel J. Schill*, Elizabeth RJM Mamer, Malia Gallagher , Wayne Fowler , Kevin Kincaid and Bryan Grant
Idaho Department of Fish and Game  
1414 E. Locust Lane  
Nampa ID  83686  
Dan.schill@idfg.idaho.gov

Lake Trout populations  in western U.S. waters  have been shown to have adverse impacts on native or desirable fish species and are often targeted for manual removal.  The population in Lake Pend Oreille, Idaho has been successfully suppressed to levels that have permitted the rebound of the primary forage population and more recent use of the same approaches in Yellowstone Lake Wyoming  have allowed native Yellowstone cutthroat  there to begin rebuilding.   Despite these apparent successes, annual suppression costs on these two waters has  recently ranged from 1-2 million annually , amounts far above those available for successful Lake Trout eradication in most other western waters.   Alternative  or complementary  methods that could be used  to  control or  completely eradicate Lake Trout populations  are needed.    YY Males, which are created in the hatchery by feminizing XY males then crossing them with normal XY males, comprise another approach to eradicating undesirable populations. If stocked YY Males survive and reproduce with wild females, it could eventually drive the wild population sex ratio  to 100% males, at which point the population would be unable to reproduce and be eradicated after stocking ceased.  A  sizeable  YY Male Brook Trout  broodstock has been developed and is  currently being  field evaluated by stocking in 16 Idaho waters .  The present study documents the first step in  companion efforts  to develop a YY Lake Trout Broodstock for  similar  wild Lake Trout eradication evaluations .    Lake Trout eggs  were  obtained  on 16 October, 2016  by spawn crosses at the Story Fish Hatchery in Wyoming ,  transferred to the Grace Fish Hatchery in Idaho and placed in Heath trays. Newly hatched fry (n= 120)  were transferred to 24 individual 3.75 gal pots and treated with one of 12 treatmen ts.   Treatments tested included immersion (200-400 microg/L), top-coated feed for 97 d beginning at first-feeding , and immersion-feed combinations involving both Estradiol and Estrone as the feminizing hormone .   Growth and survival were monitored  periodically  and  compared to controls.  Numbers  were culled to 35 fish per tank to prevent overcrowding.   A total of 840 fish  averaging 82.3 mm  were removed  from the 24 pots in June 2017 , PIT tagged and reared in a common garden raceway until sex could be  readily  determined visually.   Mean growth rates (in length and weight), mortality rates, and observed sex ratios f ollowing necropsy for all treatment and control groups will be reported and next steps in development of a YY Lake Trout broodstock discussed.