Saugeye, a hybrid of walleye (female) and sauger (male), is a highly popular sport fish, produced and stocked for recreation in 12 U.S. states. Because of its popularity, market potential, and traits well-suited for aquaculture, Saugeye has been identified as a priority species for aquaculture development in North-Central U.S. (NCRAC, USDA). Barriers that have prevented Saugeye aquaculture establishment include reliance on wild broodstock as source of gametes and potential of escapees to contaminate wild gene-pools of wild stocks of parental species. As part of the overall goal of establishing Saugeye as a species for aquaculture, we aimed to conduct the first investigation of Saugeye domestication (production and evaluation of second-generation hybrids) and development of conventional polyploidy methods and innovative genetic manipulation techniques (stem cell transplantation) to produce tetraploid (4n) Saugeye, which can be crossed with normal diploid Saugeye to produce sterile triploid progenies with low costs, and high yields.
We first attempted to develop optimal physical shocking conditions to produce the first 4n Saugeye. In spring 2022, five different shock types were tested: 1) Pressure shocks at 3 different intensities, each applied at 2 different times post fertilization; 2) 2 heat shocks of different intensities applied at the same time post fertilization; 3) a long (120 min) cold shock applied 4 minutes post fertilization (mpf); 4) double shock consisting of a long (120 min) cold shock applied 4 mpf followed by pressure shock applied at 2 different times post fertilization; and 5) double shock consisting of the long initial cold shock followed by a second cold shock. Control, non-shocked, diploid siblings were produced alongside. All shock treatments produced viable hatched larvae except a pressure shock of 9000 PSI applied at 260 mpf. Flow cytometry was used to determine ploidy of first-hatched larvae. Of the 14 shock protocols tested, 3 produced tetraploid individuals, though induction rate was low (7.7-20%). Triploidy was induced in 6 of the 14 protocols, and mosaic individuals (2n and 4n) were observed in 3 treatment groups. Surviving larvae from each treatment group were stocked to separate 37L aquaria within a recirculation system for first-feeding and grow-out to early juvenile stage. Once fish reached 7 months of age, they were transferred to 60L flow-through tanks for further grow-out. Survival and growth were monitored throughout and will be reported.
Next steps will include further refinement of shocking protocols to induce tetraploidy, production of second-generation hybrids in spring 2023, and evaluation of their survival, growth, and overall quality compared to that of traditionally produced, first generation Saugeye hybrids.