by Beth Silvy
Ph.D. student Elizabeth Silvy and Professor Todd Sink are looking to change the future of flounder aquaculture and stock enhancement along the Texas coast. A popular recreational game and commercial fish, wild southern flounder stocks are declining. In commercial aquaculture, much of the economic costs come from growing out and maintaining males as broodstock. Male southern flounder grow significantly slower than females and rarely reach market size. Through techniques that have been attempted by researchers at the University of North Carolina, Silvy and Sink are altering southern flounder gender through hormonal manipulation. Silvy is the first to run these techniques side by side using southern flounder.
Flounder broodstock was collected from Sea Center in Lake Jackson Texas, a stock enhancement hatchery that provides juvenile red drum, trout, and southern flounder to locations along the coast for stock enhancement purposes. Broodstock was strip spawned, and then eggs were divided into three treatments. One treatment served as the control, utilizing untreated milt and eggs. Two treatments utilized UV radiated milt mixed with unaltered eggs. The UV irradiated milt serves to fertilize the eggs, but does not provide DNA, ensuring that the larval fish that hatch are gynogenetic clones of the mother. These gynogenetic clones will then be treated with methyltestosterone after hatching to render them phenotypically male, while the flounder themselves remain genetically female. These females can be bred back to “normal” female flounder to produce an all female population of flounder that can be released for stock enhancement purposes. This process eliminates the need for costly male fish in commercial and stock enhancement hatcheries. And since one wild male fish will breed with hundreds of female fish, introducing thousands of female flounder larvae will benefit the recreational and commercial industry. Silvy performed a second round of spawning and treatments over Spring Break.