World Aquaculture Magazine - June 2020

50 JUNE 2020 • WORLD AQUACULTURE • WWW.WA S.ORG over the years so that eggs subjected to pressure or temperature shocks result in 97 percent or more triploid fish. Producing triploid fish in some hybrid species will also increase growth rates, which would reduce the time to obtain trophy fish, as with the hybrid crappie, or less time to market-size, as with the hybrid catfish. White crappie female eggs were fertilized with black crappie sperm. At 3 min after fertilization, eggs were subjected to either 6000, 6500, 7000, 7500 or 8000 psi using a hydraulic press, for 2, 3, 4, 5, 6 or 7 min. The best combination that produced the most triploid hybrid offspring was 6000 psi pressure applied for 2 min. Triploid hybrid crappie were stocked into ponds at 4000/acre to evaluate growth rates were increased compared to hybrid crappie. For hybrid catfish, the production facility wanted a technique that could easily be incorporated into their standard hatchery protocols. Pressure shocks did not meet that requirement, so hybrid catfish eggs were subjected to heat shock following the protocol of Perera et al. (2008). Triploid hybrid catfish were stocked into ponds at 8,000/acre and compared to hybrid catfish. Triploid hybrid crappie and hybrid crappie were feed-trained prior to stocking into ponds. All fish were fed 3 percent of their body weight per day and all groups were replicated four times. Growth rates, FCR, and gonad development were examined after one year. Survival rates for triploid hybrid crappie fry and triploid hybrid catfish fry were greater than those of diploid hybrid crappie and hybrid catfish. Growth rates of triploid hybrid crappie were 10 percent greater than those for diploid hybrid crappie (Fig. 1). Survival, feed conversion efficiency or growth of triploid hybrid catfish was not significantly different from that of diploid hybrid catfish produced in ponds. Reproductive function of first-generation offspring of triploid hybrid crappie and triploid hybrid catfish was significantly reduced with little viable sperm or eggs visible in the gonads. This study demonstrated that triploid induction in hybrid crappie and hybrid catfish produced more offspring and that these offspring were sterile. Triploid hybrid crappie also grew significantly larger than diploid hybrid crappie while no significant difference in growth was observed in triploid hybrid catfish compared to diploid hybrid catfish. I n August 2019, the Executive Director of the National Aquaculture Association (NAA) asked Dave Straus to organize a special producer session for Aquaculture America 2020 to invite experts to give presentations about their research related to sterility in aquaculture. The session was intended to provide information on various methodologies to induce sterility in aquatic species as functional sterility is an important management and production tool for aquaculture in many areas of the United States. The session focused on what works, what doesn’t work and why. The presentations covered traditional non-molecular approaches as well as novel and emerging molecular approaches. Induction of Sterility in Hybrid Crappie and Hybrid Catfish Anita Kelly, Nagaraj Chatakondi, Robert Glennon and Jeff Baxter Hybrid fish are routinely produced for use in commercial aquaculture and to support recreational fisheries. Black crappie Pomoxis nigromaculatus and white crappie P. annularis are popular panfish caught by anglers in the US. Hybrid crappie P. annularis ♀ x P. nigromaculatus ♂ grow faster and weigh more than both parent species. Hybrid crappie are stocked into ponds to obtain trophy- sized fish quickly. One drawback to stocking crappie or hybrid crappie in farm ponds or recreational fishing lakes is excessive reproduction leading to overpopulation. Hybrid catfish are the cross between a female channel catfish Ictalurus punctatus and male blue catfish I. furcatus . Hybrid catfish are produced commercially for the foodfish market. Hybrid catfish grow faster than the channel or blue catfish, have higher survival rates and better meat yield than channel catfish. Hybrid catfish production constitutes approximately 50 percent of the catfish production in the U.S. However, first-generation hybrid catfish can reproduce. Triploid induction is a method used to induce functional sterility in fish. Some of the earliest techniques developed for producing triploid fish involved water temperature or pressure shocks when the first polar body is starting to be ejected from the egg. These two methods of triploid induction have been refined Sterility in Aquaculture — Advances, Performance, Impacts Compiled by Dave Straus FIGURE 1. Hybrid crappie (top) and triploid hybrid crappie (bottom) showing the difference in growth rates. The best combination that produced the most triploid hybrid offspring was 6000 psi pressure applied for 2 min at 3 min after fertilization.