World Aquaculture Magazine - June 2020

WWW.WA S.ORG • WORLD AQUACULTURE • JUNE 2020 51 Production of the Gynogenetic Female Walleye and Induction of Sex Reversal with Methyltestosterone Konrad Dabrowski, Mackenzie Miller, John Grayson and Alexander Kramer The Ohio State University’s Aquaculture Laboratory has been working to produce walleye Sander vitreus with superior production traits through the use of induced gynogenesis, triploidy and hormonal sex reversal. This project was funded by the North Central Regional Aquaculture Center (USDA) with the final objective of producing all-female sterile triploid fish. In April 2018, OSU researchers obtained gametes from wild Lake Erie walleye with the help of Ohio Department of Natural Resources (ODNR) personnel on the banks of the Maumee River (Fig. 2). Male and female walleye gametes were then transported to the OSU Aquaculture Laboratory for in vitro fertilization trials to produce gynogenetic and normal control walleye progenies. Walleye eggs were activated utilizing UV- irradiated sperm of yellow perch Perca flavescens and three meiotic gynogen families of walleye were obtained via pressure shock with high efficiency, approximately 7 percent survival to hatching. All progenies were fed live Artemia nauplii as first food and then transitioned to formulated feed. Based on the known XY sex determination system in walleye, researchers then attempted hormonal sex reversal to produce neomales via feeding a methyltestosterone (MT)-containing diet to both gynogenetic and control fish for 50 days once fish had reached 1.5-3.5 g in total body weight. After hormone treatment, fish were then pooled into “common garden” tanks for grow-out (Fig. 3). Gynogenetic fish fed the control diet reached larger size at one and two years of age than gynogenetic fish fed the MT-containing diet. Several walleye males produced motile sperm in 2020 that was examined for its viability. As female walleye had not reached sexual maturity as two-year olds, following UV-irradiation, walleye sperm was used in turn to produce gynogenetic yellow perch. Both of these projects, leading to gynogenetic walleye and yellow perch (in progress) are the first reports in the literature. Further studies will aim to refine this technology for intensive culture of walleye, saugeye and yellow perch, and will continue in collaboration with Ohio fish farmers. Development of Genetics-based Selective Breeding of Sterile Kelp Sergey Nuzhdin and Gary Molano Current aquaculture is limited to native species being farmed in their native ranges, as concerns of invasive species and gene flow between domesticated and wild populations prevent the standardization of crops that was a key component of the Green Revolution. These concerns are justified in aquaculture, as mistakes in the aquaculture industry have led to invasive kelps spreading across Europe. Giant kelp Macrocystis pyrifera is a brown macroalgae that grows rapidly and has a global range. It is a keystone species, providing important habitat for many different organisms, both near the surface and its anchor substrate. Due to its rapid growth and extended range, the Department of Energy identified giant kelp as a domestication target to produce feedstocks for biofuel. Giant kelp has a haplodiplontic life cycle, in which diploid sporophytes produce haploid spores, which develop into haploid gametophytes. These haploid gametophytes then produce eggs and sperm for the next generation of sporophytes. However, this haplodiplontic life cycle can be leveraged for domestication purposes, as the haploid gametophytes can be grown clonally in the lab under specific conditions. This is excellent for domestication purposes, as preferred genotypes can be quickly grown in the lab and specific crosses can be repeated many times over. However, producing high-quality giant kelp cultivars may exacerbate the problems of invasive species and transgene flow between domesticated kelps and wild populations, as domesticated kelp may escape the farm and spread to new habitats or mix with a local population. Therefore, it is paramount to farm productive giant kelp cultivars without any chance of the kelp turning invasive. FIGURE 2. ODNR personnel collecting walleye eggs (dry method, left); water has been added to the bowl containing gametes of both sexes and ODNR personnel are mixing them during fertilization (right). FIGURE 3. Juvenile gynogenetic walleye in a “common garden” grow-out tank. The Ohio State University’s Aquaculture Laboratory has been working to produce walleye Sander vitreus with superior production traits through the use of induced gynogenesis, triploidy and hormonal sex reversal. ( C O N T I N U E D O N P A G E 5 2 )