I think it's safe to assume that people are naturally drawn to lakes, rivers, oceans, and water in general. There is a multitude of reasons behind our natural affinity for water, but if you are anything like me, fishing has a lot to do with it. Fortunately, I grew up within a mile of Laurel Hill Creek in Pennsylvania and multiple lakes and farm ponds that offered excellent fishing which caused me to fall in love with the sport and everything it entails. For me, there is no better escape and way to challenge and enjoy myself in the outdoors. Let’s be honest though, no matter how great the scenery and the conditions may be on a particular day, it is always more fun when you are catching fish! However, some places do not have large, naturally reproducing populations that offer lots of hungry fish that are ready to be caught. So how do we fix this problem? We simply stock more fish in these waterways.
Stocking fish is not a new concept as people have been doing it for centuries. However, before we start dumping fish into every river and lake, we need to address the potential consequences, something we weren’t great at historically. Just look at species like the Asian Carp and Northern Snakeheads and the damage they have caused since their introductions. Additionally, introducing hatchery-raised fish into waterways with naturally reproducing populations of the same species can damage the native species. An example of this would be introducing hatchery-raised rainbow trout into naturally reproducing rainbow trout streams. The problem arises when the hatchery-raised trout try to spawn with the native trout. Hybridization between hatchery and native fish dilutes the genetics of the wild populations which produces succeeding generations that have decreased chances of surviving and reproducing. According to a study by Oregon State University on steelhead in Oregon’s Hood River, steelhead that have at least one parent which was raised in captivity exhibit drops in reproductive success by up to 45%. So if stocking hatchery fish can damage native populations, is there a safer way to still offer great fishing opportunities in areas with limited native populations? Well, thanks to the study of genetics, there is, and it is triploid fish!
According to the California Fish and Game Service, triploid fish are fish that contain three sets of chromosomes instead of the normal two, which in turn makes them sterile and unable to reproduce. To understand how we create triploid fish, a basic understanding of meiosis and oogenesis is required. In oogenesis or meiosis of female eggs, the oocyte is paused in the metaphase stage of meiosis 2 until fertilization by sperm occurs. Once fertilization occurs, meiosis 2 continues and the oocyte and a polar body are formed that both contain a set of chromosomes. The oocyte will complete fertilization to form a diploid zygote and the polar body will degenerate. This is where treatment of the fertilized eggs comes into play. By subjecting the eggs to either high pressure, specifically 10,000 psi for 5 minutes, or heat by placing them in a 79 degree Fahrenheit water bath for 20 minutes, the polar body that is normally expelled is retained. This results in a triploid zygote that will develop into a triploid fish. The technique used differs from state to state as California uses the pressure method while Alaska uses the heat method.
According to the Alaska Department of Fish and Game, one more step is taken to ensure the triploid fish do not reproduce. In their early life stages, female fry are fed male hormones to reverse the sex of the fish and create morphological males that only produce sperm with X chromosomes. This ensures that all the offspring produced are females, and due to differences in reproductive development from males, triploid females have an even smaller chance of successful reproduction.
By creating triploid fish that are sterile, we can now safely stock rivers and lakes with hatchery fish to increase the quality of these fisheries without imposing the genetic risks discussed on the native species in the area, and the benefits of triploid fish don’t stop there. According to the Freshwater Fisheries Society of British Columbia, triploid trout have been shown to live longer and grow larger than their stocked diploid counterparts since they put less energy into gonad maturation and spawning activity. Additionally, all-female, triploid trout exhibit these effects to a greater extent over males as their maturation process is delayed which allows them to put more energy into growth.
So thanks to the creation of triploid fish, we can now safely stock fish, whether for fishing purposes with species such as rainbow trout, or for management purposes, such as vegetation control with grass carp, without the concern of these fish reproducing either with each other or with native species. Thus we are protecting native species and ecosystems from invasions both physically and genetically while enhancing fisheries for our own use and enjoyment. It’s a win-win situation!
Figure 1: Infographic about the Basics of Triploid Fish
I'd be happy to answer any questions at rapst6@student.mtaloy.edu.
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