One of this year’s recipients of William and Mary’s Plumeri Award for Faculty Excellence is our own Dr. Patty Zwollo. The Plumeri Award acknowledges those faculty exhibiting passion, vision, and leadership in their teaching, research and service to the College. Since her arrival in 2007, Dr. Zwollo—true to the award—has maintained a passionate drive in both research and teaching in her chosen field of immunology. Specifically, her interests lie in the immune systems of salmonid fishes that exhibit remarkable similarities to mammalian systems with respect to lymphocyte types and antibody diversity.
Dr. Zwollo’s recent discoveries about immune systems and homing behavior by salmon should improve sustainable aquaculture in Alaska. As background, picture yourself in the middle of a vast and unfamiliar wilderness. Now imagine finding your way back home without Google Maps, a GPS tracker, or even trail markers. While this may seem an impossible task to those of the digital age, salmon have been finding their way back home without iPhones or GPS tracking devices for millions of years. So how do they do it? Although salmon may use tide, temperature, and even magnetic fields to assist navigation, their drive to travel all the way back to their birthplaces to spawn appears linked to the development of the salmon’s immune system.
Dr. Zwollo argues in a recent study that because the immune systems of the salmon developed near the germs in their natal rivers, they can fight off the local diseases, which is why they consistently return home to spawn. The salmon that return home are more likely than strays to survive because of the strength of their immune systems at these locations. Immune system memory actually is very common in mammals and much rarer in fish. Usually the cells needed for immune memory are stored in bone marrow, Zwollo has discovered salmon—that notably lack bone marrow—store these cells in their anterior kidney instead.
Dr. Zwollo’s research on salmon immune systems may provide insight into foreseeable problems with ocean ranched salmon. Ocean ranching is a process whereby aquaculturists strip wild salmon of their eggs and sperm, fertilize the eggs in a lab, and raise the salmon in nearby rivers until they are mature enough to join their wild cousins in the open ocean. The rivers where these fish are raised become their lifelong home-bases. Two to three years after leaving their home-rivers for the ocean the salmon reach their reproductive stage and return to where they were raised. This mimics the life cycle of wild salmon that spend their juvenile years in freshwater rivers, leave for the ocean to feed and grow, then return to their home-bases to spawn. During the salmon’s upstream run home, fishermen harvest the lab-bred fish and the wild fish together.
High density salmon populations from hatcheries can put pressure on wild salmon, which causes greater competition for resources and a less healthy environment for the wild fish to mature and breed. Also, because labs typically use the same eggs and sperm to hatch the salmon that will eventually infiltrate the wild fish population, the overall salmon population has lost important diversity in its gene pool. Lower genetic diversity in salmon populations can translate into weaker immune systems among individuals. In fact, cold-water diseases recently have taken a large toll on salmon populations in Alaska, and salmon susceptibility to these diseases may be the result of the population’s weakened immune system. The effects of ocean ranching aquaculture on wild salmon populations that share breeding grounds with the hatcheries must be understood if we want to consume healthy, delicious fish sustainably.
The fate of the wild salmon population may be in question, but one thing we do know about these resilient fish is that there are few upstream battles salmon cannot face. With Plumeri awardee Dr. Zwollo on their side, how can they lose?