2013-14 EMS Outbreak in Chinook salmon
We had lost around 100 eggs this year in our hatching. The eggs that died from natural causes were from eggs that ruptured in the hatching process.
After Thanksgiving Break all of our salmon had hatched and were swimming at the bottom of the tank. However, day by day we lost a few fish. Sometimes we would come back from the weekend and we would have 10-15 passed away at the bottom of the tank. At first we thought we were doing something wrong, but nonetheless, other teachers were reporting the same patterns.
Over Winter Break we lost around 30 fish and they were dying more and more as the days went on. We began feeding those that still looked strong and turned the temperature water up to 52 degrees. The feeding and dying fish were beginning to create nitrates and nitrites in the water and we started doing daily to weekly water changes. By January 20th we only had 15 fish left. Half of them were laying on their sides on the bottom of the tank.
After Thanksgiving Break all of our salmon had hatched and were swimming at the bottom of the tank. However, day by day we lost a few fish. Sometimes we would come back from the weekend and we would have 10-15 passed away at the bottom of the tank. At first we thought we were doing something wrong, but nonetheless, other teachers were reporting the same patterns.
Over Winter Break we lost around 30 fish and they were dying more and more as the days went on. We began feeding those that still looked strong and turned the temperature water up to 52 degrees. The feeding and dying fish were beginning to create nitrates and nitrites in the water and we started doing daily to weekly water changes. By January 20th we only had 15 fish left. Half of them were laying on their sides on the bottom of the tank.
We contacted the Wolf Lake State Fish Hatchery about our loss of fish. Wolf Lake informed us that Early Mortality Syndrome (EMS) is high in the salmon this year. The fish within the hatchery have been pre-treated for EMS by enhancing the water with thiamine, also known as vitamin B1. EMS is caused by this deficiency in their diet, or in this case, a deficiency in their parents' diets. Wolf Lake decided to raise a portion of their salmon this year in their Health Lab which is a tank room that is separate from the rest of the hatchery. In these tanks, they did not treat the salmon for thiamine deficiency. They told me on the day I visited that they lost 40% of their population to EMS this year. When you think of this in the big picture, this means almost half of all the Chinook salmon this year in the Great Lakes produced eggs that had a Vitamin B1 deficiency. Why is this?
Last year the Michigan DNR lowered the stocking numbers of salmon in the Great Lakes because the invasive species, the alewife (which is pictured on the left), had numbers that had dropped as well. The alewife is the main reason the Chinook were introduced into the Great Lakes. However, the spring release of the Chinook was based on the summer prior's numbers. The alewife population actually rebounded last summer and the Chinook were eating a diet of 100% alewives. Which is fabulous! The invasive species was being controlled by the salmon and our Chinook had lots to eat. But this does not mean good things for the diet of our Chinook because alewives are nutrient deficient in Vitamin B1 themselves. If the salmon only eat alewives and not supplement their diet with other fish to get their Vitamin B1, they will produce eggs that will not survive due to this deficiency. This is why we had such a loss of fish in our classroom. Our parent Chinook were deficient in Vitamin B1 (thiamine)
After learning all this at Wolf Lake, we received another 50 fish to add to our tank to supplement the remaining 6 fish in our tank that did not have EMS. These 50 fish came from the Health Lab test tanks. These fish were the 60% survivors of their test batch of Chinook. We can therefore say we know these are healthy fish that did not have EMS originally and were not pre-treated with Vitamin B1 in the water. Below is the video of me placing the new salmon in our tank and getting them acclimated to the water. The second video is the releasing of them in the tank.
Links to Early Mortality Syndrome and Alewives
Chinook Salmon in the Great Lakes
Alewives in the Great Lakes
Salmon in the Classroom- Early Mortality Syndrome in Chinook salmon
Chinook Salmon Information
Alewives in the Great Lakes
Salmon in the Classroom- Early Mortality Syndrome in Chinook salmon
Chinook Salmon Information