My science classes are participating in the University of Alaska Cooperative Extension Service 4-H Natural Resource and Youth Development Program. This wonderful organization offers schools like ours the opportunity to raise salmon in their classrooms. The university provides all the equipment and training. The salmon in Alaska are a precious natural resource, carefully monitored and protected by the Alaska Department of Fish and Game who graciously permits us to use the eggs for educational purposes. We are raising Coho salmon, or silvers as we call them here.
Salmon are anadromous, meaning they are born in fresh water, travel downriver to the ocean where they live out their adult lives, then return to their fresh water birth streams to spawn and die. Salmon need cold, clean oxygenated water to propagate their species. They pass by our village, heading upriver looking for the streams of their origins. It is unclear how they instinctively know where they were born.
Salmon are cold-blooded, so you can control their metabolism, or growth rate, by controlling the temperature of their environment. Biologists monitor the amount of heat salmon eggs are exposed to over time and report this in accumulated thermal units, or ATU’s. Silver salmon hatch somewhere between 400 and 500 ATU’s. You will see the ATU’s reported in the journal entries below. I hope you will enjoy the anticipation of the hatch as much as we will. We should reach 400 ATU’s on the last day of school before the holidays. That might be unfortunate for us as watching the hatch is very exciting. But based on our results last year, I believe the hatch will occur closer to 500 ATU’s and that will be just about when we return from the holidays.
By the way, all the interesting rocks in our tank were collected by us around our village. Hope you enjoy the posts!
Nov 19, 2012. Our eggs arrived in the morning in good condition with 276 ATU’s. We added them to the tank. The water temperature was 5 C. The pump and chiller were in good working order. The eggs were frosty pink and looked healthy. We added rocks to the basket to hold it down because the eggs are neutrally buoyant and have a hard time staying put. We keep the tank covered with insulation to better simulate the naturally dark habitat of the salmon nest, and also to keep the tank as cold as possible in case of a power outage, a common occurrence in rural Alaska. We are fortunate to have a battery backup for our tank to keep our chiller operating if we lose power, so I believe we are relatively safe. There is some foam on top of the water created by the aeration pump.
Nov 29, 2012. ATU’s 326. Temperature 5 C. There was substantial foam on the water so we replaced 5 gallons today. Much of the foam is the result of waste products from the eggs. The shells are semi-permeable membranes that allow oxygen to pass into the eggs and waste products to pass out. Before we exchanged water, we treated the new for chlorine and chilled it to the same temperature of the tank. That’s easy when the temperatures are always well below zero outdoors; you just set the bucket outside for a bit. About 15 eggs have turned milky looking, so they are dead. This sometimes happens if the casings rupture and water penetrates the shell. Today we removed healthy and dead eggs and observed them under the microscope. The dead ones appeared blotchy, with mottled opaque areas that may be congealed fats. The healthy eggs are fascinating; you can see the baby salmon squirming every few seconds surrounded by cheery red globules of proteins and nutrients.