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From the Greek roots onkos “hook” + rynchos “nose” and kisutch, the common name for coho, or silver salmon in Alaska. The name is not nearly as appealing as their taste. Lift a 30 inch silver out of a salmon wheel along the banks of the Yukon, place it in foil with some herbs and vegetables, cook over hot coals until it is butter smooth, then savor your dinner by the campfire and I guarantee you will forget all about science.
Salmon In The Classroom
Our “Raising Salmon In The Classroom” project started off badly. The eggs were set to arrive Monday at 6:30 pm. and it was important to have the tank chilled and ready for them before they arrived. The Sunday night before, our fish tank broke. Quick – Monday morning emergency calls to Fairbanks! I purchased a new tank over the phone from Petco and arranged for a courier to pick it up and deliver it to the airport. They didn’t expect to be able to fly it out until Wednesday. Oh well. One thing I have learned about life here; nothing is easy in the bush. The Monday evening flight carrying my eggs was expected to depart Fairbanks at 5:30 pm. The keyword regarding bush departures is “expected,” so I called Warbelow’s at 5:35 to see if the “expected” had indeed become a reality. Nope. 6:00 pm, nope. The plane finally landed at 7:30 pm. There were no passengers, it was loaded with freight. I patiently stood in the sub-zero wind watching each box as it was unloaded into waiting pickups. The last box was offloaded. Wait, where are my eggs? I look into the empty plane, ask the pilot if there wasn’t another box addressed to me. Nope. I looked through the two trucks just to make sure my precious eggs had not mistakenly gotten onto one of them. Nope. Snafu, fubar, nothing is easy in the bush. So I tried to call my supplier but the phone network was down and I couldn’t ‘t call out of Fort Yukon. Snafu, fubar, nothing is easy in the bush. I fired off emails, but don’t hear back from them until Tuesday morning. Those fragile eggs that have to be kept chilled but not frozen were mistakenly still sitting in Fairbanks. But I am promised that they will be delivered to Warbelow’s Tuesday morning in time for the afternoon flight. This time things work out and the eggs do arrive at 3:00 in the afternoon. And by some miracle my fish tank actually arrives on Tuesday’s evening flight.
Our tank is now chilled to a salmon pleasing temperature of 6 degrees C and our eggs are incubating on the bottom of our new tank. Our expensive new tank. The eggs are sensitive and I am concerned about the unknown conditions during their Fairbanks layover. But we have done all we can do. Okay, you fishies, live!
November 28 – 422 ATU’s
Well, things are looking up, and our salmon eggs are doing rather nicely. In the picture of the egg basket, you can see a few eggs that have turned white and opaque. They are dead, but most have survived the shock of being shipped off to a new home, and today several have hatched.
Actually, you can estimate, and to some degree control, when the hatching will take place. Salmon are cold-blooded so their metabolism is quite dependent on water temperature. At 4 degrees C salmon will take longer to hatch than they will at 8 degrees C. The temperature to which salmon are exposed is carefully monitored; an average daily temperature of 6 degrees C over a 24 hour period equals 6 ATU’s, or accumulated thermal units. If the temperature holds constant at 6 degrees for 70 days, they will have 420 ATU’s. Coho, or silver salmon as we call them here, will hatch at 400 to 500 ATU’s. Our silvers reached 422 ATU’s today, and we noticed our first eggs hatching. So the kids are learning to make observations, record data and use past experience to predict future events, just like real scientists.
December 16 – 530 ATU’s
We were supposed to receive 500 eggs although I believe the actual number was closer to 400. More than 200 alevin have hatched and appear healthy; its difficult to get an accurate count because the alevin cluster together and wiggle around. Another 60 have died and the remainder are unhatched but viable.
Salmon have a complex life cycle and progress through a series of developmental stages. They begin as eggs and are very fragile at first. Eventually the eggs harden and stabilize and the embryos become large enough that the eyes can be seen through the transparent egg membranes. When salmon hatch they are called alevin and are physically very different from the fish they will become.
December 17 – 536 ATU’s
When alevin hatch, they come out carrying their own supply of food – proteins, fats and salts stored in their yolk sac. The kids call this the lunch bag. As long as they remain alevin, it won’t be necessary to feed them. Eventually, sometime after the holiday, they will deplete their nutrient supply and become fry. At this point we will introduce them to fish food. Until then, the salmon are heavier than water and live on the bottom of the tank. They prefer a head down and tail up position.
Seeing the alevin exposed on the top of the gravel is an artificial condition unique to small hatcheries like ours. In the wild, conditions are quite different. The spawning salmon prepare a redd, or a nest, in the sandy gravel. The redd is a shallow depression in which the eggs are laid. After fertilization, the female covers her eggs with a swish of her tail. The eggs, and eventually the alevin, remain protected in the redd and are not seen until the alevin are ready to leave the nest and swim for the surface.
December 22 – 570 ATU’s
The alevin are putting on size, well over a centimeter now. Most of our eggs have hatched, and I estimate 300 alevin alive and well. Most prefer to cluster together. The largest group at the opposite end of the tank from the egg basket, the next largest group behind the basket. I wonder if water currents have anything to do with their choice. Whatever their reasons, they aren’t talking. Here is a nice close-up.
And here are Nemo’s friends:
“We wish you a fishie Christmas
We wish you a fishie Christmas
We wish you a fishie Christmas
And a happy New Year!”
The alevin were on their own over the Christmas holiday. As soon as I returned, I headed for school to see how they had fared. Quite well, thank you. Our class had calculated that the alevin would not morph into fry until a week or so after our return, and it appears our calculations were correct. All the eggs had hatched by the time we returned. We lost about 75, but we have at least 300 strong and viable alevin. They are still on bottom but do move about occasionally to explore the tank.
I’ve noticed they don’t like light. They prefer an upright, head down position, as you will see in the pictures below; they cluster that way and wiggle around a lot, especially when in the dark. But if you expose them to light for a prolonged time, they grow still and tend to fall over, or roll over on their back and play dead. The light doesn’t seem to physically harm them but it does appear to make them moody.
We have a fabulous camera that attaches to our computer and allows us to take the photographs that you see on this page. The kids have gotten to be quite the photographers and some of these pictures were made by them.
The alevin average 2.5 cm now, or about 1 inch in length. Their yolk sacs are getting smaller as they use up their nutrients. They are becoming more opaque and taking on dots and other markings. Their fins are becoming more defined, and you can clearly make out their gills working away. Many are aggressive and shove each other out of the way to get what must seem to them a prime location in the tank.
Our tank temperature has held very constant at 5 to 6 degree C. Oh, our tech guy donated a massive backup power supply and we now have our chiller and pump running through it so if we do have a power out the tank will continue to stay cold enough to protect our salmon.
January 9. 680 ATU’s.
We had one deformed alevin that we affectionately named Bubblehead. See the first picture below. He was quite unusual. It appeared as though his egg membrane had fused around his head, or perhaps he simply couldn’t shake it loose. Alevin usually exit the egg head-first, But Bubblehead’s head was clearly encased in the membrane which really appeared to have grown into his body. He also had a most unusual birthmark on his caudal or tail fin. At any rate, Bubblehead could not live forever like an astronaut and he died last night. Farewell, Bubblehead! We rooted for you and we miss you.
Jaws appears in the second picture. Actually, he looks like all his brothers and sisters, so we really aren’t able to identify him in the tank. But you have to admit, Jaws has one mighty mouth!
The yolk sacs continue to shrink toward total absorption and are taking on a silver sheen. The alevin are nearing a very momentous time, emergence, when they will surge to the water’s surface and fill their swim bladders. Emergence is their rite of passage. No longer alevin constrained to bottom life, they will take their place as fry, forevermore “free to move about the cabin.” In the wild this usually happens en mass in the dark of night. I hope it will be dramatic and we will be able to see it happen. Enjoy the pictures!
January 23. ATU’s 760.
Our alevin are nearing the time of emergence into fry, so one last time here are a few pictures of the “babies.” I’m not sure how well the pictures show their continued growth, but as we study them live it is obvious they are now longer and sleeker. Their yolk sacks have shrunk. Their fins are completely formed. Their lateral line, a row of specialized cells that help them to hear sound, is clearly visible running down the length of their bodies. Their bodies have become much more opaque and they have acquired assorted markings in the form of dots and vertical bars on their sides. We have even been able to make out their nostrils. We have also observed their eyes moving in their sockets as they study their surroundings.
January 30. ATU’s 802.
Since the last log entry our salmon have graduated from the alevin stage and have become fry. As alevin, the salmon lived along the bottom, head down and tail up, and depended on their yolk sac for nutrients. Under natural conditions, the salmon actually remain in their rhedd, or “nest,” during this stage, but as the nutrients stored in their yolk sac become depleted they must make a move or perish. In the dark of night, they emerge from their nest and swim to the surface. Somehow they instinctively know this first step means life or death for them. They must breach the surface and swallow air to fill their swim bladders. This organ runs underneath the spine and when full of air it provides buoyancy for the salmon. By adjusting the amount of air in its bladder, a fry can control the depth at which it hovers.
We did not witness our salmon rising to the surface en masse, probably because of their artificial environment. Last week we noted several rising to freely swim about the tank but they always returned to the bottom and lost themselves among their peers. When we returned to school today, though, an obvious and dramatic change had occurred. Most are still near the bottom of the tank, but now they are clearly hovering just above it free swimming in the current.
February 5. ATU’s 842.
I’ll add text to this post later this week. But for now, here is a post-emergence picture. The quickly moving fry have forced us to resort to more traditional photography.
When I arrive in the morning and take the insulating covers off the top and front of our tank, the salmon are hovering just off the bottom of the aquarium. After about 30 minutes they seem to wake up and begin rising into the middle and upper regions. They school and uniformly swim to the left. This surprises me; I thought fish swim into a current and I’m sure the currents in the tank move convectionally and counterclockwise. If I turn off the pump, the current ceases and the fish seem to lose their sense of direction; and turn around in random directions like people coming out of a sleepwalk and lost.
The kids have noticed that their eyes pivot in their sockets as they try to look at you. Their eyes are stunning at this stage, like they are formed from flecks of gold. You can see this in the previous pictures. They are very aware of their surroundings now. They are skittish and start as you approach the tank. The kids are having a great time trying to make them jump.
It has taken more than a week for the masses to recognize their food. It is dark brown, fine grained, freeze dried and smelly. Something like dead fish and I expect that is what it is in part. I keep the bulk of their food in the teacher’s freezer, clearly marked “fish food.” It looks quite like coffee and I’m hoping the coffee drinkers pay attention to my label.
We found one dead fry several days ago. He had been a bit cannibalized. He is only our third casualty since emergence. If you let them set out for a few minutes and then look at them under the microscope their bodies become quite leathery looking and their eyes turn black.
Now that the salmon have reached the fry stage, there isn’t much to be done other than routine maintenance. We feed them twice a day and exchange 5 gallons of water twice a week and it is time to begin vacuuming the gravel bed to remove waste and uneaten food.
With 300 fish in our tank, waste products and uneaten food are a big problem. They produce ammonia which is very toxic to the salmon. Fortunately, bacteria are growing in our gravel bed, the beneficial kind, and they gradually convert ammonia to nitrates and eventually to nitrites. The conversion process lowers the toxicity of the waste products, but in a closed system that isn’t enough. That is why we replace water and vacuum the gravel bed.
Some of our salmon have passed the 3 centimeters mark, but others lag behind. Maybe they hatched later or simply aren’t eating as much. Some are big and fat, others are slim. It has become apparent that the salmon face and swim into the currents, and it appears that you can map the currents and eddies by noting the direction the salmon are facing.
Most of the time the fry move slowly, but occasionally they dart across the tank, and when they do they are lightning fast. There seems to be no explanation for why they do this. The air pump is to our fry as water parks are to kids. They love to swim into its vigorous current until it overpowers them and sweeps them away. But they get right back in line for another go. Here is a parting look at the salmon in the final days of the alevin stage, and two images of our fry that I took this morning.
Our camera has a relatively slow shutter speed and even when the salmon hover they move quickly enough to blur in the pictures. This isn’t necessarily a bad thing; Pollyanna always had something good to say about everything and so will I. I rather like the blur because it shows our fish are active and always moving.
I make my kids write weekly observations about the salmon, looking for new things they haven’t noticed before. If you would like to become an honorary member of the Fort Yukon science classes, start your own observation journal and record what you see in the pictures. Good luck!
Just a short post. Last Monday we noticed that a few of our fry were sick. They were listless, lying on bottom and belly up. At first we thought they were dead, but they weren’t. They would move if we disturbed them. When they attempted to swim, they moved in spirals and they were unable to right themselves.
Temperature is perfect. I’ve checked pH in two different ways. I have a very old water quality test kit that suggests the pH is very low but none of the chemicals seem to be registering color changes, so I don’t trust it. It has probably been in our room for 8 or 10 years. I’ve also used fresh Hyperion pH paper that I purchased this year, and according to it, the pH is between 7 and 8. I believe this is accurate.
We change 15-30 percent of the water every week, which agrees with all the recommendations I can find. We have just begun using a syphon to remove waste from the gravel. We may have started too late, and I suspect a build-up of the waste is the problem. We syphoned a third of the gravel at the first of the week and another third yesterday. I don’t dare do anymore right now. It’s very hard on the ammonia consuming bacteria that live in the gravel.
At first we were removing the sick fish, thinking they might have something contagious. Altogether we have flushed away about twenty. But I no longer think that is the case and we are leaving the remaining disoriented fish in the tank unless they really die.
This is very bad timing. Next week is in-service, and all teachers will be in Fairbanks for the week. Walter, the only person who will remain at the school, will feed the fish and do minor water changes everyday. But there is nothing else we can do.
Below is the most recent picture of the fry. Click on the picture to see a larger, clearer image.
I purchased new testing materials in Fairbanks last week and I’ve tested the water.
pH = 7.6-8 alkalinity = 120 ppm ammonia 3-6 ppm nitrites – good nitrates – good
It’s the ammonia giving us problems. From what I have read, the combination of ammonia and pH at current levels causes stress and slow death. That is exactly what it seems to be doing. There are probably 50 to 80 that are severely stressed at present. We can add ammonia lock and change water. I have vacuumed the gravel over the last two weeks and probably can’t do it again this soon without harming too many of the bacteria. I plan to order a bacteria promoter and more ammo-lock but that will take time. I may have to sacrifice the stressed fry reduce the production of ammonia.
There are signs of improvement in our tank.
pH = 7.6 alkalinity = 120 ppm ammonia = 3 ppm or less nitrites = 0 nitrates = 0
The students have been very concerned about the fry. We reviewed the problem of waste buildup producing ammonia and its byproducts, the role of temperature and pH in governing the ammonia/nitrite/nitrate levels and the severity of risk with each. I then asked the kids what they would recommend we do. They suggested lowering the temperature to slow metabolism, removing all the fish and cleaning the tank, changing water more frequently, treating the water to remove ammonia, siphoning the gravel, and removing the stressed fish. We then considered each suggestion and decided as a group that the best course of action would be to:
- change 5 gallons of water a day (16 percent)
- treat the water to remove ammonia
- permanently remove all stressed fish from the tank
- feed them less
- siphon the gravel again to remove more waste material (next week)
While all the ideas presented by the students had merit, some carried their own risks. Removing all fish and cleaning the tank would have been a terrible strain on the fry, especially given their current condition. I was especially impressed by the student who suggested we lower the temperature because it meant he remembered our lesson on temperature and its effect on metabolism, but we are already at 6 degrees C, about as low as I think we can safely go. And it is too early to siphon the gravel again. We did that very recently. We’ll do that again next week.
Yesterday we removed 138 fry. Today we removed 20 and we may have to remove more tomorrow. This has been hard on the students and at first they felt like murderers. Or at least they thought of me as a murderer, even though I had them do it for me. Yet, they agreed that it had to be done if we are to save our population. Counting the previous salmon fatalities, we estimate our live count now is in the neighborhood of 250.
I believe our initial problem was one of over stocking, too many fish and not enough tank. And I think the tank is stabilizing. The water looks slightly better, the remaining fry look more active, and both the ammonia level and the pH appear to be falling.The changes are slight, but noticeable.
One student noticed that the stressed fish seem to be the smaller ones, and the healthy fry seem to be the larger ones. A good observation!
We have not completely solved the our salmon’s problems, but we have stabilized their environment as best we can with what we have. We are following our plan of action, and chemically the tank is in pretty good condition with two exceptions. The water is extremely hard, and while we have been able to prevent the ammonia level from rising, we cannot get it to drop below 3 ppm. At our current pH of 7.6 -7.8, that is very stressful for the fry. Since the problem began we have lost 356 salmon. About 50 have survived, mostly the biggest and strongest, but everyday we have to remove a few more.
I’m going to Fairbanks today and will pick up more treatment for the tank. I plan to get pH and hardness reducers and more chemical to treat out the ammonia. I’ll pick up a bacteria starter, too, to promote their growth.
The tank looks very lonely these days, but the survivors look strong.
We have overcome! No fish have died in the past week. The water is staying pretty clear and the fish are healthy. I did buy pH and hardness reducers plus a biotreatment to promote the growth of ammonia eating bacteria. I bought a filter pump, too, which is helping to draw out contaminants and floating waste. We are continuing to exchange water and siphon the gravel bed. Later this week I’ll try to take some new pictures.