We made a decision this past fall to change our aquaponics system over from tilapia to rainbow trout. The logic seemed simple and sound. Going into winter it is more expensive and challenging to keep a system warm. Rainbow trout don’t care if it’s warm. In fact they flat out don’t like it warm. They love 50 deg F water, and when it get's to 70 deg F. they don’t do well. Tilapia are on the other end of the spectrum. They only like it warm. 80-85 deg F is their sweet spot. Below 70 deg F they start to shut down, get listless. So the thinking was if we use the trout, we don’t have to heat our water, which makes the system operation much less expensive.

We found a small farm selling 8-10 inch trout for a good price. We went over and loaded 100 rainbow trout into barrels. Then the fun began. We stopped 30 minutes down the road and discovered one of our air lines had come apart and was not in the water. The other was not spitting much air into the barrel. The fish were not looking very happy. We messed with lines, ended up buying more air stones and an additional air pump. But we had some sad looking fish.

By the time we made the 3 hour drive home, half our fish had died. The shock of going airless at the beginning was simply too much. We installed the living fish in our system and all seemed well for about a week. Then we started having fish die - one or two a day. We checked our water and everything seemed good. They were dying but we couldn’t see anything wrong with them. Finally we noticed the fish had white, inflamed gills. They had little if any blood going through their gills, so they were dying of hypoxia – lack of oxygen, because their gills couldn’t get the oxygen out of the water. It turns out they had picked up some sort of bacterial infection – maybe they had it from the farm, the travel, we don’t know. But treatment was simple. Add a small amount of salt to the system (5 parts per million). It doesn’t affect the fish or plants, but kills the bacteria. It worked and our fish got healthy.

Then we discovered another issue. The fish were healthy and happy, but the plants still wanted to be warmed. Sure we could grow some kale, certain lettuce and spinach crops - sort of. But without heat, it simply wasn’t warm enough in our climate to keep plant growing well. The moral of the story… Sometimes saving money doesn’t. The amount we spent swapping over to the trout and then having it be an unsuccessful experiment was discouraging.  But school can be expensive. We just ended up revamping the heating system to be more efficient, added a trapped air layer to the greenhouse to increase efficiency, and re introduced tilapia back into the system. And truth be told I like the tilapia.

What can you learn from our saga? Think through all the ramifications of changes you make. They are probably more far reaching than you realize. Read and ask questions. Be willing to learn from others. It’s a lot cheaper. Be careful to think about your system objectives, what you want to produce, and the environmental inputs into that system that will affect your growing abilities. And if you try something and it fails, don’t give up. Back up, re-evaluate, adjust, and try again.

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