“So you have the plants on top and the fish below?”
This is quite a common question as people try to figure out how our aquaponic greenhouse works. Perhaps, in a small classroom-style situation with goldfish, such an arrangement might work – but not with tilapia. This year has been a living example of why on our farm.
When we originally installed our Nelson and Pade aquaponics system in 2011-2012, the four large aquariums fed two long raft beds, which float the plants above the water so their roots can pick up nutrients from below at the as they pass. A network of NFT (Nutrient Film Technology) channels near the southern end of the greenhouse provided an alternate method of growing, especially plants with a shallower root system.
As our operation has matured and the demand for fresh, clean greens year-round has increased, we have added significantly to this original setup, including two sets of NFT systems that are located above the rafts, piling up our growing potential. Lush greenery was now plentiful!
And then one spring, the biggest tilapia in one of the tanks got frisky, and as we were taking them out for harvesting, a mama took a big gulp and threw her little ones on us and on the ground and in The reservoir.
Tilapias are mouth brooders to keep eggs and small fry safe from other fish, and now there were literally thousands of tiny tilapias everywhere. We scrambled to collect and keep what we could in a small aquarium we use as a NICU nursery, but some of them made their way through the system and into the rafts.
At first we didn’t notice it, but as the little fish got bigger, we saw that the lettuce in the raft system looked stunted and unhappy. Going up the rafts, we could see that their roots were completely chewed up! Small fish were now getting big enough to eat those roots, causing significant damage. It was time to catch the critters.
And we tried all kinds of ways to catch them, but in the end we moved all our lettuce production to the NFT system (where the fish couldn’t reach them) and kept the kale, kohlrabi and chard carding in the rafts, which was not the case. seem to be equally appetizing for fish. A few succumbed and we caught some more so we thought we were fine.
Then, this winter, even kale and Swiss chard roots suffered. No need to play anymore, it was time to fix this problem. We made a plan and gathered our materials.
This coordinated well with a major replant which meant we were draining an entire raft’s worth to replant with a new crop. Because of this, we were able to remove all of the floating rafts from a bed at once without worrying that the plants would dry out and suffer. Using a pressure washer, we flushed the beds inlet and outlet pipes, sealing them with wire mesh, as well as the pipe that connects the two. If there were any fish they would now be isolated in the beds with nowhere to hide.
“Can you see any? Mom asked as I walked in to help her. The backs of the tilapias are dark and a thin layer of silt on the bottom of the tank provided camouflage.
“The!” I cried when I saw five medium to small fish mingling near a drainpipe, hoping they could hide. They weren’t very big, but we were going to catch them.
We fashioned a wide net with PVC coated chain sewn into a pocket along the bottom. Mum stood at one end of the raft and I was at the other as we laid the net across the width of the bed, reaching out to make sure there were no escape routes along sides. Slowly, slowly, we dragged the net from one end of the raft to the other, until we had the fish stuck and Steve could get them out. A few drags back and forth and we had all five of us – one raft down, one to go!
We moved the rafts with plants on them from one bed to another, exposing the second bed. Dropping the weighted net as before, we started to cross when, like a comet, a huge fish flew through the air and over our net! What? Must be the root eater. . . look how big his mouth is!
We were back and forth with the net, screaming as the big fish kept jumping over it. We had caught all the small fish and there was only this last one left to catch. Mom and I rushed over it with the net, reaching the other side and quickly flipping the top over the edge so the fish was completely hidden and couldn’t jump out (though he tried several times). Eventually Steve managed to catch him in the net, and we put him outside in the snow bank, like ice fishermen do. We were all soaked but laughing and celebrating our fishing success.
This big tilapia was really good cooked for dinner that night.
Our Capture Festival cured root eating, and now we have loads of lettuce growing in the raft beds as well as much happier Swiss chard plants. If a nibbling tilapia returns, we now have a plan of action.
It’s time to harvest some delicious lettuce for this week’s member shares. See you soon at the farm.
Laura Berlage is co-owner of North Star Homestead Farms, LLC and Farmstead Creamery & Café. (715) 462-3453 www.northstarhomestead.com