“So, you have the plants on top and the fish underneath?”
It’s a common enough question as folks try to wrap their heads around how our aquaponics greenhouse works. Maybe, in a tiny schoolroom-style situation with goldfish, such a layout 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 2011-12, the four large fish tanks fed two long raft beds, which float the plants on top of the water so their roots can gather nutrients below as it flows past. An array of NFT (nutrient film technology) channels near the south end of the greenhouse provided another method of growing crop — especially plants with a shallower root system.
As our operation matured and demand for fresh, clean, year-round greens increased, we’ve added significantly to this original setup, including two arrays of NFT systems that sit above the rafts, stacking our growing potential. Lush greenery was now abundant!
And then, one spring, the biggest tilapia in one of the tanks got frisky, and as we were pulling them out for harvest, one momma gave a great gulp and threw her young all over us and onto the floor and back into the tank! Tilapia are mouth brooders to keep the eggs and small fry safe from the other fish, and now there were literally thousands of tiny tilapia everywhere! We scrambled to scoop up and save what we could into a little aquarium we use as a NICU nursery, but some of them found their way through the system and into the rafts.
At first, we didn’t notice, but as the little fish grew bigger, we saw that the lettuce in the raft system looked stunted and unhappy. Pulling up the rafts, we could see that their roots were completely chewed off! The little fish were now growing big enough to eat up those roots, causing significant damage. It was time to catch the beasties!
And we tried all sorts of ways to catch them, but eventually we moved all of our lettuce production up into the NFT system (where the fish could not reach them) and kept kale, kohlrabi and Swiss chard in the rafts, which didn’t appear to be as appetizing to the fish. A few starved out, and we caught some more, so we thought we were doing well.
Then, this last winter, even the kale and the Swiss chard roots were suffering. No more playing around — it was time to settle this problem. We hatched a plan and gathered our materials.
This coordinated well with a major replanting that meant we were emptying an entire raft’s worth to replant with new crop. Because of this, we could remove all the floating rafts from one bed at a time without worrying that plants would dry out and suffer. Using a pressure washer, we flushed the pipes leading into and out of the beds, sealing them off with a wire mesh, as well as the pipe that runs between the two. If there were fish, they would now be isolated in the beds with nowhere to hide.
“Can you see any?” Mom asked as I came into help. The backs of tilapia are dark, and a thin layer of silt on the bottom of the tank offered camouflage. “There!” I cried, as I saw five medium-small sized fish mingling by an outlet hose, hoping they could hide. They weren’t very big, but we were going to catch them.
We’d fashioned a wide net with a PVC-coated chain stitched into a pocket along the bottom. Mom stood on one end of the raft and I was on the other as we laid the net across the width of the bed, reaching down with our arms to make sure there were no escape routes along the sides. Slowly, slowly, we dragged the net from one end of the raft down to the other, until we had the fish cornered, and Steve could net them out. A few drags back and forth and we had all five — one raft down, one to go!
We moved the rafts with plants on them over from the one bed to the other, exposing the second bed. Dropping in the weighted net as before, we started marching our way across when like a comet one huge fish flew up into the air and over the top of our net! What? That must be the root eater! Look how big its mouth is!
Back and forth we went with the net, squealing as the large fish kept leaping over the top. We’d caught all the little fish and just had this last one left to nab. Mom and I made a dash for it with the net, reaching the other side and quickly flipping the top over the edge so the fish was completely concealed and couldn’t leap out (though it tried several times). Finally, Steve was able to nab it in the net, and we set it outside in the snowbank like ice fishermen do. We were all soaked but laughing and celebrating our fish-catching success.
That big tilapia sure tasted good baked for dinner that night!
Our catching festival cured the root eating, and now we have a host of lettuce growing in the raft beds as well as much happier Swiss chard plants. If any munching tilapia come back, we now have an action plan!
It’s time to harvest some delicious lettuce for this week’s CSA shares. (Interested in our Summer CSA program? Visit www.northstarhomestead.com/NSHF/product-category/csashares/) See you down on the farm sometime.
Laura Berlage is a co-owner of North Star Homestead Farms, LLC and Farmstead Creamery & Café. She can be reached at 715-462-3453 or www.northstarhomestead.com.