Lobster-sized crayfish and fresh produce: A winning combination grown together through aquaponics

It would’ve been a full meal, if only we’d grown beer. As part of a 2015 University of Wisconsin catalyst grant study, I designed and built two fully-automated, semi-flow-through aquaponic systems, raising giant Australian Redclaw crayfish and bell (gypsy sweet hybrid) peppers. This study addressed whether or not produce could be grown on crayfish waste alone as a nutrient source (it could), as well as the animals’ conversion rate of a custom-formulated feed.

The systems each consisted of two 300 gallon circular tanks, a central sump, and two magnetic-drive pumps. Water was pumped from the sump to one of the tanks, housing pre-sprouted pepper plants in five gallon buckets with holes drilled through the sides and filled with lava rocks as grow media. A PVC manifold directed water directly into each bucket, filling the tank about half-way, before it drained into the second tank, housing the Redclaws. Once full, the crayfish tank drained back into the sump, passing through another drilled five gallon bucket, containing additional biological filtration media (“bio-balls”), ultimately creating two locations for nitrogen fixing bacteria colonization (the sump plus the plant grow beds). A slow drip of new freshwater was positioned above the crayfish tank, and a secondary pump connected to a float switch (the same kind you’d find in a toilet tank) pumped excess water out of the sump and into a floor drain periodically, eliminating the need for manual water changes. Metal-halide bulbs were used for vegetative plant growth, and were replaced by high pressure sodium (HPS) bulbs during flowering/pepper production.