Grow Your Own Fish Feed

Plant Chicago intern Charles Cole has been investigating a way to reduce food waste leaving The Plant, while at the same time providing nutrition to the fish in our aquaponic farm. He is doing this through the use of a little six-legged insect called the mealworm. Below is his introduction to the project:

Mealworms for minimizing waste, maximizing food

Aside from energy used for the light and the pump, another primary input into any aquaponic system is the food given to the fish. This is usually in the form of a commercially made dry pellet, a rather unsustainable product due to the significant amount of energy to produce it – and then even more energy to ship it the store – then more energy still for us to bring it to the farm.

The aim of my project is to replace the fish food with a more sustainable alternative that still provides the essential nutrients fish need to thrive. In the past, a research project attempted to feed the waste of another business in the building to the fish, namely the spent grain from the brewery. While this is good edible food for the fish to eat, it is simply one part of a necessarily balanced diet. Imagine eating just bread for every meal all the time!

For my project I am going to add an intermediate step to ‘food waste -> fish feed’ that will allow us to provide a wider variety of essential nutrients. This step is the production of mealworms. The mealworm (Tenebrio molitor) is actually the larval stage of the mealworm beetle, and are a resilient bug that can sustain life on just about anything including coffee chaff, spent grain, spoiled plants from the farm (all waste products found in the building) They can even consume styrofoam! (which would not otherwise not break down for a million years) In turn, these protein-rich little guys can be fed to the fish. Mealworms contain 12 of the 16 elements that are found in living tissues and are rich in vitamins A and B which are essential for proper growth, nutrition, and nervous system maintenance.

Duckweed

A potential supplement to the worms that could be used to diversify the fish’s diet even more is duckweed, which is an incredibly low maintenance plant that grows on the surface of still freshwater. Wild tilapia often consume duckweed for their strong nutrient density wherever it grows and the ones in our system would surely love some as well. Overall, the goal of this project is to extend the idea of a circular economy even further and make even more “waste” in this building a beneficial input into another system.


Note from Eric: The particular variety we are growing is actually a cousin of traditional ‘duckweed’ called Azolla. This genus, which consists of six distinct species, harbors a symbiotic bacteria that is known to be nitrogen fixing – meaning that it can take the nitrogen gas from the atmosphere, and ‘fix’ it into compounds such as nitrate, which is then taken up by the Azolla. So in addition to growing a potential new food source for the fish, we are trying to see if we can potentially have a new route for bringing nitrate to the plants in the farm!

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