Aquaculture from nothing

Question

I'm in the process of setting up an aquaponics (recirculating aquaculture) system. The main fish being raised are Channel Catfish, and in a separate tank I am also attempting to raise Guppies as a primary food source for the catfish.

Catfish, being omnivorous and greedy, will eat almost anything. Right now, they're small (5"-7") and can't fit a guppy in their mouth. I am feeding them on commercial fish pellets but eventually would like to feed them the guppies, grubs such as soldier fly larvae, as well as a small amount of some vegetable matter like duckweed.

The guppies need their own food of course, and I'd like to know what type of food chain I can create that doesn't rely on purchasing or importing feed of any kind. Commercial feeds for fish are typically made from ocean-caught "trash fish" and thus are likely contaminated with mercury or other heavy metals, which is why I'd like to avoid buying feed pellets. It's also expensive.

Several things I've considered for guppy food:

• Daphnia
• Paramecium
• Algae
• Mosquito larvae

Essentially, the only "free" inputs that are available are sunlight and oxygen (air). It seems like, in nature, that is enough to fuel the bottom of the food chain. So what is practical for a DIY system?

Answer 1

Why not simply get a food waste composter with earthworms? This allows worms for fish food, a place to make use of food waste, it gives valuable organic liquid and solid fertilizers that can be used for wheat grass or other edible plants. The water from the fish tanks are used to water the plants, and the plant system is used to filter and clean the fish tank water.
Thus, I wad surprised not to see a plant-based aspect to the fish-based part of the system. Thus, the sustainable aquaponic system is part hydroponic filter. Just my two cents.

Answer 2

Mosquito larvae are easy and reproduce quickly in warm weather. just mix water and a bit of soil and they will come. Guppies are naturally adapted to feed on them. Everything else (apart from algae) will be more laborious and will also depend on water temperature. You could also consider breeding crickets and meal worms indoor if (when) you run out of guppies. Mosquito fish are a pest and basically are guppy and reproduce equally fast. They can be caught in the wild, especially urban waterways.