Friendly Aquaponics

Feeding The Fish And Making Your Own Fish Food

The fish food we use for both catfish and tilapia is Rangen 1/8” floating catfish food. You can use any floating food that has about a 30% protein, 6% or more fat content, but TRY to find a fish food that comes in the nice small 1/8” pellet size, as we have noticed problems, both with acceptance by the fish when they were fed larger sized pellets, and with the growth rate and health of the aquaponics system. Feed your fish three times daily, morning, noon, and 1 hour or so before dusk. Feed ad libitum, which means as much as they will eat. When you first feed a group of new fish, start feeding a little bit at a time until you are sure how much the fish will eat. Check back in 15 minutes after feeding to see if the feed is all gone, if it isn’t, it means you need to feed them a little less next time. If they eat it all in 5 minutes, you need to feed them a little more next time.

The amount the fish will eat changes as temperatures change throughout the year, and also changes sometimes from day to day for unknown reasons. Just stay in tune as much as you can. Pretty soon you will get used to their feeding amounts and it will be easy to know when to feed them more or less. One additional thing to know is that fish often stop eating for a day or two to two to three weeks after transporting them (a “haul”), and this is not unusual. Just offer them a little bit of food every day and keep an eye on them. When they do start to eat you’ll notice, and then feed them what they will eat.

You’ll notice that the fish get used to being fed and actually will get frisky and jump around in the tank when you arrive with the food. Conversely, if you show up with fifteen people who are on a farm tour (predators!), you may notice that the fish are at the bottom of the tank, and won’t come up to feed no matter how much food you put in.

(Below) This is the fish food we currently use:

IMPORTANT!! Don’t try to save money by using cheap “junk” fish food: This can seriously affect how well your system grows vegetables, and also the health and growth rate of your fish. We first experimented with cheap fish food when we tried feeding some $0.34/pound dog food to our tilapia. This was at a time when the fish food we used 500 pounds a month of had increased in price from $0.42/pound to $0.60/pound. We threw the dog food in the fish tank; it floated, got soft, and the fish ate it. We thought we had found a way to save some money until the next day, when we took a look at the top of the fish tank, and found wads of floating, gritty, yellow fish poop. If you rubbed a wad of the stuff between your fingers it was as gritty as if you had crushed a bunch of corn chips and mixed them with water. It was obvious that not much of the nutritional value of the dog food (if any!) had remained inside the fish. So we canned this experiment early, and the fish rejoiced by eating even more of their “expensive” Rangen 1/8” floating fish food.

Two years later one of our students with a commercial aquaponics system asked me to check it out, and I saw the exact same phenomenon: he had been buying a “cheap” large-pellet-size, gritty fish food that left gritty fish poops on top of the tank water. The plants didn’t quite seem right. They were not exactly sick or obviously suffering from a nitrogen deficiency, but they didn’t seem to be doing well, which is the way plants in an aquaponics system normally look.

I lifted a raft, and in contrast to the normal light-colored or white roots I expected to see, I found darkish-colored roots with a light coating of slime. Apparently the fish poop, instead of breaking down into the fine particles ours does, had floated out into the troughs and deposited onto the plant roots to finish the process of decomposition there. I recommended switching fish foods to the “expensive” food (that breaks down inside the fish and inside the fish tank into fine particles). Within a couple of weeks, the plants’ roots had cleaned up, they all looked much more vigorous and like what we had come to expect from the systems on our farm, where we use the “expensive” fish food.

(Below) Sick slimy roots result from feeding a non digestible fish food, and NOT from slimy fish poop!

This phenomenon also happened in a different location with a student who was using the first organically certified fish food: his roots got clogged and slimy, because the food (although organic fish food, which is not required for organic certification of your aquaponics systems!) was not being thoroughly digested by the fish. It was a bad fish food, because it was coming out the other end of the fish in such large chunks the bacteria couldn’t get to work on it, and it just clogged the plant roots, with the result we just described. The worst thing about this was that this food cost three times as much as the Rangen fish food we use.

The moral is: cheap is often too expensive to use! (And if you read the last paragraph, you will also realize that sometimes expensive is even more expensive to use!). The same reasoning applies to blowers, water pumps, and other equipment. Aquatic Eco Systems gives a great example of a “cheap” $259 water pump in their catalog that only uses $813 more of electricity per year than the “expensive” $479 water pump. So, be on the lookout for ways to do things more economically and more easily, but also try to see everything that is affected by your choice to make sure that your choice isn’t actually costing you more in the long run.

MAKING YOUR OWN FISH FOOD During every training someone asks “what about making your own fish food?”. One of our students grows duckweed and black soldier fly larvae, dries them, and then grinds them in a home coffee grinder to make a floating fish food that her fish love. We estimate that if her labor is worth $10/hour, her fish food costs her about $12/pound when finished. This is because she only makes a small amount of food at a time. If she made a larger amount of food using slightly larger equipment, the amount of labor required to produce the food, per pound of finished food, would decrease. This is called “economy of scale”.

Making fish food on this scale is fine for a backyard aquaponicist with a hobby system, but if you are operating a commercial aquaponics farm it is impossible to support. In order to make your own fish food economically and sustainably, you have to do it on a scale that allows you to afford to “buy your own fish food”. If commercial food is $1/lb., your fish food needs to cost you LESS than that; or at least only slightly more than that, or it’s not sensible to pursue.

Black Soldier Fly Larvae

Good things about feeding your fish BSFL:

1. Cheap
2. Provides the ability to bio-degrade animal corpses and plant matter into fish food.
3. High in protein and fat.

Potential drawbacks to feeding your fish BSFL:

1. BSF larvae sink when put into the fish tank; this makes them less than the optimum food for fish like tilapia, which are hard-wired to eat floating food. Good for catfish, though.
2. The possibility of contamination of the BSFL with fecal coliforms, salmonella, shigella, and other potentially lethal bacteria through a number of avenues. I’ll explain a bit:

The real problem is that there’s so much at stake when you’re dealing with these pathogens; it’s not just a little stomach upset. If a few of your customers get a dose of the wrong e. coli from your vegetables, you’re talking about possible deaths, kidney failures, and other complications. I couldn’t live with the responsibility for this on my plate; how about you? Are you willing to risk it because you’re sure you’re right?

And for all you “compost is safe to use in aquaponics fans”, and “BSF is safe to use in aquaponics fans” your compost and your BSFL growing operating is safe, except for the rat that ran over it in the middle of the night and peed and pooped on it; and the flies that land on it in the daytime that were just laying their eggs on a dead animal carcass or bit of excrement a moment before; and the bird that lands on top of it and poops just before it flies away.

As a result of these things that happen in the real world, any contention that compost or BSFL is safe to use in aquaponics systems is simply not a scientifically supportable one. Unless you have your compost or BSFL growing unit in a sealed container that rats, birds, and flies CANNOT possibly visit, and you sterilize it before putting it in there, and sterilize any future inputs before adding them, then your compost and BSFL are exposed to all these sources of contamination.

And more: having had both interns and employees, I must add: “and except for the employee that disposes of the stable muck there, then covers it with grass to hide it, because it is less work than taking the stable muck all the way to its designated safe location”. Insisting your compost and BSFL are safe for your aquaponics is akin to insisting that Santa Claus really does exist.

So, you need to make your own decision on this; however as authorities that people look up to and take advice from, Susanne and I can never endorse something like this that MIGHT cause someone to die someday.

And as Dirty Harry once said: “Feeling lucky, punk?” (no personal inference here, just a cosmic comment on how people can manage to magically feel immune from consequences). Are you feeling lucky?