Feeding The Fish/Making Your Own Fish Food
The fish food we use 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. This is the fish food we currently use:
Watch out for 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 darkishcolored 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.
Sick slimy roots result
from feeding a non
digestible fish food, and
NOT from slimy fish
poop! The answer? Get a
fish food that your fish
are eager to eat, AND
that comes out of their
“exhaust end” in a
completely slimy form.
The system bacteria can
break down this “slimy”
fish exhaust efficiently
and thoroughly, and you
will avoid this problem!
This phenomenon also happened 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. Also see the section Fish Food/Animal Food Manufacturing
Plant for more information about what it takes to make your own fish food affordably.
Observe your fish. Are they frisky? Are they morose? Feeding well? On the bottom? Swimming all around?
Reading trashy magazines? Floating upside down is a bad sign, for sure. Observe your water. Is it getting
darker or lighter? Staying the same? More crud (technical term) or less crud in the troughs and tanks? Check
screens in the tanks and clean when necessary, as when they get clogged the tanks will overflow onto the
ground.
Tilapia are generally robust. We haven't had any disease events in seven years, and I don't know of an
aquaponics operator on the Big Island who has. Every once in a while we get one dead fish. If you get more
than one at a time, or you get one over several successive days, you may have a problem and should do
something about it. If you’re in Hawaii, call us, or call Dr. Allen Riggs, the State Aquaculture Veterinarian,
(808-832-5005). He is a great resource for biosecurity and fish disease problems. Biosecurity is when you
have systems and procedures in place on your farm that protect your fish from disease, even when it may be
on other farms around you. If you're not in Hawaii, call your local University aquaculture extension agent, or
an aquaculturist nearby.
You can EASILY kill fish by leaving the cover off the tank or open. They are crowded enough that some
will go exploring, the way tilapia are known to do. You find them on the ground the next morning. It seems to
be the largest and most marketable fish that do the exploring, so this can be expensive. Designing your tanks
to keep the water level about 6" below the top helps; so do nets around the sides (also keeps herons out, if
you have those in your area).