Friendly Aquaponics

Adding Fish At System Startup

We start all our systems with fish in them. There are “experts” who recommend “fishless cycling”. However, we have never bothered to, simply because starting up with fish works so well There are some pitfalls to avoid, and we discuss them in this section. We call this process “startup”, because you only have to do it once in the lifetime of your system; after that your system just runs; this never needs to be done again. “Cycling” sounds like something you need to do over and over, and you only do this once, so we don’t use that term.

(Below) Some healthy (and we assume happy) tilapia. Like they say: “Happy as a clam before chowder”. You can always substitute koi if you don’t want to eat them, but then you’ll have some MACKER koi to find homes for at some point.

The good news? You can’t prevent your system from starting up. If you do nothing but put a small amount of fish into your system and feed them, the nitrifying bacteria that power your aquaponics system will simply “fall out of the sky” into your system and start replicating until there’s a balanced population. The bad news is that it can take up to three months to complete this “natural” process of system startup. You can start growing vegetables much sooner than that if you “inoculate” your system (search for posts by the tag words “inoculate”, “inoculation bacteria”). Nitrifying bacteria occur naturally throughout our world, so if you put fish in your system and just wait, the bacteria show up and establish themselves within two to three months. This is what the university told us to do; we did it on our first system and it works. It just loses you three productive months during which you may have to make loan payments and eat.

RECOMMENDED AMOUNT OF FISH AND “LOWER END”. We currently recommend operating with 0.3 pounds (three-tenths of a pound) of fish per square foot of raft area in your system (in your fish tank, of course, not in the troughs!). We use trough area as a guide, because the fish are the “fertilizer generator” that feeds the vegetables in the troughs. This is the recommended amount for a mature system, but you don’t need this much to get started. In fact, you don’t even need this much for a “mature” system, as we saw when we visited Patty and Larry Yonashiro of Maui and their 256 square foot “Family” system.

They hadn’t been able to get the “recommended” amount of replacement fish after all their fish died in an accident, and when they’d gone to replace them, they’d only been able to obtain about 7 pounds of 2-inch tilapia fingerlings. This was less than 10% of the recommended 80 pounds of fish this 256-square-foot system “should” have had; yet the vegetables looked incredible: huge, vibrantly healthy, and growing like gangbusters! They only fed these fish 2 times a day because work schedules would not allow them to be home for the “noon meal”, and even so, it all worked fine. This is what we call “the lower end”; or approximately 0.03 pounds of fish per square foot of raft area. Their system worked fine even with only this small amount of fish! These systems are incredibly robust and operate in a balanced manner within a wide range of parameters. The “recommended” amount of fish can go a long distance either way before you get into difficulties.

We recommend starting your system with (at the most) 20% or so of the “recommended” amount of fish for your system. There are a couple of reasons for this: first, it can be difficult or expensive to just buy a large amount (by weight) of live fish, and with our experience with the “lower end” in mind, we know a system that is supposed to have 80 pounds will work just fine with only 8 pounds. The second reason is that during startup you are establishing the nitrifying bacteria population in your system, these bacteria are sensitive to ammonia levels of 3 ppm or over, and an excess of ammonia over 3 ppm can slow down or even stop the startup process in its tracks. Because the fish produce ammonia, a smaller quantity of fish that produces a smaller amount of ammonia is actually desirable during startup. As you will see in a bit, we also recommend not feeding your fish during startup until the ammonia level in your system comes down to 1 ppm, in order to keep ammonia levels low.

DON’T ADD AMMONIA!!! Many of the same “experts” also recommend adding ammonia during startup. This is the “fishless cycling” method that we don’t recommend. The fish you put in your system will add plenty of ammonia the moment they arrive; for they excrete it through their gills while breathing, as well as pee into the pool. They produce all the ammonia you need; adding ammonia only risks overloading the system and slowing down or stopping your startup in its tracks.

Getting Fish Can Be The Hardest Part; Get Some “Gold” Instead!. If finding tilapia, catfish, or bass (whatever you’ve decided to grow) is difficult, expensive, or you just haven’t found a source yet, you can start your system with a handful (or a few more) “feeder goldfish” that you get at Petco. Because goldfish are “ammonia mines”, and you don’t need a LOT of ammonia at first (just enough for your inoculant bacteria to feed on), you only need three or four for a tabletop system; fifteen or twenty for a 64 or 128 square foot Micro System; 40 to 50 for a 256 or 512 square foot Family System, and 100 to 150 or so for any of our “Commercial” systems. The best thing about starting your system with goldfish is that they are inexpensive: feeder goldfish are usually only fifteen to twenty cents each! And if you have trouble getting tilapia or bass, or whatever you’re ultimately planning to use, just leave the goldfish in your system and keep feeding them; they’ll grow fast and provide fish poop for your nitrifiers that is just as good as tilapia or bass poop! We’ve seen goldfish get up to five pounds!

You will want to add additional fish after you’re through startup; but this may give you time to find a source for your tilapia, bass, catfish, or other desired commercial food fish. Note: goldfish will eventually get up to two or three pounds in size; we have never tried to eat them, but they don’t need to be removed from the system later unless you just plain dislike them.

There is one more consideration here: you either filled your system with clean water in the last step, or cleaned it after filling it. If you bring in diseased fish, you’ve got a diseased system that could be difficult to clean up. Getting healthy fish from a known source will give you peace of mind and eliminate costly problems to resolve during startup. This is a good reason to check with your local State fish vet or animal quarantine branch to see what to beware of before buying fish from a local producer.