A Community and Forum For Aquaponic Gardeners

Amount of fish in my beginners' system

I'll be starting up my first aquaponic system this spring. I have 10 tilapia currently in an ordinary aquarium indoors. They are 10-15 cm now (4-6 inches). My planned AP system will have a 300 litres fish tank (66 gallons), and a grow bed that is approximately 2 metres x 60 cm x 27 cm. That adds up to 300 litres of media, so, the same as water volume in the fish tank.

I checked the measurements against the "rules of thumb" here, and they seem to be ok.

But how many fish would you recommend in that volume? I have one recommendation from a swedish aquapon who is more used to cold water fish, and he suggests 6-8 fish in that, but I have seen much larger amounts suggested.

What would you suggest? Do I need to buy more tilapia, or will it be ok with the 10 I have?

If 10 fish do not provide enough fertilizer, would it be an option to top it up with pee, until my fish have multiplied themselves? It isn't all that easy to get hold of tilapia in Sweden.

Louise

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Permalink Reply by TCLynx on February 21, 2012 at 4:38pm

Bob,

Sometimes you can get away with not having additional aeration beyond just the water splashing back from the grow beds, however, sometimes that is not enough.

It will depend on your system design, system size, type of fish, amount of fish, climate, temperatures, and pumping schedule.

My 300 gallon system, last year, I let it run with only the water falling back into the tank from the grow beds. It ran fine and the fish did well until it got warm and sometime in April or May when the weather got warm enough that the water was staying over 80 F even overnight, the fish quit eating very well. When I added the air pump and air stone back in, the fish went back to eating well and all was good again.

Some types of fish can survive lower oxygen levels than others but most fish do better when the dissolved oxygen levels are high.

Now having some redundancy like putting an air pump on a battery backup is also a way to buy some extra time in case of power out or breaker on the pump circuit tripping.