Growing Trout in a Bathtub System

Following on from our recent post on Bathtub Aquaponics, Daniel from rural Melbourne posted these great photos of his DIY system on Murray Hallam’s Aquaponics Forum.

Six bathtubs in an Aquaponics system growing heaps of green vegetables

Here Daniel has grouped his bathtubs into an array of six baths that drain into one return pipe that flows clean water thats been filtered by the baths back to the two fish tanks made from IBC shipping containers. The fish waste is growing some excellent Pak Choi (Chinese Greens) that can be used in stir fries for Daniel but any vegetable that grows above ground is ideal for aquaponics.

The bathtubs all empty to one return pipe

Daniel has made his own autosiphons to become the lungs of his system and has built his system along the CHOP method of aquaponics. The only real difference is that his siphons all empty water to one main return pipe that runs off into his shed to where his fish tanks are housed.

Used IBC’s that make up his fish tanks can be found readily on Ebay and usually sell for well under $100 each. IBC’s have a holding capacity of around 1000 litres so are perfect for growing live fish.

Just make sure the IBC you buy has not stored toxic chemicals in it and make sure you store the IBC somewhere away from direct light as they do break down and crack if exposed to sunlight for some lengthy time. Some people wrap insulation around the tank if it’s exposed to sunlight.

Fish also need lots of oxygen so be prepared to buy an aerator from any aquarium shop to adequately keep your fish well supplied with lots of bubbling air.
More people kill their fish from lack of oxygen than anything else. Give them lots of air and they’ll be very happy.

IBC fish tank housed in shed

So how many fish can you stock?

In a one thousand litre container you should stock around 30 fish and grow them to maturity with little problem. Most users do push the number of fish to around 50 with little problem providing you start harvesting your fish on a regular basis and keep the numbers down as they grow past the 300 to 400 gram size.
But putting in 100 fingerlings into this tank is just asking for trouble later as the fish grow to maturity. The water quality and oxygen demand will be too great for the large fish load, so don’t overdo it with your fish numbers at the start.

Keep your system stable

Here Daniel has his two fish tanks housed in a shed which keeps the system stable. It keeps the water temperature stable to a certain degree and keeps the fish happy as they like to swim around in a cool dark environment. Keep your fish stress free and all should go well.
He’s running both rainbow and brown trout in these two fish tanks. Trout are excellent for aquaponics but they do like cold water. Most aquaponics enthusiasts grow trout in Australia over winter.

Daniel with his trout ready to be placed into his aquaponics system

How soon can you harvest your fish?
Trout grow very quickly. The temptation is to keep them growing even larger over the summer months. This is asking for disaster.

Trout will die if the water temperatures rises above 26 – 28 degrees Centigrade and it reaches that temperature quiet easily in the summer months! Trout are a cold water fish.

So what do you do over the summer months? Try another variety like Silver Perch which enjoy warm water and can grow pretty well all year round.

Eggs grown in Aquaponics? Impossible!

So it is possible to grow two sorts of fish species over a one year period and grow lots of fresh vegetables on their waste. With silver perch however, they will grow much more slowly than trout so we can choose whether to eat them when they are small or keep them in the tank over the following season and harvest them when they are a lot bigger.

Aquaponics systems can be cheap to build if you take the trouble to look around demolition sites and used furniture revolve sites now commonly found around garbage dumps.

Daniel says he’s amazed more people just haven’t discovered the power of bathtubs. He’s now looking to expand his system to well over 12 baths and beyond. Thats the great thing about Aquaponics – once you get the madness into you – you don’t want to stop. It just gets bigger and bigger…