Aquaponics HQ FAQ

Australian backyard fish farmers are fortunate in that they have a good variety of freshwater fish from which to choose including.

• Barramundi
• Murray Cod
• Silver Perch
• Golden Perch (also known as Callop or Yellowfin Perch)
• Jade Perch (properly known as Barcoo Grunter)
• Honey Perch (properly known as Sooty Grunter)
• Sleepy Cod
• Catfish (several species)

While Rainbow Trout is an introduced species, it can be grown in cooler climates and is a highly prized eating fish.

Freshwater crayfish include Yabbies (Cherax Destructor), Redclaw and Marron.

For information about what fish you are allowed to keep, you should refer to your local fisheries department. The Australian Department of Agriculture, Fisheries and Forestry can also provide information about suitable fish species through their web site www.affa.gov.au.

The best species for you will be determined by a number of factors including:

• Availability of fingerlings or fry.
• Local climatic conditions.
• Government regulations – some species are restricted to particular areas.

Before choosing a species, you should make the effort to eat some fish of that species. It would be counter-productive to spend months rearing a species only to find that you and your family didn’t like the taste.

Fish hatcheries tend to sell fingerlings in minimum quantities of 50 or 100 but it comes down to how many fish you need for your family or friends?

Bearing in mind that about half the weight of a fish will be lost in inedible bits like the head, guts fins, bones and scales, a 500 gram fish is a single adult serve. A couple and two children might need three fish for a meal - 150 fish would enable this family to sit down to a fish dinner each week.

The number of fish that can be kept in a given volume of water will depend on the following:

• The capacity of your bio-filters to convert ammonia to nitrites and then nitrates.
• The capacity of your growing systems to remove the nitrates from the water.
• The amount of dissolved oxygen in your tank.

If your ammonia or nitrite levels exceed a certain point, your fish will die. If you do not have sufficient nitrates to feed your plants they will suffer.

About 3% of the total weight of fish per day is a useful guide. For example, if your fish weigh about 200 grams each, and you have 100 of them, you have about 20kg of fish in your tank. You would then feed 600 grams per day.

While you don’t have to be too precise, if your fish receive too little feed, they’ll take longer to grow out. If they receive too much, it will remain in the water and will contribute to poor water quality. Some species of fish may also develop too much body fat as a consequence of overfeeding.

You can also adjust your feeding schedule to reflect your need for nitrates. If your plants are growing slowly, gradually ramp up your feeding. Initially, this creates more ammonia, then nitrites and eventually more nitrates. You can then reconcile your feeding with the capacity of your plants to absorb the extra nutrients.

It’s best to spread the daily ration across several smaller feeds rather than one large one.

If you see food accumulating on the bottom of your fish tank, stop feeding for a day or two.

Withholding feed for a day every now and then will probably do more good than harm.