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Fish Stocking

Every system is different and peoples environmental conditions can vary quite a lot, but there has to be some form guideline as to what will work well for the majority of people. We recommend stocking around 20-25 fish for every 500L of growbed media in your system, this is assuming you have growbeds that are around 25-30cm deep.

Ultimately the amount of fish you can safely keep in your system depends on many factors, feed rates, water flows, oxygen levels, number of plants, pumping rates, fish species and water temperature, to name a few of the major factors. So, let’s say perhaps that you are looking at making a very simple system like the example system we have built in this manual, made from the one IBC cut into two pieces to make the growbed and fish tank. This growbed has 250L of media in it, perfect for around 10-12 fish. This is allowing for them to grow from fingerling up to a plate size of around 400-500g. If you double the growbed by adding another one the same, then you can pretty much double the amount of fish you have to 20-25 fish in the system.

This 8 bed aquaponic system with about 4000L of media and a 5000L fish tank, was running on only 70 fish when this picture was taken. That’s less than 9 fish per 500L of growbed media.[/caption]

We’ve found with experimenting that you can grow a lot of plants with only a fairly lightly stocked system, and a lightly stocked system is more resilient if things happen to go wrong. Getting my fish home. You should speak to your fish supplier first, fish transporting can often depend on the size of the fish and the distance you are travelling with them, or the amount of time they will be spending in transport. Often suppliers will bag small fingerlings in clear plastic bags with oxygen added to the bag, this can allow them to be transported for long periods of time with only a slight chance of losses. Sometimes you may be required to take an esky or similar to the fish supplier, this is good so long as you take along a battery aerator with you to supply them with air for the trip.

Feeding Your Fish

We recommend that you use a quality aquaculture pellet to feed your fish, you can supplement this with alternate feeds like worms, maggots, black soldier fly larvae and plenty of other different types of alternative feed, however it’s always good to have the basis of a pellet feed there as an essential component of the fish diet. People often ask about keeping a system completely closed loop, producing all the feed you need within the system and from system rubbish and scraps. This works to a minor extent, however you must have external input into the system if you are removing nutrient from the system in the form of food to eat.

So how much do you feed your fish? Basically, as much as they want. If your system is mature then we recommend that you feed your fish as much as they want to eat within a few minutes. Any uneaten food should be removed from the system before it sinks and rots consuming oxygen from the water while increasing ammonia levels.

I Want More Fish in my System

If you want to produce more fish in your system but can’t increase the size of your growbed area then finding a way of removing solids from the system will help lower the nutrient levels. This is a fairly hotly debated area of aquaponics and really it’s up to the individual and what they want from their system. Installing some form of solids removal like a swirl separator or settling tank allows you to remove the majority of large particulates (uneaten food and fish manure) before they go into the growbed. You will however have to regularly empty these solids and dispose of them in some way, preferable into a worm farm or into your garden. Personally we prefer to leave the solids within the system, it simplifies the system while still allowing reasonable levels of fish production, and ensuring that your often expensive fish feed is put to good use, growing the plants in your system.