Your tunnel is the basic housing of your fish farm. This is because in South Africa we are restricted to recirculated aquaculture systems (RAS) owing to our semi arid conditions and of course our temperate climate.
There is quite a bit of structure to your tunnel. Do not be fooled into thinking it is simply just a tunnel – that’s actually the cheapest and easiest part! There is plenty that needs to go into your tunnel for vital aquatic life support before it is suitable to take the ponds for fish production.
Firstly it needs to be big enough. Secondly it needs to house everything needed to successfully grow your fish – which means it needs to provide power to the production systems, as well as fresh water, continuous aeration and easy access. It also needs to provide for removing waste water.
Tunnels are also used to retain heat and to maintain and manage temperature stability within the ponds used for growing fish. When it comes to Tilapia the optimum growing temperature for them is 28C. In South Africa with our temperate climate this can be quite hard to achieve in the cold winter months and your tunnel is one way in ensuring that your fish don’t freeze.
Tunnels come in many shapes and sizes, and of course prices. Fish farms have different requirements to vegetable tunnels and this is primarily addressed by using the correct covering of plastic over your tunnel. We use a multi solar 200 micron plastic that basically allows everything in and gets the air inside the tunnel as hot as possible.
Each of our tunnels has its own electrical supply and meter so that we can measure our power consumption. Each tunnel also has its own fresh makeup water storage reservoir to allow for water changes, filter backwashes etc.
We also strongly urge and encourage you to run an inverter/battery backed up aeration distribution system, preferably two in each of your tunnels that operates independently of the pond systems themselves. In the event of power outage these systems ensure that the ponds will still be provided vital aeration and prevent you from losing fish. To give you an idea in warm water at full loads ponds will start to lose fish in as little as 20 minutes.
On our basic 21 ton per year growout model you will need about 450m^2 under tunnel. Properly kitted out this will set you back around R220k based on what ours cost us. Build it properly and your maintenance costs will be minimal.
To give you an idea the basic structure with the plastic was around R92k. Backup generators, inverters and batteries, air pumps and airlines account for another R33k or so, water reticulation around R31k, electrical reticulation around R26K, peripherals such as nets, feed buckets, test kits etc account for a further R38k. These are our figures based as at June 2015.