FARMING

Understanding Recirculating Aquaculture Systems

Culture Tanks
Culture tanks range in sizes and shapes and are made with many types of materials. Tanks should be inexpensive, durable, easy to manage during production (i.e., accessible, easy to harvest, have proper drains), allow flexible use and made of non-toxic materials. Vynil pools should be food grade and not black on the bottom so you can see your fish. They all have different cost structures and usually specie will dictate system.

Aquaria are a practical method of introducing aquaculture. For maintaining small and more exotic aquatic species, commercially available aquaria are adequate and reasonably priced. Aquaria are suitable for spawning, hatching and growing many fish species.

For the culture of larger "food fish" species, round tanks are nice. A circular water flow can be maintained in round tanks that makes cleaning easier (solids will move to the center of the tank), water quality will be uniform throughout the tank and the fish will metabolize food better due to constant "exercise." Square or rectangular tanks are also used for larger fish and are, generally, easier to construct, take up less space and are easier to harvest. These tanks, however, may need to be cleaned more often as solids (i.e., faeces and uneaten food) tend to collect in areas where water flow is inadequate.

Tanks can be purchased directly from pet stores, aquaculture suppliers or can be improvised from material that can be found locally. It is important to remember that water used to culture aquatic organisms should only come in contact with materials that are "food grade" quality (i.e., suitable for storage of food products) and that will not leach products that are toxic to the organisms being raised or the consumers of those organisms. A few examples of materials that can be used are:

glass, or acrylic plastic - Used to construct aquaria.

fiberglass - Tanks are easy to build, modify and repair; pre-fabricated tanks can be purchased in a large range of sizes and shapes and is extremely expensive.

Treated plywood, cement blocks or galvanized steel - Tanks are easy to construct and can be a cheap alternative; cover with a non-toxic liner material (do not use liners treated with fungicide e.g., pool liners) or paint with water proof epoxy paint.

Epoxy coated steel - Expensive.

Poured cement (e.g. casket liners, old septic tanks) - Potential to find some good bargains, but tough to move.

Polytanks or roto moulded tanks are practical and easy to engineer but no manufacturer builds large tanks for the aquaculture industry..

Plain bricks and cement can more often than not be the most cost effective solution but at BREAM we are now manufacturing PVC tanks

Systems design

Speak to 5 different sytems specialists and you will get five different designs. I have yet to find agreement on any one system. Materials are also a huge debate but I have found PVC the most cost effective and reliable material to make ponds. It is easily changed and modified as your ideas improve your system which tend to happen from time to time. I have moved away from the classic D-End raceway and move to a modified version which basically has a single channel and a long narrow return channel for the Bio-Filter and of course round tanks.

Cost of a System

A small commercial facilty would be a minimum of 60 tons annually. The installation of this facility would cost in the region of R500 000.00. One would need at least two tunnels (10X30m) with a level and smooth sand floor. This would be one's single largest cost of course not including cost of land, we presume one also owns land. Location is important as one does want to have as much solar exposure as possible. Water use will require that you replace at least 10% of total volume of water in the system once a week. There is adequate processing facilities all around South Africa so one does not have to build a processing plant. We are at present building a new commercial hatchery to supply fingerlings throughout South Africa. How much can one earn for 1KG of tilapia, well thats depends on your market, supply and demand largely dictate but if one can raise 1 kg of tilapia for under R10 rand you will be in good shape. Food is around R4500 per ton and you need to feed 2-3% of biomass every day. FCR (feed conversion ratio) for fish is between 1:1 to 1:1.5 (this means you need to feed 1kg of food to grow one kilogram of fish - Chickens require around 3 kilograms to grow lkg and beef need 7kg to grow 1kg). Materials suitable for fish ponds is of course PVC.

How many fish can one grow in 1000lt of water - 50kg's.