Intensive Culture of Tilapia in Tanks I. Grow-out Culture- Tank Design & Operations)

Many are interested in the culture of Tilapia in tanks because of the advantages it offers: first,  less space is needed, second,  better management control, third, less labor is needed, fourth, better quality of fish produced, and fifth, less risk of loss of stocks due to typhoons and flooding.

Its only disadvantage is- it is more expensive to construct and because no natural food can be produced, feeding will depend entirely on commercial feeds.  Encouraged by these reasons, many have actually ventured into this business but failed because of lack of information on the system requirements.  The design of the tank system together with the life support system is crucial to the operations and will determine the success or failure of this business.

 

TANK DESIGN

Two shapes of tanks maybe used, one is the circular tank and the other is a rectangular/square tank. Whatever the shape is chosen, the ideal size may range from 10 to 200 m³.  A square or rectangular tank is recommended because they save space and are cheaper to construct  because they can share walls.  The bottom of the tank is tapered by 5^o towards the drain so that the wastes are easily collected. This eases up the removal of waste by simply removing the drain stand-pipe. 

The tank is plastered with "Sahara" waterproofing additive to prevent seepage in the tank.  It is not necessary to paint the tank.

Aeration

There are several kinds of aerators available in the market.  However, only these two are recommended for efficiency in increasing the oxygen level in the water and power consumption.  The Roots-type Blower is a hi volume/ hi- pressure aerator that is suitable for large operations (e.g. several 100m³ tanks) and if the water level in the tank is more than 1.0 m.   For  smaller operations , i.e., 1 or two tanks with a water level of only 1 meter,  a Vortex or Ring Blower which is a hi-volume/ lo-pressure maybe sufficient.

Water Supply and Drainage System

Since tank culture uses a lot of water, adequate supply of good quality water should be available. The amount of water required will depend on the extent of the operation.  A shallow well (10-80 ft deep) is suitable because it takes less power to draw out the water.  Otherwise, irrigation water or from the tap can be used.

Chlorine in tap water can be neutralized by aerating them at least overnight or with the addition of 6 g of sodium thiosulphate per ton of water.

Tank Preparation

Unlike in other aquaculture systems where  elaborate preparation is needed, the tank is  prepared by simply scrubbing the walls and filling it up with water. It is then ready for use and maybe stocked with fingerlings immediately. Stocking of fingerlings into the tank uses the same method as in any other culture system. Acclimation of fingerlings for at least 20-30 minutes before directly putting them into the tank is very important.

The stocking density is between 100-180/m³. The high stocking density is needed in order to make the production system cost effective. 

To compute for the projected harvest, an assumption of 150/m³ stocking density, a tank size of 50 m³, a recovery rate of 80% and an average harvest size of 250g will produce about 1,500 kg of fish at harvest.

Feeds and Feeding

There are two types of commercial feeds available in the market, the sinking feed and the floating feed. The later is preferred because it allows better monitoring of the amount of feed given.

The feed can be broadcasted directly to the fish. The feeding rate is usually 1.5-2% of the body weight. This however is just a guide. The amount of feeds given may decrease or increase depending on the appetite of the fish.  As a general rule, if the fish cannot consume all the feeds given within 5 minutes, then it is overfed and the amount to be given in the next ration should be reduced.

The size of the fish should be monitored every week in order to adjust the amount of feed given. In order to get a very realistic feeding rate, the number of mortalities should be noted daily.

(See article on feeding management in “Reducing Feed Cost in the Culture of Pangasius article)

Water Management

Feed composition, fish metabolic rate and quantity of wasted feed have major detrimental impacts on tank water quality. As pelletized feeds are introduced into the culture system,  it is either consumed by the fish or left to decompose in the system. The by-products of fish metabolism include carbon dioxide, ammonia nitrogen, and fecal solids. If uneaten feeds and metabolic by-products are left within the culture system, they will generate additional carbon dioxide and ammonia nitrogen, reduce the oxygen content of the water and have a direct impact on the health of tilapia.

To maintain good water quality, water exchange will be necessary.  A 20-30% water change may be done every week during the first month of operation.  A bigger volume and more frequent water exchange maybe necessary as the fish becomes bigger.  This is because they eat more and defecate more.   

The re-circulating system for water re-use is advisable if water is scarce or expensive.  In which case, a filtration system will have to be included in the system.   

Harvesting

Harvesting in a tank system is simple and requires less labor. The tank is simply drained until the water level is enough to submerge the fish. Fish may then be scooped-out.   When a small number of fish are left, the water can be drained totally and the fish are picked-up.