Cages Tilapia fish farming


Growing fish in Cages system

By Uri Ben Israel an Aquaculture expert
Raising fish in cages is a successful system used in many parts of the world.  It has replaced the traditional fish-growing method of earth ponds.  Its advantages are well recognized and it is widely spread all over the globe.  The first and most important advantage is the unlimited amount of water surrounding the cages.  This unlimited water supply provides vast amounts of oxygen and running water which is necessary for productive fish farming.  Secondly, the financial investment in such a system is much lower.  This system of cages is simpler in daily operation in comparison to any other commonly used method of growing fish.

 

Site Selection and Placement of Cages

Large bodies of water tend to be better suited for cage culture than small ponds, because the water quality is generally more stable and less affected by fish waste. Exceptions are entropic waters rich in nutrients and organic matter. Small (1 to 5 acres) ponds can be used for cage culture, but provisions for water exchange or emergency aeration may be required. Cages should be placed where water currents are greatest, usually to the windward side. Calm, stagnant areas should be avoided. However, areas with rough water and strong currents also present problems. 

Cages may be moored individually or linked in groups to piers, rafts, or lines of heavy rope suspended across the water surface. At least 5 meters should separate each cage to optimize water quality. The cage floor should be a minimum of 4 meters above the bottom substrate, where waste accumulates and oxygen levels may be depressed. However, greater depths promote rapid growth and reduce the possibility of parasitism and disease.

 

Grow-Out

The optimum fingerling size for stocking in final grow out cages is determined by the length of the growing season and the desired market size. The shorter the growing season, the larger the fingerlings must be at stocking. The use of male populations, which grow at 30-40% the rate of female populations, will result in larger fish, greater production and a reduction during the grow-out period.

Recommended stocking rate of tilapia fingerlings depends on cage volume, desired harvest size and production level, and the length of the culture period.

 

Water exchange is less frequent in large cages, and therefore the stocking rate must be reduced accordingly to fish size.

In tropical or sub-tropical regions with a year-round growing season, a staggered production system could be used to facilitate marketing by ensuring regular harvests, e.g., weekly, biweekly, or monthly. The exact strategy will depend on the number of cages available and the total production potential of the body of water.

 

Harvesting fish

Total production


Total production in cages increases as the stocking rate is increased. However, there is a density at which tilapia become too crowded and water quality within the cage deteriorates to a point that causes a decline in growth rates.  In cages, production should be limited to 30 -50 kg per cubic meter. Tilapia continues to grow above these levels at gradually decreasing rates, but they convert feed poorly, and the risk of loss due to oxygen depletion or disease is greater. For maximum turnover of marketable fish, it is best to limit production to levels that do not depress growth.
The total number of cages that can be deployed in a lake and therefore total fish production, is primarily a function of maximum allowable feeding rate for all cages in that body of water. The total feed input is related to number and size of fish in the cages (the biomass) and is limited by surface area of the pond.

 

Cages advantages and disadvantages

Some advantages are:

·       Flexibility of management

·       Ease and low cost of harvesting

·       Close observation of fish feeding response and health

·       Ease and economical treatment of parasites and diseases

·       Relatively low capital investment compared to ponds and raceways

Some disadvantages are:

 ·         Risk of loss from poaching or damage to cages from predators or storms

·         Less tolerance of fish to poor water quality

·         Dependence on nutritionally-complete diets

Leveling turned over – This may occur when anaerobic material flows up from the bottom of the lake, increasing toxic chemicals and lost of oxygen in the water. 


The Cage


1. The cage has three main parts. The outer part which floats on the water surface is made from 2-3 HDPE tubes. The diameter of the tubes is 250mm and they compose the upper floating base (as seen in the pictures) to which the fish growing net is tied.














Cage Net2.   The second component is the net, where the fish are kept and grown. The net is completely submerged under water in a depth as determined by the farm's requirements.     








Mooring Anchor3.   The third component is the mooring system located at the bottom of the lake which anchors the cage system to the designated location above water surface. The mooring system is anchored to the bottom with heavy anchors (as illustrated below). Out of this anchoring system a number of cables protrude which connect to the cages and thus anchor the cage so that it cannot move. This system is designed to withstand strong winds and large waves.
A number of mooring systems will be placed in several locations in the lake. Each of the systems will carry 24 cages. Each system will be named so it will be characterized and identified by the farm's computer.



Mooring Diagram                                                                                                        Anchor

Mooring System


Daily Operation


The cage system is serviced by a number of floating elements. The work between the cages is preformed using motorboats. The use of motorboats serves several purposes: stoking fish into the cages, harvesting fish from the cages, extracting fish to the processing plant, transferring fish between the cages, feeding the fish and a vast number of other activities requiring movement between cages and shore. In addition, the motorboat is used to move the whole cage to the shore for harvesting, restocking or net preparation.
Team Boat

Stoking and harvesting fish can also be done by using special fish tanks on the service boats that contain water with oxygen, which comes from a special bottle of oxygen. The extraction of the fish is done part by hand and part by mean of a special device for the extraction of fish called the Archimedes Screw (Fish Elevator).




Fish Elevator
At a central point in the lake a wharf will be located to serve the cages by the boats. The wharf will be the main service point which will concentrate all cage related matters such as loading and unloading of food sacks, fuel station, repair and maintenance of the cages, exit point for the divers and a place to tie up the boats at night, and to leave extra floating technical elements.

From time to time, when the cages are emptied of fish, the nets will be transported to shore and washed in a specially designated facility. The fish farm will be serviced by a number of divers whose role will be to watch for damage to the cages, repair the nets in case of tears caused by predators or by any other causes.                                                                                                                                  Elevator for fish harvesting

 

 

Feeding system

Correct fish feeding is one of the more important factors in a fish growing system in general and especially when feeding caged fish, as fish feed is the biggest expense in fish farming. There are several fish feeding methods for caged fish. Each system has its qualities and costs. The feeding system selected by our experts is quite simple and best suited on, a feeding system using a feeding boat with a feeding gun.

Feeding Boat

The fish food arrives at the fish farm directly from the food processing plant. It comes in bags of 25 kg each or big bags that are unloaded and placed in a special storing facility.





Feeding Canon
Fish feeding in the cages farm is done using boats on which a special food container is placed. A specially operated system sucks in and thrusts out the food by high air pressure directed outward towards the fish cages. This system is called a "feeding gun". The containers placed on the boats hold 3-4 tons of feed. This floating feeding system is designed to pass between the cages and feed each cage according to an orderly feeding list which the boat operators receive prior to feeding time. The cage farm will hold and operate 2 such feeding boats in rotation throughout the day, feeding each cage 3 to 4 times a day. Repeated fish feeding is important in order to ensure proper usage and good digestion of the feed.  Contact us: uribenis@gmail.com                                                                                                           

                                                                                                                                          

                                                                                                                                                                                               Daily Feeding Program                                                                                                                                                      Feeding canon    


Daily Feeding Program