Stock fish either early in the morning or late in the afternoon when the water is relatively cool. Acclimatize the fingerlings before stocking them. To do this, float bags of fingerlings in water where the fish is to be stocked, thereby allowing the water on the bags to float on the pond for 30 minutes. Determine the water temperature of both bag and pond waters with a thermometer.
A difference of more than 30°C may cause eventual death of stock. Open the bags and introduce water gradually from the pond to the plastic bags until the temperature is almost the same. Let the fingerlings get out freely from the bags.
The number of fingerlings to be stocked in a cage varies from 10 – 15 pieces per cu m to reach a size of 100 g each in 150 days without supplementary feeding during summer months. Use the same density at the start of the rainy months up to early part of summer. However, the growth rate is lower during rainy months because the water is cooler and there is little presence of natural food in the water.
Management of Tilapia in Cages
Tilapia in cages require minimal care and maintenance. Aside from occasional intrusion of predators, mechanical damage to the net screen and poaching, no serious problem can be expected.
Feeds and Feeding
Feeding of tilapia in cages is necessary for higher yield especially if productivity of the surrounding water is poor. Feed ingredients are locally available and economical. Supplementary feeds given to the fish using 3-5% body weight as basis for food ration per day. Divide the ration into 4 portions at an interval of 2 hours adjusted directly after sampling. Place feeds in small plastic bags. Weigh and label carefully according to the number of cages to avoid error when feeding.
Before the onset of predictable bad weather, loosen anchor ropes and using a banca, tow all the units towards a sheltered area. Put additional anchors to strengthen the whole project units.
Maintenance of Support Facilities
Support facilities refer to the service “banca” raft, caretakers hut and other facilities in the project. The “banca” should always be in tip-top condition since this is the only available means of transporting the produce and for management personnel to supervise the project.
Protect plastic and pandan bags, styrofoam boxes, spare nylon net cages, nylon twine and other equipment from rodents. Repair leaking roof of huts to give ease and comfort to the project personnel.
This is a scheduled monthly activity of grading the fish stock into different size groups to reduce the adverse effect of uneven growth and association of “size hierarchies” within the fish population. Smaller fish are harvested later when they reach the desired size and weight.
Most cage operators buy tilapia fingerlings of size 22 when high quality fingerlings are now readily available. These are not directly stocked in grow-out cages; instead, they are reared for about a month in cages with a mesh size of no. 24. After a month, grade the fingerlings and transfer the bigger ones in cages with mesh size no. 17. Repeat the process until they are stocked in cages with mesh size no .14 where they are reared up to marketable size. This technique of grading the fish, called modular method, enables the cage operator to stock and harvest the fish continuously.
Care and Maintenance of Cages
For daily and routine work, check loose twine and torn meshes of the nets and repair immediately by mending or patching. Remove by brushing bio-fouling organisms such as freshwater algae, sponges and debris that set on nylon net as soon as they detected. Replace the whole cage with spare net cage, when may fouling organisms had accumulated obstructing water exchange.
Check the net screen everyday for wear and tear as there might be possible damage that leads to the escape of the fish stock. Dive occasionally and inspect the condition of nettings and other materials submerged under water.
The fish operator or caretaker acts as the overseer and plans ahead what are to be done on time. He must keep his co-workers well-informed of the activities to be undertaken. He must also follow the work plan, target and calendar of activities closely to attain its target production. In order to carry out the work plan and schedule, he must form a functional working team out of labor resources of the project. This approach allows everyone to undertake a given task and helps instill a general team spirit toward problem solving.
Before harvesting, prepare all the materials and equipment needed. Two to three persons can manage one fish cage.
Untie the top corners of the net and allow the bamboo raft to enter the rectangular area. Two harvesters lift the net and push the raft toward an end of the cage. Scoop out the confined fish at one end of the net and place these in pails. Sort according to size. Place sorted fish in transport containers.
Records keeping plays an important role in any production undertaking. By keeping records of the project, the fish-farmer can determine whether the project is a profitable business venture or not. The fish-farmer must have a record of all activities and expenditures undertaken so that the schedule of stocking and harvesting could be done on time. It is also important to record the weather condition prevailing from day to day. This will serve as a basis for planning.
source: STII and PCARRD