CAGE CULTURE OF FIN FISH (GROUPER, MILKFISH, SIGANID, SEA BASS, SNAPPER, ETC.)
Details:
I. INTRODUCTION
Cage culture of marine fish provides alternative livelihood for sustenance fisherfolks. This has been a popular method of rearing fish in the sea coast. This technology is cheap to operate because it needs only small area and less physical facilities. A Floating Cage is a moveable cage with floating units from which a single cage or a series of net cages is suspended. A Stationary Cage is tied to fixed poles at their corners or anchored.
Due to their high market value especially when sold alive, finfish like grouper, siganids, seas bass and snapper are now cultured in commercial scales in other regions of the country and in other countries like Kuwait, Indonesia, Malaysia, Thailand, Hong Kong, Taiwan, Japan, China and Mexico. Some private companies have ventured in finfish cage culture and they appear to have survived and prospered.
II. METHOD OF OPERATION
A. Site Selection
1. The culture site should be accessible by land and water transportation.
2. Any conflict with other fishery and maritime activities in the area should not be ignored.
3. The site should be free from any pollution sources.
4. Availability of seed stocks of that species to be cultured in the area is very important.
5. Well-oxygenated and directly influenced by open sea water, especially coves protected from strong monsoon winds is a good site.
6. Average depth of water within the area should be around 3 meters at zero tide.
B. Culture Method
Environmental factors in the area must be considered before cages are installed. In those areas that are exposed to periodic strong swell and wave actions, cages require greater material strength. Cage can be of any size but must be lightweight, durable and less expensive.
1. Construction of Raft and Cages
A large raft (10.6 m X 7.2 m) is constructed with six (6) 10.6 m and eight (
7.7 m bamboo poles, each of 5"-6" diameter. Galvanized wire (SWG No.12) will be used in fixing the bamboo poles.
Small pieces of bamboo poles 6-8 m long and 5-7.5 cm (2"-3") diameter are installed at the top of the raft to serve as working platforms.
Styrofoam drum, plastic carbuoy or container of 60 liters volume are fastened to the underside of the bamboo poles by means of nylon ropes.
A 3 m X 3 m cage made of polyethylene netting with mesh sizes of 25mm, 12mm and 50mm are used for stocking of juveniles, nursery of fry and for fattening purposes respectively.
A square frame of galvanized iron-pipe (2.8m2 20 mm diameter) is fixed at the bottom to distend the cage.
The cage is suspended under a division of the raft by a set of four nylon ropes (10mm diameter) each of which threads vertically through the meshes of the netting and connects a corner of the bottom square frame to the raft. Another set of ropes are installed without threading through the netting, and it is used for hoisting up the cage for harvesting.
The raft is anchored in position at each corner by a 40 kg iron anchor with a nylon rope of 20mm diameter.
Cement blocks or strong tree trunks driven into the bottom can be used in place of the anchors. The anchoring rope should not be too tight so as to allow for tidal difference and to provide a flexible hold without over-straining the raft at low tide.
2. Stocking of Cage
Each net cage should best be stocked with juvenile fish at a size of about 100g at the rate of 14 fish per cu.m. Farming period would only take about 6-9 months for the fish to reach marketable size. Stocking should be done separately for each size group to prevent cannibalism. Stocking density up to market size varies from 10 to 100 fish per cubic meter.
3. Feeding of fish
Trash feeding (consisting of Tilapia mossambica and other small fishes) is considered suitable for the chosen species. The trash fish could be obtained by purchase from fish landing sites or in public markets.
The simple method of feeding caged fish is recommended, i.e. by hand feeding. The caged fish should be fed twice daily: early in the morning and late afternoon. The trash fish should be small enough to be taken by the fish. In feeding, it is better to spread the feed as evenly as possible to ensure all fish having the chance to reach for the food.
The amount of trash fish to be fed depends mainly upon the size of the fish and the water conditions such as the water temperature. The quantity of feeds is anticipated to be about 6% of the biomass of the caged fish and the fish are expected to be satiated with food within 15 minutes of eating.
Caution should be observed not to overfeed the caged fish in order to avoid not only wastage of food but also serious ill-effects on the health of fish due to the decaying of the uneaten food.
4. Maintenance operation
Regular maintenance on the rafts and cages should be carried out to ensure that all the materials are in good condition and properly secured.
The submerged cages could be clogged easily particularly in the case of smaller mesh-sized netting. Monthly cleaning of the net should be done.
Some fish tend to grow faster than the others despite efforts to spread the food evenly. It is desirable to sort the fish periodically according to size, putting the larger fish in one cage and the smaller fish in another. Mortality or disease should be checked.
C. Harvesting
Harvesting of cultured fish in cages can easily be done. The cages with market-sized fish are brought close to the shore and the fish are collected by means of scoop net. Harvested fish are then counted and weighed.
Harvesting of uniform-sized fish of high quality is an advantage in this kind of fish culture. However, harvesting depends largely on the requirements of the buyer. There is no definite schedule followed as harvesting is done when there is a demand for the fish.
D. Marketing
Marine fish commands a high price from P80.00 up especially when marketed fresh. Grouper has high sales value in local as well as overseas market throughout the year.
Source of Information : Bureau of Fisheries and Aquatic Resources (BFAR) Regional Office IX
Sources:
1. Basa, Sofia S., Finfish Cage Culture: An Income Generating Project.
2. AQUA FARM NEWS, Vol. X No.3 (May-June 1992)
soruce:neda
