Prepared by S.M. de Silva, Research Officer,
Colombo, 17 October 1980
Introduction
The practice of cage culture is new to Sri Lanka and is still in the preliminary experimental stage. The first attempts were carried out in the main body of the Negombo lagoon, beginning in March 1979. As the first location was found unsuitable, a pilot project was established on an inlet to the Negombo lagoon, the Dandugan Oya. The pilot project has been in operation since July 1979, and one harvest was completed in January 1980.
Present position
Cage culture is being developed in Sri Lanka through a number of projects. They are:
Research project: In collaboration with the Department of Zoology, University of Ceylon, Colombo Campus. The objectives of this project are to use a number of species which have a potential for brackish and fresh water cage farming to determine suitable cage designs and sizes, appropriate feed and feeding regimes, stocking densities and rate of growth, optimum rearing period and economics of production.
IDRC funded programme: The objectives of this programme are:
To determine the applicability of cage culture systems in lakes and tanks and other inland waters using various fresh water species.
To determine the potential economic value of technologically sound systems, and identify constraints to adoption.
To train Sri Lankan research and extension workers in research techniques and the demonstration and implementation of acceptable technologies.
To cooperate with rural farmers and fishermen in the development and implementation of cage culture techniques
Extension programme of the Ministry of Fisheries: The objectives of this programme are to disseminate information, techniques and experience gathered from the research project, the IDRC programme and other studies.
Sites
At present cages are being operated as follows:
Research Project
| Dandugan Oya | - Brackish water | ||
| No. of cages: | 01 wooden | (2 × 2.5 × 1.75 m) | |
| 02 bamboo | ( - do - ) | ||
| 05 P.V.C. | ( - do - ) | ||
| Fish varieties: | T. nilotica, T. mossambica, Etroplus suratensis | ||
IDRC
| 1. | Bolgoda lake - Brackish water | |
| No. of cages: | 12 - of bamboo platform and empty metal drums as floaters | |
| (3 × 3 × 2.5 m) | ||
| Not yet stocked | ||
| 2. | Parakrama Samudra - Fresh water (Polonnaruwa) | |
| No. of cages: | 12 - of bamboo platform and metal drums as floaters | |
| (3 × 3 × 2.5 m) | ||
| Fish variety under experimentation: T. nilotica | ||
| 3. | Udawalawe Reservoir - Fresh water | |
| No. of cages: | 12 - bamboo platforms with metal drums as floaters | |
| (3 × 3 × 2.5 m) | ||
| Fish variety: | T. nilotica | |
| 4. | Gregory lake - Fresh water | |
| No. of cages: | 12 - bamboo platform with metal drums as floaters | |
| (3 × 3 × 2.5 m) | ||
| Fish variety under experimentation: Rainbow trout | ||
| 5. | Udukiriwela tank - fresh water | |
| No. of cages: | 4 (3 × 3 × 2.5 m) | |
| 4 (3 × 6 × 2.5 m) | ||
| Bamboo platform with metal drums as floaters (not yet stocked) | ||
| Suggested fish variety under experimentation: T. nilotica | ||
Ministry Extension Project
| 1. | Tabbowa tank - fresh water |
| No. of cages: 12 (2 × 2 × 2.5 m) completely of bamboo structure | |
| Fish stocked - T. nilotica | |
| 2. | Wennappuwa tank - fresh water |
| No. of cages: 10 (3 × 3 × 2.5 m) completely of bamboo structures | |
| Fish stocked - T. nilotica, Common carp | |
| 3. | Batticaloa lagoon - brackish water |
| No. of cages: 4 (3 × 6 × 2.5 m) (P.V.C. pipes and plastic barrels) | |
| Not yet stocked | |
| Suggested varieties: Groupers (Ephinephelus), Snapper (Lutianus argentimaculatus), Lates sp. |
Feed
At Dandugama Oya research project, feed is produced using locally available materials like ox blood, copra meal and rice bran. These are compounded and turned out as pellets (3 mm diameter) using a locally available hand mould.
For other IDRC and Ministry extension projects, specially compounded pellets are prepared from fish meal, chicken mash and rice bran according to a predetermined formula. This pellet feed is prepared in bulk at the Institute of Fish Technology and transported to the various project sites. Average crude protein percentage of this pellet is 25.
For rainbow trout a pellet feed is compounded fresh on the site using ox blood, meat offal, chicken mash and brewers yeast as the main components. Feeds of this type with three different crude protein contents are the subject of trial. For T. nilotica stocks are fed with rice bran instead of pellets for comparison purposes. Attention is now being given to feeding the rice bran in the form of pellets.
Results
Dandugama Oya Project - After the first six months rearing period, under two stocking densities of 50 fish/m3 and 75 fish/m3, average weight of fish harvested was 220 g and 200 g respectively.
IDRC Programme and Ministry extension programmes - All cages in the projects mentioned above were put into operation very recently (after July 1980).
Cost of Cage Construction
Design I
Construction costs of frame only, which can accommodate four 3 × 3 × 2.5 m net cages
| 12 bamboos (25 ft each) at Cey.Rs. 20 per bamboo | Cey.Rs. | 240.00 |
| 9 45 gal empty drums at Cey.Rs. 125 per drum | 1 125.00 | |
| 4 litres anticorrosive paint at Cey.Rs. 20 per litre | 80.00 | |
| 20 lbs coir rope at Cey.Rs. 3 per lb | 60.00 | |
| 400 m 3 mm Kuralon rope at Cey.Rs. 70 per 100 m | 280.00 | |
| Labour: 25 man-hours at Cey.Rs. 4 per man-hour | 100.00 | |
| Total Cey.Rs. | 1 885.00 |
Construction costs for net cage (3 × 3 × 3 m
| 45 m2 of nylon nets (9 ply, 10 mm) | 175.00 | |
| 1/4 lb 12–18 ply Kuralon twine at Cey.Rs. 40 per lb | 10.00 | |
| 8 man-hours at Cey.Rs. 4 per man-hour | 32.00 | |
| Total construction cost for 4 net cages | 868.00 | |
| Total cost of construction for a unit consisting of a frame and 4 net cages | Cey.Rs. | 2 753.00 |
Design II
Construction costs for cage frame made of 1.5" P.V.C. pipes and empty plastic barrels (which can accommodate two 3 × 4 × 2.5 m net cages)
| 40 m 1.5" P.V.C. piles at Cey.Rs. 31 per m | Cey.Rs. | 1 240.00 |
| 4 1.5" P.V.C. ‘L’ joints at Cey.Rs. 22 per piece | 88.00 | |
| 8 1.5" P.V.C. ‘T’ joints at Cey.Rs. 24 per piece | 192.00 | |
| ⅛ pint P.V.C. glue at Cey.Rs. 80 per pint | 10.00 | |
| 6 6 gallon empty plastic barrels at Cey.Rs. 90 per barrel | 540.00 | |
| 6 man-hours for assembling at Cey.Rs. 4 per man-hour | 24.00 | |
| 50 m of 3 mm Kuralon rope at Cey.Rs. 68 per 100 m | 34.00 | |
| Total Cey.Rs. | 2 128.00 |
Construction cost for 3 × 4 × 2.5 m net cage:
| 55 m2 net 9 ply | Cey.Rs. | 215.00 |
| 52 m 5 mm Kuralon rope | 75.00 | |
| ¼ lb 18 ply Kuralon twine at Cey.Rs. 40 per lb | 10.00 | |
| 8 man-hours for mending at Cey.Rs. 4 per man-hour | 32.00 | |
| Total Cey.Rs. | 332.00 | |
| ∴ Total cost of construction for 2 such net cages | Cey.Rs. | 664.00 |
| Total cost of the unit which can hold 2 net cages of 3 × 4 × 2.5 m size | Cey.Rs. | 2 792.00 |
Design III (made up of 3" diameter bamboos only - which can accommodate four 3 × 3 × 2.5 m net cages)
| 30 3" diameter (25 ft) bamboos at Cey.Rs. 20 per bamboo | Cey.Rs. | 600.00 |
| 1 000 m 3 mm coir rope at Cey.Rs. 0.10 per m | 100.00 | |
| 100 m 3 mm Kuralon rope at Cey.Rs. 7.00 per 100 m | 70.00 | |
| 25 man-hours for assembling at Cey.Rs. 4 per man-hour | 100.00 | |
| Total Cey.Rs. | 870.00 |
Construction cost for net (3 × 3 × 2.5 m)
| 45 m2 nylon net (9 ply - 10 mm) at Cey.Rs. 4 per m2 | Cey.Rs. | 175.00 |
| ¼ 1b 12–18 ply Kuralon twine at Cey.Rs. 40 per 1b | 10.00 | |
| 8 man-hours for assembling at Cey.Rs. 4 per man-hour | 32.00 | |
| Total Cey.Rs. | 217.00 | |
| ∴ Total construction cost for 4 net cages | Cey.Rs. | 868.00 |
| Total cost of construction for a unit of cage consisting of 4 net cages | Cey.Rs. | 2 753.00 |
The above designs of cages are meant solely for experimental purposes, hence the costs shown for the construction of cages cannot be taken for cost benefit evaluation purposes.
