1. Purpose of analysis
The purpose of looking into the costs and earnings of potential cage culture is to form an opinion as to whether or not cage culture has a possibility of becoming economically attractive as a commercial or subsistance activity.
2. Types of cage culture
Cage culture can be carried out in a number of different ways. However, in most instances the fish is fed. The type of fish will determine the characteristics of the cage and the feed.
As ingredients for fish feed are expensive in Sri Lanka (see Annex 11), and fresh water fish (with the exception of those marine fish which can also be grown in fresh water like milkfish, lates and mullet) are inexpensive, the Mission concludes that cage culture of marine fish is more likely to succeed than cage culture of fresh water fish. In what follows, we will appraise cage culture of Tilapia nilotica, sea bass and groupers.
3. Tilapia culture
The proposed culture unit consists of one raft with 4 cages, each with an effective volume of 16 m3. T. nilotica is grown for periods of six months. Starting at 25 g, they would reach close to 300 g in this period.
It can be seen from Table 13.1 that the investment required for this unit is low. The expected value of production per year of operation will be several-fold the value of initial investments. Emphasis should, therefore, be placed on constructing purposeful cages, of durable materials. Use of cheap material is a false economy if thereby the risks that fish be lost are increased. The life of cages will depend upon how much effort goes into maintenance. Netting material exposed above water may have to be changed at least once every second year. The submerged part should last for five years.
It is evident from the figures in Table 13.2 that it is the feed which will make or break a commercial cage culture operation. In our appraisal, the cost of feed is between 50 and 60 percent of the total. The cage culture feed cost is a function of the conversion ratio (quantity of feed needed to produce 1 kg of fish) and the price of feed. From the point of view of cost, a feed that costs Cey.Rs. 4 per kg, and has a conversion factor of 3, is as suitable as a feed that has a conversion factor of 4 but costs Cey.Rs. 3 per kg. Both feeds would contribute Cey.Rs. 12 to the cost of producing 1 kg of fish.
Given the high incidence of feed costs in total costs of cage cultured fish, stocking densities should aim at getting maximum conversion ratios from use of feeds. There seems to be little point in attempting to bring down the fixed costs per kg of fish cultured by increasing the stocking densities if this would lead to slower growth, or to poorer conversion ratios.
Considering the break even price for cage cultured tilapia, the cage culture of this species is not economically justifiable. Even if the growth rate per day increased from 1.5 g to 2.0 g, and the food conversion improved (from 6.38 to 3), the profitability of culture would be doubtful. The break even price would then come to about Cey.Rs. 16/kg of fish. If the labour cost were placed at zero, the break even price would come down to about Cey.Rs. 10/kg. The culturist would still not be able to compete with itinerant vendors of tilapia selling their fish at about Cey.Rs. 5 to 6/kg.
4. Culture of snappers and groupers
The proposed culture unit consists of two rafts, each with six cages. A cage has an effective volume of 16 m3. The culture will be carried out for periods of six months. Fish will be placed in the cages at an average weight of 100 g; some will be smaller and some larger. The fish will weigh an average of 800 g at harvest.
An inspection of the last column of Table 24.2 reveals that also for grouper/snapper cage culture, the major cost will be the feed. The structure of costs is about the same as for the tilapia culture.
Although we have projected rapid growth (4 g/day), the culture does not appear to be commercially interesting. The break even price (Cey.Rs. 24/kg) is above that paid by the consumer. If the feed conversion ratio could be brought down to 3, and the price per kg of feed to Cey.Rs. 1.75, the break even price would become Cey.Rs. 14/kg of fish. This is still too high to be readily competitive with fish landed by capture fisheries. However, it is sufficiently close to warrant some trials.
Table 13.1 Cage construction and associated investments
| Items | Units | Cey.Rs. per unit | Tilapia1 | Grouper2 | ||
| No.of units | Cey.Rs. | No.of units | Cey.Rs. | |||
| Drums | each | 200 | 9 | 1 800 | 12 | 2 400 |
| Bamboo poles (8 m) | each | 20 | 12 | 240 | 20 | 400 |
| Anticorrosive paint | litre | 20 | 4 | 80 | 5.5 | 110 |
| Coir ropes | lb | 3 | 20 | 60 | 30 | 90 |
| Kuralon rope (3 mm) | m | 0.70 | 400 | 280 | 600 | 420 |
| Labour | m/h | 4 | 25 | 100 | 35 | 140 |
| Netting (1/2–1 in mesh) | m2 | 4 | 180 | 720 | 360 | 1 440 |
| Kuralon twine 12–18 ply | lb | 40 | 1 | 40 | 2 | 80 |
| Labour | m/h | 4 | 32 | 128 | 40 | 160 |
| Protective netting | m2 | 6 | 50 | 300 | ||
| Total | 3 448 | 5 540 | ||||
Table 13.2
Cost of operation and revenue per year1
| Items | Units | Cey.Rs. per unit | T. nilotica2 | Groupers3 | |||
| No.of units | Cey.Rs. | No.of units | Cey.Rs. | ||||
| Fingerlings: | Tilapia | each | 0.25 | 5 832 | 1 458 | ||
| Grouper | kg | 15 | 960 | 14 400 | |||
| Feed | kg | 2.50 | 9 920 | 24 800 | 38 000 | 95 000 | |
| Hired labour | m/year | 9 000 | 1 | 9 000 | 1 | 9 000 | |
| Netting material (inner) | m2 | 4 | 36 | 144 | 144 | 576 | |
| Netting material (outer) | m2 | 6 | - | - | 112 | 672 | |
| Miscellaneous | % | 10 | 3 540 | 10 | 11 900 | ||
Total recurring expenditures | 38 942 | 131 548 | |||||
| Depreciation | % | 20 | 690 | 25 | 2 770 | ||
| Interest | % | 10 | 2 898 | 10 | 9 760 | ||
| Total costs | 42 530 | 144 078 | |||||
| Kg produced | kg | 1 555 | 6 144 | ||||
| Break even price ex-cage | Cey.Rs. | 27.35 | 23.45 | ||||
| per kg | |||||||
| Feed conversion ratio | kg feed | 6.38 | 6.18 | ||||
| kg fish | |||||||
1 From the point of view of the investor
2 One raft, 4 cages
3 Two rafts, 6 cages each
Data used to calculate values and physical quantities inserted in Tables 13.1 and 13.2
1. Cages
Two cases are analysed - (a) Tilapia culture on a raft having 4 cages, and (b) culture of marine fish (groupers) on two rafts each containing 6 cages. Each cage has a volume of 28.3 m3 (1 000 cubic feet) under water. The cages used in marine water are surrounded by a heavy netting material.
2. Fingerlings
Tilapia. The fingerlings are collected in the wild and purchased at Cey.Rs. 0.25 each. They are stocked at a density of 45/m3. The fish weigh 30 g at stocking and have a 90 percent survival rate.
Groupers are bought at a price somewhat above the market price, Cey.Rs. 15/kg and are stocked at a density of 25/m3 when weighing 100 g each. They have an 80 percent survival rate.
3. Feed
Tilapia nilotica will be fed at 5 percent of body weight (leading to a 1.5 g/day average growth) with a mixture of rice bran, poonac and fish meal, at a cost of Cey.Rs. 2.50/kg.
Groupers will be fed a similar diet at rates varying with age from 10 percent to 3 percent of body weight. This is expected to lead to an average growth rate of 4 g/day.
4. Labour
The operations are of such a size that they will be suitable for a family. In those instances where more hands than those available in the family are needed, it is expected that neighbours will help. Someone should be continuously close to the cages. Therefore the appraisal includes wages for one man-year of unskilled labour time.
5. Production
Tilapia. At harvest the weight will average 300 g. The total weight per raft will be (0.3 kg × 0.9 survival × 45 fish/m3 × 16 m3/cage × 4 cages) = 777.6 kg. For two harvests/year the production will be 1 555 kg.
Grouper/Snapper. At harvest, the average weight will be 800 g. Survival is 80 percent. Total production for two rafts and two harvests/year will be (0.8 survival × 0.8 kg × 2 harvests/year × 6 cages × 16 m3 × 25 fingerlings/m3 × 2 rafts) = 6 144 kg.
