The following assumptions were used to define the size and equipment needs for a pilot-scale government hatchery, complete with some demonstration ponds, in lower Sindh province, Pakistan. The budget for this facility is given in Appendix 7.
CAPACITY OF FARM
The consultant originally intended to size the facilities so that the hatchery could supply sufficient post-larvae to enable the production of 3 g juveniles for stocking up to 1 ha of government demonstration ponds and 5 ha of private ponds. These criteria were doubled, to 2 ha of government and 10 ha of private ponds respectively, following debriefing with the GOS.
The government hatchery and demonstration farm should therefore be capable of producing:
- up to 3 000 kg of freshwater prawns per year from its demonstration ponds;
- sufficient postlarval prawns to supply:
internal requirements to demonstrate and provide training in nursery and grow-out technology;
requirements of farmers wishing to stock a total of 10 ha of grow-out ponds at stocking rate of 5m2/yr of 3 g animals.
PRODUCTION PROCESS
The hatchery will operate a “clearwater” larval system consisting of a 10-day first phase stocked at 250/l, followed by a second phase of up to 25 days stocked at 50/l. After metamorphosis at the end of the second phase, postlarvae will be held in tanks for a further 15 days stocked at 5/l. The hatchery will operate at least four complete cycles/year. More than half of the postlarvae produced in the first batch will be used to stock the governments own nursery ponds for demonstration purposes. The total output of each cycle will be transferred to nursery ponds. Higher stocking densities in both larval rearing phases are employed elsewhere but are not recommended in the initial stages of development. However, such improvements later will enable the facilities to be used more efficiently and enable annual output of postlarvae to be increased without further capital cost.
Nursery ponds will be stocked at 50/m2 and animals will be reared to 3 g within 2 months.
Demonstration grow-out ponds will be stocked at 5/m2 and operated for 6–8 months to produced average 40 g marketable animals. Annual target output of grow-out ponds is 1 500 kg/ha.
GOVERNMENT FACILITIES REQUIRED
Government nursery and grow-out demonstration ponds
To produce 3 000 kg/year within the government facilities from a stocking rate of 5/m2 of 3 g animals and assuming a 75% survival rate during grow-out, four 0.5 ha grow-out demonstration ponds are recommended.
The requirements for 3 g animals will total 600 000 (500 000 for the private sector, enabling the stocking of up to 10 ha at 5/m2) and 100 000 to stock the government grow-out ponds at the same rate). The total requirement for government nursery ponds, assuming that they are stocked with p1–15 animals at 50/m2, that each nursery pond is used twice per year for two-month rearing periods, and that the nursery survival rate is 75%, will therefore be 0.8 ha. Four 0.2 ha nursery ponds are recommended.
Summary of pond requirements:
- 4 of 0.5 ha
- 4 of 0.2 ha
Government hatchery tank facilities
To stock the government nursery ponds defined above 800 000 p1–15 animals will be required Assuming that an 80% survival rate is achieved, 1 000 000 newly metamorphosed animals will be required. Stocked at 5/l, this will require a total postlarval tank capacity of 200 000 1 (200 m3). Assuming that these tanks are used four times, each for a 15-day cycle, the total volume required will be 50 m3. Two 25-t postlarval tanks are recommended. These tanks will have flow-through water exchange, so no biological filtration tanks will be required.
Assuming a survival rate of 62.5%, the production of 1 000 000 newly-metamorphosed prawns will require space to stock 1 600 000 10-day old larvae. Total phase-II tank volume requirements, at a stocking rate of 50/l will therefore be 32 000 1 (32m3). Assuming that the tanks will be used for at least four 25-day cycles, the actual tank volume will be 8 000 m3. Three 3-t phase II larval rearing tanks are recommended, giving some excess capacity. Allowing 50% of rearing volume for filtration, three 1.5 phase-II filter tanks will also be required for biological filtration (these will not be required if the hatchery is managed on a flow-through water exchange system).
At a phase-I survival rate of 80%, the production of 1 600 000 10-day larvae will require space to stock 2 000 000 newly hatched larvae. At a stocking density of 250/l, total phase-I larval tank space will be 8 000 1 (8 m3). At four cycles per year, the actual volume will be 2 m3. Two 1-t phase I larval rearing tanks are recommended. Allowing 50% of rearing volume for filtration, two 0.5-t phase-I filter tanks will also be required for biological filtration (these will not be required if the hatchery is managed on a flow-through water exchange system).
In addition, tanks will be required for hatching Artemia nauplii. Allowing for up to 10 BSN/day/ml for phase-I larval tanks, and 5 BSN/day/ml for phase-II tanks, a total of 1 325 million BSN will be required per cycle. For four cycles, 5 300 million BSN will be needed. At 250 000 cysts/g and 80% survival rate, this will require a total of 26.5 kg of cysts. [For costing purposes, 30 kg of cysts has been allowed]. The maximum number of BSN required per day will be 75 million nauplii (equivalent to 375 g cysts). At a stocking rate of 1 g/litre, this will require 375 litre of hatching tank volume. Two 0.2 m3 Artemia tanks should be adequate.
Berried females will be obtained, after the initial introduction (see Section 2.2.), from government and private grow-out ponds. It should not be necessary to have more than 17 berried females in the hatchery at any one moment. Three 1-t broodstock tanks would be adequate. [IMPORTANT NOTE: As noted earlier, higher larval stocking densities for both larval rearing phases may be practicable when local experience has been gained. This, and an increase in the number of rearing cycles, could markedly increase the potential output from this hatchery.]
Government water and water mixing facilities for hatchery
The following assumptions and calculations have been used to size the water treatment and mixing tanks for the hatchery:
- although each larval tank should have its own recirculation system, provision has been made for daily 50% water exchange in all larval rearing tanks in case a flow-through system is finally selected. The postlarval tanks will be operated on a 200% per week water exchange system but, apart from filtration, the water will not be chlorinated; therefore, no provision for storing freshwater for postlarval tanks. At 200% exchange per week, the postlarval tanks will require 50 × 2/7 = approx 15 m3/day will be required;
- all larval tanks will be operated at 12 ppt. Assuming available seawater is 35 ppt, approximately one third of the larval water requirement will be seawater;
- total water content of all larval tanks (excluding biological filters) will be [2 × 1 000] + [3 × 3 000] = 11 000 1. At a daily 50% exchange, some 5 500 1 of 12 ppt water (approx. 2 000 I/day seawater and 4 000 I/day freshwater) will be needed.
The seawater storage tanks should have a volume of at least 7 × 2 000 – 14 000 1 (say three 5-t seawater tanks) and the freshwater storage tanks should have a volume of 7 × 4 000 = 28 000 1 (say three 10-t freshwater tanks). In addition two brackishwater mixing tanks will be required (one being mixed; one being used). Since UV disinfection is recommended, these tanks only need to be of sufficient volume for about one day's supply each (say two 5-t brackishwater tanks).
The freshwater requirements of the broodstock tanks will be minimal. In summary, the following tanks are required for the hatchery:
| (t) | # | |
| 0.2 | 2 | (Artemia) |
| 0.5 | 2 | (phase-I filter) |
| 1.0 | 5 | (2 × phase-I larval; 3 × broodstock) |
| 1.5 | 3 | (phase-II filter) |
| 3.0 | 3 | (phase-II larval) |
| 5.0 | 5 | (3 × s/w and 2 × b/w) |
| 10.0 | 3 | (f/w) |
| 25.0 | 2 | (postlarval) |
WATER AND AIR PUMPING REQUIREMENTS
No special provision has been made for the water or pumping requirements for the nursery and grow-out ponds; it has been assumed that sufficient capacity is already available on the Chilya site. Similarly, the raw freshwater requirements of the hatchery should pose insignificant extra demand.
However, a new requirement will be for seawater. Unless/until recirculation is used in the freshwater prawn hatchery, there will be a demand of 14 m3/week. This would need to be trucked from Hawkes Bay to Chilya if that option were taken, necessitating bowser hire or purchase. Purchase is suggested because the bowser truck could also be used for transporting juvenile prawns to private farms. However, seawater transport will not be required if the hatchery is positioned at Hawkes Bay.
