3. HATCHERY DESIGN AND CONSTRUCTION

Basically, there are two hatchery systems being adopted. The large-tank hatchery which was developed in Japan is still the popular system applied in many Asian countries such as Taiwan, Thailand, Philippines and Indonesia. The small tank hatchery which originated from Galveston USA, has been applied in the Philippines and to same extent in Malaysia and Thailand. Recently a modification of the above systems has been developed which combined the beneficial characteristics of both systems taking into consideration the limitation of spawner supply.

There are three determinants in designing a hatchery viz: target species, production target and level of financial inputs. Although multi-purpose hatchery design for shrimps and finfish may not necessarily be the same. In any case, the target species must be clearly identified before designing the hatchery.

Production target can be determined based on a market demand and financial input. In the case of species such as Penaeus monodon at which the production of fry depends on the availability of spawners from the wild, production target is limited by the supply of spawners. This limits the production capacity of the hatchery. Whereas in P. japonicus and white shrimps at which spawners are easily available, production capacity is unlimited. Tank capacity up to 2500 cubic meters can be seen in many large-scale hatcheries in Japan where P. japonicus is the primary species grown. However, in most Southeast Asian countries where tiger shrimp (P. monodon) forms the target species for hatchery production, tank capacity is considerably reduced due to limited spawner supply from the wild.

Hatchery design is aimed at achieving the production target which determines the size of the hatchery. The tank capacity is based on an approximate ratio between algal culture tank and larval rearing and nursery tanks. Desirable algal tank capacity is 10–20% of the larval rearing tank capacity. The capacity of maturation tank depends on the number of spawners needed. Method of estimation of tank capacity for various rearing and holding tanks are given in the following examples:

Example 1. To estimate the holding tank capacity used in a big hatchery system (spawning, larval rearing and nursing utilizing the same tanks).

Production target: 10 million post larvae (PL25)

Number of runs per year: 7
Duration per run: 40–45 days including tank preparation, etc.
Production target per run: 1.5 million P25

Production rate of nursing tank: 3000 Pl/ton
Total hatchery holding tank capacity needed: 500 tons
Algal culture tank: 50 tons (10% of larval tank)

Example 2. To estimate the tank capacity for larval, nursery, algal culture and maturation tanks.

Production target: 10 million post larvae (PL25)

Number of runs per year: 10
Duration per run: 30–35 days including tank preparation, etc.
Production target per run: 1 million (PL25)

Production rate in larval nursing tank: 3,000 PL25/ton

Total larval nursing tank capacity required: 350 tons

Survival rate in nursery: 50%
Total number PL1 needed for stocking in nursing tank: 2
million/run

Production rate from larval rearing tank needed for 1 nursing tank’s run: 50–60 tons
Duration of larval rearing tank: 12–15 days
2 runs in larval rearing tank = 1 run in nursing tank
Actual capacity of larval tank needed %/run: 25–30 tons
Survival rate from nauplii to P1: 30–40%

Number of nauplii needed for larval tank: 6–7 million
Since average hatching rate: 70%
Total eggs required: 8–10 million
Average number of eggs per spawner: 400,000 eggs
Number of wild spawners needed: 25–30 per 15 days

or

Since number of eggs produced by ablated spawners = 200,000
Total number of ablated spawners needed: 60–120
Stocking rate of ablated spawners: 5–6/ton
Capacity of maturation tank: 48 tons or four 12-tons

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