WP/81/SPH/CP-20
by
Pinij Kungvankij1
1. INTRODUCTION
Research on shrimp propagation in Thailand started since 1968. Three fishery stations were assigned to conduct research; these are Phuket, Songkhla and Rayong stations. In 1970, the experiment on spawning, developmental stages and feeding were completed. In 1972, the Government of Thailand has set up the project called "Shrimp Culture Project" under the assistance from the Japanese government to concentrate on mass production of marine shrimp seeds and the distribution of seeds PL 22 to farmers for intensive culture of this species.
At the beginning, shrimp hatcheries in Thailand were based on the Japanese system for the mass production of Penaeus merguiensis and P. monodon seed. However, there are differences in conditions and the problem of the lack of spawners of P. monodon occured. Later on, the method of induced spawning by eyestalk ablation was initiated, but the results were not satisfactory during the first phases.
In 1977, the small tank hatcheries (Galveston system) become very well-known all over the world. Since this system is completely different from the Japanese system and the remaining facilities (Japanese type) must be used, a study on the advantages and disadvantages of these two systems were made and the following observations were found as enumerated below.
1.1 Galveston system
1.1.1 Advantages
1.1.2 Disadvantages
1.2 Japanese system
1.2.1 Advantages
1.2.2 Disadvantages
On the purpose to utilize all the facilities and introduce new techniques Satul Fisheries Station has modified the new system called a modified system (Satul system) by combining the advantages of both systems together which should give very good results.
2. CONSIDERATIONS IN SITE SELECTION
2.1 Water supply
The site should be located near sandy or rocky shores where clear seawater can be obtained and free from pollution. The quality and quantity of seawater must be suitable for hatchery work. It should be possible to get freshwater from public water supply.
2.2 Availability of spawners
It should be possible to obtain spawners either from wild stock or rearing ponds. The site should have enough ground to construct the rearing ponds, and is close to the fishing ground of gravid females.
2.3 Availability of electricity
The site should be provided with a public power source. Since the hatchery must use electricity to operate the facilities such as marine pump, air blower, etc.
2.4 Good transportation
The site should be near the rearing ponds and accessible by road for convenience in distribution of postlarvae. It should also be convenient in transporting supplies and other necessities for the hatchery and staff.
3. DESIGN OF THE HATCHERY
3.1 Hatchery tank
3.1.1 Typical type
The typical type hatchery is based on the Japanese system. Rectangular or square concrete tanks vary from 16 to 100 tons in capacity, 1 meter in depth is commonly used. The water inflow, outflow and aeration are adjusted in suitable conditions.
3.1.2 Modified type (Satul type)
There are three separate spawning, hatching and rearing tanks. The spawning and hatching tanks are round 1.5 ton in capacity. They are constructed of fiberglass. The bottom is either flat or cone-shaped. Water is aerated by lead-weighted airstones suspended from the side of each tank.
3.2 Live food rearing material and tanks
There should be flat bottom flasks for continuous culture in the laboratory, 20-liter culture carboy, 1.5 ton fiberglass tank and at least 20 percent in capacity of larval rearing tanks are used as algae culture tanks.
3.3 Air supply system
Adequate aeration is necessary throughout the course of larval rearing to hold eggs in mid-water and to maintain adequate oxygen level.
4. OPERATION AND MANAGEMENT
4.1 Rearing water
Seawater is filtered through a 180–200 mesh filtering net to remove debris and large plankton animals. However, diatoms will pass the filtering net to the tank. Turbid coastal water should be filtered through layers of fine sand to eliminate suspended material.
In typical type hatcheries, only half of each tank is filled at the beginning. The water level is then gradually increased by the addition of filtered seawater and pure culture of diatoms. The tank will be filled to full capacity when the larvae reach mysis stage.
4.2 Spawners
Spawners can be collected both from the sea by trawling or gillnet or from the rearing ponds. These collected shrimps are induced to maturate by eyestalk ablation.
4.3 Technique
4.3.1 Typical type
Gravid females are placed in the hatchery tank at the rate of 1 per 3–4 tons and 1 per 10 tons of tank capacity for P. merguiensis and P. monodon, respectively. Spawning usually occur on the first night, and the spawners are removed in the morning of the next day. The shrimp larvae are reared in this tank until the attain postlarval stages in 20–22 days.
4.3.2 Modified type (Satul system)
Spawner is placed individually in 1.5 tons fiberglass tank. The spawner is removed in the morning after spawning. The eggs are collected by siphoning, then washed and placed into the hatching tanks.
After hatching out, the nauplius larvae are counted, by approximation and transferred to other 1.5 ton fiberglass tanks at the rate of 200 000 nauplii per tank. The larvae are reared in 1.5 ton tanks until mysis stage, then they are transferred to 50 ton rectangular concrete tanks with density of 15 larvae per 1 liter of water and reared up to postlarvae for 20–22 days.
5. FEEDS AND FEEDING
5.1 Nauplius stage
During this stage, the larval shrimp use food stored in its yolk sac. However, for typical type system, diatoms are supplied to the hatchery tanks in order to make them bloom to serve later as food for the protozoea.
5.2 Protozoea stage
Larvae in this stage should be fed by various kinds of phytoplankton such as Chaetoceros sp. and Tetraselmis sp. However, the protozoea larvae does not have much ability for finding food. Thus, it is necessary to provide proper amount of food so that the larvae can get them easily. The optimum density for feeding is approximately 5 × 104 cells/ml.
The size of diatom must be related to the mouth size of the larvae. It is found that suitable diatom for each substage of protozoea should be as follows: Chaetoceros for Protozoea I and Tetraselmis for Protozoea II and III.
5.3 Mysis stage
Larvae in this stage should be fed with rotifer (Brachionus plicatilis). The number of rotifers required depends on the density of shrimp larvae. Each mysis consume an average of 100–200 rotifers per day.
Artemia salina is used to feed shrimps in early stages of postlarva (about 4–5 days), and minced clam meat is used as a food in later stages (Figure 1).
6. HATCHERY TANK MANAGEMENT
The larvae are normally sensitive to the change of environmental conditions, particularly in protozoea stages. The most important factor are water temperature, salinity, pH and amount of nitrogen compound (NH3-N, NO2-N) in water.
To maintain good condition in the breeding tank, the following work should be done:
Water temperature, salinity, pH, nitrite-nitrogen and ammonia-nitrogen in water should be checked daily.
For typical system add about 10–20 cm height of clean and filterated freshwater every day. For modified type (Satul type), 10 to 30 cm height of sea-water have to be changed daily while the larvae are in the protozoea stage.
From mysis stage to postlarvae 20–22, one third of seawater have to be changed every day.
Get rid of excess food that may pollute the water.
7. HARVESTING OF SEED AND TRANSPORTATION
The seed in hatcheries can be collected by bag net tied at the outlet pipe. The larvae are drained out into water.
The seed are placed in polyethylene bags (28" × 32"). Each bag contain 5 liters of filtered seawater. The number of seed is about 3 000–5 000 postlarvae per bag, depending on the transportation time. Oxygen is injected into the bag before sealing. The seed bag is then put into the empty paper box or plastic container just big enough for the bag fit in firmly. The temperature in the container is controlled at around 20–22°C, by ice mixed with sawdust or the transportation can be made in airconditioned bus.
Legend:
E - Egg
N - Nauplius
Z - Zoea
M - Mysis
PL - Postlarva
Fig. 1. Feeding programme for penaeid shrimp hatchery
