2. SEED PRODUCTION

2.1 Broodstocks quality

Intensification of shrimp culture production is limited by seed supply. On the other hand, the production of seeds in hatcheries depends on availability of broodstocks and quality of spawners. A healthy spawner is described with illustration in Figure 3.

Shrimp hatcheries still depend on broodstocks obtained from the wild although eye-stalk ablation technique to induce maturation of shrimp has been found to work very well. However, it has been reported to be more expensive to raise breeders in captivity than to buy the wild mature shrimps from the sea. Furthermore, it was found that the ablated shrimps are not good which results to low rate of survival. Fry produced from pond-grown ablated broodstocks are not as hardy as those from spawners obtained from the sea. This may be due to a combination of many factors such as nutrition, genetics and environment (Liao, 1986). More research in these problem areas are necessary.

In Taiwan, this problem is being solved by “sea ranching”. Pond-grown shrimps are released in suitable sites that are protected and recaptured after several months when they are mature. A recovery rate of about 15 percent was considered high enough to be profitable. In the Philippines, perhaps keeping them in enclosures at sea would provide higher recovery rate. This would ensure the supply of shrimp broodstocks all year round, thus, also ensure seed supply of better quality.

HOW TO TELL A HEALTHY P. MONODON

Figure 3. Illustration of a healthy spawner
Source: Tong Kuwan Aqua Development Co., Ltd.
RM 4 5F 218 TA Shun 3 Rd, Kaohsiung, Taiwan, Province of China

Shrimp ranching has been done in Japan, particularly in Hamana-ko Lagoon. Post-larvae of P. japonicus were released in the lagoon in 1978. For a five-year period, a total of 17.6 million postlarvae were released. This programme has become an extensive programme reaching a total of over 300 million postlarvae released. The main sites of releases were inlets, open or semi-open waters (Figure 4). The result of this programme showed that shrimp production in the area was 2.4 times greater than natural catches in open waters.

The advantages of shrimp ranching are (Uno, 1985):

1. increased supply of shrimp breeders and increased shrimp production,

2. stabilized production through adjust ment of the time in releasing the post larvae

3. additional recruitment to the natural population of shrimp not caught for breeding purposes

Hatchery technique of seed production of P. monodon is known and the application of shrimp ranching under Philippine condition could well be made. The use of sea enclosures like the fishpen would be a good approach to solve shrimp broodstock availability. Juveniles of shrimps produced from hatcheries could be released in coastal waters. However, the government should initiate the programme and set up specific areas for the purpose. Shrimp ranching could be allocated to small fishermen cooperatives in selected areas only. Otherwise, installation of enclosures at sea would also proliferate if not properly controlled. Guidelines for this purpose should be made; releases and recapture of juveniles should also be monitored.

Figure 4. Topography of Hamana-ko Lagoon showing bottom conditions and depth. (1) site of enclosure for nursery culture; (2) mouth of lagoon (Imakiriguchi)
Source: Uno, 1985

2.2 Shrimp hatchery operations

The development of shrimp hatcheries in the Philippines is quite haphazard in the sense that many hatchery facilities sprang up without adequate technical guidance. This was a result of private sector interest and enthusiasm in getting the profits quickly and be ahead of the rat race for money-making. As a consequence, several hatcheries, especially the big ones end up losing money for not being able to operate them viably for several reasons.

Further refinement in hatchery management technique for P. monodon should be made as it is not well established compared to that of P. japonicus in Japan. The research programme on hatchery techniques on P. monodon lacks sustained support and coordination of efforts. Thus, the private sector has been left alone to hit-and-miss affair in their operations. The interest of the private sector is a healthy sign of willingness to take risks. However, capital resources are wasted if the operations do not succeed and the blame almost always go to the inefficiency of the government in providing the right technical assistance and guidance.

Hatchery operations require the following conditions to become successful:

1. Appropriate design of hatchery facility particularly with respect to quality of water and availability

2. Supply of healthy spawners

3. Experienced and knowledgeable technicians conversant with the behavior and feed requirement of shrimp larvae at certain stage of its life cycle

4. Availability of the appropriate type of feeds

Figure 4a. Fishing grounds of kuruma shrimp, Penaeus japonicus, in Hamana-ko Lagoon. Figures denote depth in m.
Source: Uno, 1985

In view of the different stages of larval development of the shrimp, specialization of production would perhaps be better to maximize the use of available skills and provide more efficiency in the chain of seed production. This situation has developed in Taiwan as well as in Thailand although in a different context. In Taiwan, several specialized sub-businesses related to shrimp seed production include: (a) spawner supplier; (b) nauplius producer; (c) nauplius broker; (d) early stage postlarvae producer (PL10–PL12); (e) late stage postlarvae producer (PL20–PL35); and (f) postlarvae (PL10–PL35) broker. Figure 5 illustrates the specialized sub-businesses of the prawn industry in Taiwan. A firm or family business enterprise raises its crop to a certain stage of maturity and. sell the crop to the customers with the skill and capacity to raise the larvae to the next higher level of maturity (Liao, 1987). This avoids a total failure of operation of a hatchery if the facility cannot completely produce shrimp postlarvae or juveniles for grow-out use. Specialization also strengthens the seed production base of the shrimp culture industry. This is seen in the Philippine milkfish fry industry where there are the fry gatherers, the brokers and the milkfish nursery operators.

In Thailand, on the other hand, specialization came about as a consequence of over-production of prawn fry resulting in very low prices. The existing hatchery facilities, particularly the backyard prawn hatcheries went into shrimp larvae rearing and live food organism culture. The prawn hatchery operators learned to diversify the use of their facilities for the production of shrimp and marine fish larvae such as P. monodon, P. merguiensis, seabass and grouper according to season and demand. At present there are over 800 backyard prawn hatcheries which specialize in nauplii, postlarvae and food organisms (Csavas, 1988).

Figure 5. Specialized sub-businesses in the Taiwanese prawn culture industry
Source: Liao, 1988

The same situation has not yet occurred in the Philippines. There are a number of hatchery facilities already lying idle due to failures in hatchery operations not because of overproduction but more on failure in design of hatchery facilities and the lack of skills in hatchery management.

For information on stages of the life history of P. monodon, Table 2 shows the duration in each stage. Figure 6 illustrates the larval stages of the shrimp.

The most difficult stage of the shrimp larvae is the transformation from zoea to mysis stages. Each stage of larval development requires different kind of food. Table 3 summarizes the kinds of food of shrimp larvae from zoea to postlarvae. The feeding regimes during the developmental stages of penaeid shrimp is illustrated in Figure 7.

Table 2. Life history phases of the giant tiger prawn, Penaeus monodon

¹Egg diameter
²Minimum size with jointed petasma
³Minimum size with adult-like thelycum
⁴Minimum size with spermatozoa in terminal ampoules
⁵Minimum size with spermatozoa with thelycum
⁶Maximum size ever found
Source: Motoh, 1985

Figure 6. Larval stages of Penaeus monodon A - lateral view; B - ventral view (Source: Motoh, 1985)

Table 3. Feed materials used for shrimp larval stages

NOTE: ++ Good;
+ Available;
- Poor
* Unknown - Origins presently being verified but cannot be substantiated at this time
Source: Liao, 1984

*Community culture method only
Solid lines (—) for most prominent feeding regime
Dashed lines (. . . . .) for occasional, less widely used regime

Figure 7. Schematic representation of feeding regimes for developmental stages of penaeid shrimp and related culture parameters
Source: Liao, 1984

Figure 8. Algae culture using natural light

For larval rearing of P. monodon, some of the essential aspects of postlarvae production based on Taiwan experience and conditions are summarized in Table 4.

Table 4. Some aspects concerning larvae rearing of Penaeus monodon in Taiwan

Source: Liao, 1984

Significant contributions of research to the shrimp hatchery industry has been done elsewhere, mostly in developed countries. These include the identification of nutritionally good species of algae and strains of Artemia as food organisms of shrimp larvae and the means by which the bio-chemical composition of algae, rotifers and Artemia may be enhanced by altering their nutrient source and rearing conditions. The development of a technique of disinfection and decapsulation of Artemia cyst during hatching has reduced fouling and contamination prior to hatching. The development of microencapsulated feeds for shrimp larvae is a breakthrough in hatchery technology (Wickins, 1986). The use of these imported feed materials are however, costly and small fish farmers are not able to procure them. Techniques of food organism culture have also been developed. Algae or zooplankton culture need not be indoors with sophisticated facilities. The use of plastic bags containing the culture media under a shed outdoors is not difficult to set up as shown in Figure 8. Asia is blessed with adequate sunlight the year round to promote algae culture.

A hatchery design should provide efficiency of water use and conveyance such as a ladder type of hatchery taking advantage of gravity system as shown in Figure 9. Engineering considerations for disease and stress prevention in shrimp hatcheries and grow-out ponds were studied by Gacutan and Vizcarra (1988) which are now being adapted in recent construction of shrimp hatcheries and pond renovations in the Philippines (Appendix 1).

There are three major sizes of hatcheries, namely; large, medium and small. The characteristics of such hatcheries are summarized in Table 5.

Most of the complaints of hatchery operators concern about low survival and disease infections. The low rate of survival may be due to eyestalk ablation. It has been reported that a maximum of 2–3 or 4–5 spawnings are obtained after each process of ablation. Consequently, the health conditions of larvae obtained from the later spawnings are claimed to be poorer than those obtained in earlier spawnings; shrimp larvae obtained from spawners by eyestalk ablation are weaker, hence, lower rates of survival than those obtained from spawners caught from the wild or non-ablated individuals. These observations, however, need confirmation through scientific research to determine the causes of low survival of larvae from ablated spawners (Liao, 1984).

Diseases often result to high losses of hatchery operators. Some of the common diseases encountered in shrimp hatcheries, the symptoms and treatment are summarized in Table 6.

Figure 9. A ladder system hatchery taking advantage of ground slope and water levels
Source: Liao, 1984

Table 5. Distinctive characteristics of three major sizes of hatcheries

Source: Liao, 1984

Table 6. Diseases found in the developmental stages of penaeid prawn larvae and their control methods

* N = nauplius; Z = zoea; M = mysis; and PL = post-larva