WP/81/SPH/CP-19

STATUS OF SMALL-SCALE MACROBRACHIUM HATCHERIES IN THAILAND

by

Somsuk Singholka¹

1. INTRODUCTION

Macrobrachium early research in Thailand has not received international recognition because it was mainly published in Thai language, with few English summaries. The works on larvae, pond and net culture has been documented by Tongsangsa in 1965, Bhromanonda and Sahavacharin in 1967, Pongsuwanna in 1967, Sidthimunka and Chaopaknam in 1966, and Batsanchai in 1970.

In 1976, the work was transferred to the new Fisheries research station at Chachoengsao province, which was built on the firm foundation of earlier work elsewhere in Thailand. Macrobrachium farming in Thailand is now on a larger scale.

2. HATCHERY PRODUCTION

Currently, there are two government funded fresh-water prawn hatcheries in Thailand. Postlarvae is still produced in the far south at Songkhla Fisheries Station in an intermittent basis, mainly for stocking in the ponds located at the brackishwater portion of Songkhla lake and also in the ponds in the surrounding areas. A little over 1.1 million postlarvae of Macrobrachium have been produced at this station since 1970. However, the major thrust in stimulating the expansion of freshwater prawn farming in Thailand centres on the Chachongsao Fisheries Station, situated some 70 km east of Bangkok. This station is unique in Thailand in being solely devoted to the production and distribution of postlarvae of one species (Macrobrachium) throughout the country and with training and extension work in larval and postlarval rearing. The high level of interest in the work at this fisheries station can be gauged by the fact that the number of the visitors it received in organized parties alone currently exceed 10 000 per year. In addition to government hatcheries (3), the number of the small backyard hatcheries has grown to 31 and there are currently 10 large commercial hatcheries. The estimated current and potential output of these hatcheries are summarized in Table 1. Current potential output exceeds 80 million postlarvae per year from existing hatcheries.

All the hatcheries, except Songkhla and ADB project hatcheries are not farther than 150 km from Bangkok, mostly on the east and southeast. Most of the backyard hatcheries are located inland rather than in coastal areas. Postlarvae from private hatcheries are transported by road, rail and air throughout Thailand. Normally, long road journeys will be made overnight, sometime for distance as far as 800 km. Inflated plastic bags containing water are invariably used; the Chachoengsao Fisheries Station has developed a system used on long travel which stacks plastic bags containing postlarvae on shelves in a closed truck, temperature being kept low by blowing air over ice cubes by means of the battery operated fan. This station has, since its first full year of operation (1977) distributed over 25 million juveniles to farmers by November 1981, and has placed over 3 million in natural waters. Production from this station is expected to be 20 million per year within 2 years.

The existence of at least 44 Macrobrachium hatcheries in Thailand means, almost by definition, that at least 44 different larval rearing technique are used; some generalizations are possible. The clearwater technique is invariably employed although some hatcheries previously used green water. A salinity of 12 ppt sometime reduced gradually before and after metamorphosis, is used with water changes after the first ten larval rearing days varying from 10–50 percent daily, depending on the availability of seawater. A wide range of larval feeds are used, including Artemia nauplii and prepared feed consisting of mussel flesh, fish flesh whole egg custard, egg yolk custard and soybean curd, alone or in combination. One backyard hatchery maintains its larvae entirely on a diet of Moina sp.

¹ Chief, (Macrobrachium Research Center)
Chachoengsao Fisheries Station, Department of Fisheries, Bangpakong, Chachoengsao, Thailand

The high cost of importing brine shrimp cyst is likely to be reduced in the future in Thailand, now that local inoculation of Artemia in solar salt ponds are successfully producing Thai Artemia cysts. The number of days of metamorphosis for Thai freshwater prawn hatcheries varies widely but each batch of larvae is normally completed within one month.

Some berried female prawns are obtained from natural waters but most of the larger hatcheries either maintain their own broodstock or draw from the ponds of farmers which they have previously stocked with juveniles. The easy availability of barried females has enabled hatcheries to concentrate more on maximizing survival rate. It is estimated that average survival rate of 10–50 percent are achieved in private hatcheries and 30–50 percent at the Chachoengsao Fisheries Station. The containers used for larval culture are varied. Most custom-made tanks are concrete which is cheaper in Thailand than plastic. Many other containers are used, however, including modified concrete drainage pipes and earthen ware jars used for domestic water storage. Water depths of 75 cm are normally used but some hatcheries economize on water consumption and labour by using a water depth of only 25 cm.

The backyard hatcheries are mostly run as part-time occupation and, in any case, normally employ family labour only. The highest operational cost of inland backyard hatchery is Artemia cyst, and also seawater which is sometimes bought from suppliers. Most back-yard hatcheries use canal water or tap water as their source of freshwater. The larger hatcheries mostly use well water.

The cost of constructing a family-run hatchery for Macrobrachium obviously depends on its size but many start up with capital expenditure of as low as US $ 2000. At the upper end of the scale, the largest commercial freshwater prawn hatchery existing in Thailand in 1979, which complied with the highest international standards of hatchery construction and had a potential output of 30 million postlarvae per year required a total capital input of US $ 500 000. This hatchery employs a manager, three biologists and a number of workers, with a total labour cost estimated at about US $ 27 000 annually. This hatchery has since been sold by its owners and the original owners have since constructed another, less elaborate hatchery closer to their production farms.

Postlarvae from government hatcheries was originally distributed free for stocks within 2–3 weeks of metamorphosis and it has been this policy which has encouraged the rapid growth of Macrobrachium farming in Thailand. The price of US $ 12.50/1 000 juveniles is now being applied selectively to those farmers who are identified as able to pay. The freshwater prawn juveniles sold by private hatcheries in 1979 varied from US $ 17–37/1 000 juveniles depending on profit margins and on the age of the juveniles sold. Many small hatcheries allow the juveniles to remain in the nursery tanks for up to one month after metamorphosis. This commercial value of freshwater prawn juveniles in Thailand has since decreased down to US $ 12.50/1 000 juveniles and are therefore cheaper for the farmers to buy rather than produce them.

As in freshwater prawn hatcheries in other countries, the problems to be considered in prawn larvae rearing centers around: site selection, water supply, and management. Predation has been observed and mortalities occur without the specific causes being detected. The principal cause of such losses is often human mistake. According to site, the reliability and quality of both freshwater and seawater should be considered. Although the large government and private hatcheries treat incoming water by sedimentation, filtration and chemical treatment, the smaller units generally use raw, simply screened water. Improvement in water quality using simple and cheap techniques has recently been used at Chachoengsao Fisheries Station and methods of surveying new sites to detect the suitability of installing natural filters has been demonstrated as explained by Cansdale in 1979. One commercial hatchery now uses the technique, and a modification of the “Cansdale” shallow beach screen well, made possible by the near-perfect beach structure is in use at another.

3. THE FUTURE

Technical improvement and business growth of Macrobrachium in Thailand is proceeding well. A comprehensive extension programme for farmers and fisheries officers is being run by Chachoengsao Fisheries Station to improve hatchery and pond rearing technique. Research on Artemia cyst production, freshwater prawn nutrition and recirculation systems to reduce water consumption in hatcheries is carried out at this station. Facilities at the Chachoengsao Fisheries Station are being improved so that the potential production rate of 20 million PL per year can be achieved.

The government seeks to stimulate an increase in the total production of postlarvae of Macrobrachium in Thailand to 250 million/year within 5 years. This output, at present stocking levels and production rates, would be sufficient to raise production of farmed freshwater prawn in Thailand to over 4 000 tons/year.

Table 1.
Estimated output of juvenile Macrobrachium rosenbergii from hatcheries in Thailand