October-December 2003 (Vol. VIII No. 4) 23 Tilapia seed production in Ho Chi Minh City, Southern Vietnam H. P. V. Huy, A. MacNiven, N. V. Tu, Ram C. Bhujel and David C. Little method of seed production. Perceptions of seed quality vary with grow-out farmers, traders and nursers. Inconsistent tilapia seed quality was perceived to be a problem by the traders in Southern Vietnam, especially those distributing seed to the Mekong Delta that involves longer transportation times. Farmers were also of the opinion that the poor seed quality is a main factor causing poor fish productivity. The causes of the perceived poor quality could be due to poor pond management, lack of technical know-how, long distance transportation, poor handling and/or poor broodstock quality. Therefore, tilapia fry were collected for an on- station research at the University of Agriculture and Forestry to compare the quality and to identify the associated factors. A survey was also conducted to provide supplementary information to the research trial. It was felt that this information on it’s own would be useful for those who are involved in planning, research and education in Vietnam and other parts of the world. Survey method A questionnaire survey was conducted with 20 fry producers who provided seed that were used in an on-station nursery trial. These farmers represented a sample of about 10% of the hatchery operators in District no. 8 of Ho Chi Minh City A brief face-to- face interview was carried out with each hatchery operator to gather information on the source of seed, broodstock and nursery management. The survey covered both socio- economic and technical issues relating to the quality of fish seed. Production system and the practices Observation during the survey revealed that most farmers use at least two ponds that are filled with water from the municipal sewage canals, which pass through the district. Before filling the ponds, farmers drain and dry them, and use pesticides to kill predators. Some farmers also use quick lime (@7-10 kg/100m2). The average pond size ranges from 1,000 to 2,000 m2. As sewage water is rich in nutrients, growth of natural food or plankton occurs within a week or so. Sewage varies in strength seasonally. As it is stronger in the dry season, it needs settlement before use. After the appearance of sufficient natural food, tilapia brooders are stocked into the pond i.e. Pond 1 (Figure 1). Normally fry are observed after about three weeks of broodfish stocking. After spawning the broodstock are transferred to the other pond i.e. Pond 2 leaving the fry behind in the Pond 1. Some farmers claim that if broodfish are seined by 4-5 persons early in the morning when the fish are surfacing because of low dissolved oxygen, 90% of the broodfish can be removed. All the fingerlings are harvested after about 10-30 days by seining and draining of the pond. The seed are graded at harvest into 5 sizes (mean individual weights 6, 8, 10, 12 and 14 g) and the ratio of seed size harvested depends on the nursing period. The duration of cycles varies with demand. If the demand is low the operator tends to lengthen the nursing period resulting in larger seed. The first pond is again prepared over a 10-day period for the next breeding cycle to stock the same broodfish kept in the second pond or the new breeders. The new breeders are the fingerlings produced in these ponds and nursed separately in other ponds. In this way the cycle of tilapia seed production continues. The majority of seed producers use 3-4 Climatic conditions in Vietnam vary greatly as the country stretches from the South of China in the North to the Gulf of Thailand in the South. In the north, temperatures sometimes drop below 10ºC during winter, and tilapias need careful over-wintering to survive. In the south of the country temperatures are suitable year-round. In Southern Vietnam especially around Ho Chi Minh (HCM) city, tilapia seed is produced in sewage-fed ponds using methods that have been developed by farmers themselves. The majority of tilapia seed used in the provinces around HCM and on the Mekong Delta are produced in these systems. Tilapia seed production has become a part of diversified suburban agriculture system and appears to have evolved as a byproduct of food-fish production. Culture of fish in ponds fed with wastes from latrines has been a tradition in Southern Vietnam, especially stocking of Pangasius seed collected from wild. Stocking of hatchery-produced seed is more recent phenomenon that has been driven by the market demand in and around the HCM city where aquaculture is increasingly commercial in nature; 40% of the fish farmers say that aquaculture is their main source of income1. Although Chinese and Indian carps, silver barb, gouramies and hybrid catfish are cultured in Southern Vietnam, the most preferred species are tilapia and the common carp. Hatchery techniques and infrastructures for all of these species are now well developed. Specialized nursing and trading activities have become well established. Both wholesalers and retailers are important players in the trading of fish seed in Southern Vietnam. While this has improved the supply of fish seed to farmers, it has led to a lack of contact and reduced information flow between hatchery operators and food fish farmers. For example food fish farmers understand little about the source of broodfish or