1Institute of Aquaculture, University of Stirling
Stirling, FK9 4LA, Stirling, UK
2Aquaculture and Aquatic Resource Management
Asian Institute of Technology
P.O. Box 4, Klong Luang
Pathum Thani 12120, Thailand
3Research Institute for Aquaculture No. 1
Dinh Bang, Tien Son, Bac Ninh, Vietnam
Little, D.C., P.A. Tuan and B. Barman. 2002. Health management issues in freshwater fish hatcheries, nurseries and fry distribution, with emphasis on experiences in Vietnam and Bangladesh. p. 141-146. In: J.R. Arthur, M.J. Phillips, R.P. Subasinghe, M.B. Reantaso and I.H. MacRae. (eds.) Primary Aquatic Animal Health Care in Rural, Small-scale, Aquaculture Development. FAO Fish. Tech. Pap. No. 406.
An understanding of the status of fish seed production and marketing in various countries in Asia informs any analysis of health management issues. Rapid development of the sector by small entrepreneurs over the last few decades, and its concentration at certain favourable locations, may have either positive or negative impacts on the health status of fish seed. Key factors likely to affect health status are identified for hatcheries, nurseries and traders. Decentralised seed production approaches have most potential for minimising health management problems.
Freshwater fish seed supply in Asia is largely based on networks of small entrepreneurs that produce and deliver seed to farmers for stocking in ponds and ricefields. Most food-fish culture in the region remains semi-intensive, and farmers consider health issues to be relatively unimportant. In contrast, seed production is typically intensive, and health management of both brood and seed fish can be critical. Understanding people and their motivations within these networks is important if these health issues are to be tackled.
Sustainable rural aquaculture requires timely delivered, high-quality seed; the performance of food fish is related to both the quality of seed and their management post-stocking. Most seed used by smallholders is produced and delivered by the private sector, conservatively more than 90% in countries such as Bangladesh and Vietnam. Increasingly, as the quantity and availability of fish seed have improved, the quality has been questioned. Factors affecting the health status of fish seed available to farmers are complex and relate to both the knowledge of the various "actors" in seed networks and the broader environment, both physical and economic.
In areas where it developed in response to local demand, traditional aquaculture was based on wild seed. Current centres of seed production are often former sites of wild seed nursing and distribution. Typically, they are close to large rivers, from which hatchlings and fry were harvested, and to railways and, increasingly, roads that have facilitated their distribution. More recently, as the importance of seed availability in promoting aquaculture has become better appreciated, these centres have become nodes of demonstration and extension.
The modern hatchery sector in both Vietnam and Bangladesh is less than 30 years old, but is characterised by increasing levels of competition, declining prices and increasing diversification and specialisation. While an increased choice of species for rural farmers is beneficial, these production trends can negatively affect the quality of seed.
The delivery of fish seed to farmers is preceded by their production and transfer through a network of "actors" responsible for different stages and processes. Fish, both brood and seed, are moved around using a variety of methods including motor vehicles e.g., trucks and motorcycles, and human power (bicycles and on-foot). Earthen ponds remain the main type of production unit, but tanks, usually brick or concrete, and cages, especially fine-mesh hapas, are important in the production and marketing of fish seed.
The human element of networks includes producers, final customers and traders of various types. The inputs required for producing fish seed are specialised and, where production is well established and concentrated, a range of service providers usually develops. These include people specialising in supplying hormones, especially pituitary glands, chemicals, feeds, cloth and small items of equipment. Harvest and transportation of seed and broodfish often also becomes a speciality, partly because of the necessary skills and equipment required. Enterprise "clusters" are typical for both hatchling and nursed-seed production, such as in Jessore and Bogra in Bangladesh; Gong Nam in Nong Khai Province, Thailand; and Hai Hung Province in Vietnam. In Bangladesh and Vietnam, separate, specialised producers carry out production of hatchlings and nursed fry. These may occur in distinct and separate locations, as different resources are required.
Broodfish are typically both held by the hatchery operator and purchased as required, depending on the species, size of hatchery and demand. The open nature of broodfish supply generally results in frequent transfers and mixing of different batches of fish, with consequences for genetic quality and the transfer of pathogens.
A major issue is the determination of whether underlying cause and level of losses in fish seed, which occur at each stage of production and delivery within networks, have any impact on their subsequent performance as food fish after purchase and stocking. In practical terms, poor management post-stocking could obscure real variation in fish seed quality.
The major components of management and environment that impact on health outcomes for fish include water quality, nutrition and the degree and quality of handling. The nature of fish-seed supply networks predisposes fish to disease. Handling of both brood and seed fish typically occurs frequently and in environments prone to change and extremes. This increases stress on fish and the likelihood of infection and disease. Moreover, declining profit margins encourage practices that increase seed output for a given level of resources (space, water, feed, labour) that exacerbate these problems. These trends towards more intensive practices, if not accompanied by improved management, may further affect the pathogen-fish balance, increasing the prevalence of disease.
Management of broodstock has critical impacts on the health status and subsequent performance of seed. A trend towards commercial hatcheries outsourcing broodfish has consequences for both genetic quality and the movement of pathogens. Broodfish management of this type entails little risk of inbreeding occurring provided that the genetic variation of initial stocks is sufficiently high.
Husbandry of broodstock, particularly during maturation of the gonads, is also likely to affect seed quality. Transportation and immediate induced ovulation of female Clarias macrocephalus have been shown to reduce the quality of hatchlings when compared to seed from broodfish maintained and matured in the hatchery (Ingthamjitr 1997). A trend in northern Vietnam, and elsewhere in the region, towards increasing carp broodstock density, for economic reasons, prior to induced spawning could also negatively affect seed quality (RIA 1/AIT 1999). Other factors identified by hatchery operators that might affect seed quality include increased frequency of spawning and out-of-season production, both of which may increase stress on broodfish and/or result in production of seed from immature gametes.
Induced spawning techniques themselves have also been associated with variable quality seed. Food-fish farmers in northern Vietnam believe that seed produced using pituitary glands are stronger than seed produced using LH-RH analogues and dopamine antagonists and are prepared to pay more for the pituitary glands. A recent field trial indicated that different hormone types can impact on the numbers and quality of seed produced (Pham et al. 1999). Handling stress associated with stripping gametes is known to reduce survival of broodfish, and natural spawning, where possible, is often preferred for this reason.
Collection and incubation of seed can result in high losses through poor design and management. Mixed batches of seed produced from multiple and small-batch spawners, such as tilapia and gourami, increase problems of cross infection by pathogens and competition/cannibalism between fish of different age classes.
Poor design of spawning and incubation systems, such as catfish (Clarias} egg collecting trays that do not allow efficient separation of hatchlings from eggs, and tilapia incubators that mechanically traumatise eggs, result in poor survival. Secondary fungal infections that follow primary bacterial disease or direct injury-related mortality are common in such systems. Effects on the quality of surviving seed have, however, not been quantified.
Maintaining good water quality throughout the spawning and incubation cycle is critical if hatcheries are to reduce losses due to pathogens, however, water shortages and costs have forced hatcheries throughout the region to innovate. Carp hatcheries in Bangladesh have increased the efficiency of hatchling production/volume of water by using antiseptics during incubation. This is partly because reduced profit margins over the last decade have stimulated operators to use more surface water rather than ground water, which is costlier to pump. In Bangladesh and Vietnam, where use of surface water is the norm, hatcheries use floating aquatic macrophytes to moderate water temperatures and reduce the level of suspended solids in hatchery water.
Production of carp fry and fingerlings in earthen ponds is the standard system throughout Asia. The key design features, in terms of enhancing survival and quality of the seed produced, are the availability of water and the ability to drain such ponds. Ponds that can be cost-effectively drained, rapidly and completely, will encourage sound management that maintains water quality and natural feed levels and prevents accumulation of predators and pathogens. Close proximity of large numbers of nursery operations or "clusters," as with any aquaculture system, can result in greater likelihood of pathogen transfer and poor water quality.
The trading of fish seed, as with other perishable commodities, imposes high risks on those involved. Minimum holding times benefit the individuals and organisations involved, and experience is quickly developed to "make the sale," rather than prevent deterioration in condition of the product per se. Often, especially as customers become more knowledgeable, these factors can become interdependent. In practice, itinerant vendors are the main suppliers of seed in the region, and farmers may have little experience in selecting high quality seed. The level of choice (i.e., the number of vendors that visit during any given season) varies dramatically, however, even within the same region.
There are many practical difficulties in maintaining fish seed in good condition. High ambient temperatures, long marketing chains and basic physical facilities are important constraints. Traders selling fish seed from fixed outlets at the same location have many advantages in maintaining fish-seed quality, as electricity and clean water may be accessed more easily.
Closed transportation, based on polythene bags inflated with oxygen, can improve quality, but will also impose limitations. Generally, motorised vehicles are required, and the amounts that can be transported are reduced; this increases the costs of seed transportation compared to open systems using aeration/oxygenation.
The production and marketing of fish seed is increasingly characterised by concentrations of operations clustered closely together. Although this is typical of specialised small businesses in Asia, the phenomenon can have both positive and negative impacts on the quality of such a perishable commodity as fish seed.
Close proximity of sales outlets can allow knowledgeable customers to select for quality and price, increasing pressure on vendors to maintain quality. It can also encourage better information exchange and rapid dissemination of improved techniques and practice. Clusters of enterprises are also characterised by specialisation in knowledge and activity that can enhance consistency and quality of fish seed. These include specialists in pituitary gland extraction and preservation, harvesting of earthen ponds, management of incubation, selection and inducement of breeding fish etc. The availability of materials and equipment (e.g., pumps, nets and chemicals) that are otherwise scarce or expensive is also typically improved.
Fish-seed health can also be negatively affected in clusters of nursing operations through reduction in local water quality caused by pond effluents. Nursery ponds have shorter production cycles and are typically emptied and refilled more often than foodfish-producing units. The greater competition among neighbouring nursery operations can also lead to reduced profitability and investment, especially in terms of pond preparation and feeding. Perhaps most importantly, clusters of nursing enterprises inevitably result in long-distance marketing of fry and concomitant risks of transport stress and damage.
The high fecundity of most cultured fish species means that even extensive seed production may suffice to meet local needs, especially when demand is highly seasonal. Temporary environments, such as ricefields and simple hapas suspended in water bodies can be used to produce large fish seed for the beginning of the main culture season. Such an approach has advantages in terms of low entry costs for poor farmers to move to seed production, and important consequences for quality, since seed needs to be distributed only over short distances. The likelihood of transport-induced stress and trauma is highly related to distance and duration of transportation. Pest and pathogen build-up and the need to use chemotherapeutants are also less likely with such seasonal, extensive practices. Local production of tilapias and small carps that are easy to breed has proved particularly successful. The potential constraints to basing fish seed supply on small, isolated breeding populations should be understood and counteracted. Development agents, whether government, non-government or commercial, could have important roles in overcoming such constraints. Knowledge of the issues and action by farmer-producers themselves as individuals or groups may ultimately be more important, however.
Promotion of decentralised seed supply runs counter to the specialisation and centralisation of seed production occurring in both Vietnam and Bangladesh. Indeed, the economies of scale, specialised knowledge and overall relative advantage of such clusters of seed production have been a major force for promotion of aquaculture in both countries. Promoting, within seed supply networks, appropriate technologies and methods for local people, can improve availability and quality of fish seed and improve the livelihoods of seed-producing farmers and their customers.
Much of the financial support towards understanding the freshwater fish seed sector in Asia was provided by the Department for International Development, UK (DFID), including the current research grant from the Aquaculture Research Programme, Fish Seed Quality in Asia.
Ingthamjitr, S. 1997. Hybrid catfish Clarias catfish seed production and marketing in Central Thailand and experimental testing of seed quality. Ph.D. Dissertation, Asian Institute of Technology, Bangkok, 135 p.
Pham, T.A, D.C. Little, A.M. MacNiven and N.H. Nguyen. 1999. Preliminary investigation into performance of mrigal (Cirrhinus mrigala) seed produced by using LHRH-a and carp pituitary gland extract. Working Paper 1. Fish Seed Quality in Asia Project, Asian Institute of Technology, Pathum Thani, 7 p.
RIA 1/AIT. 1999. Fish Seed Quality in Northern Vietnam. State of the System
Report. Research Institute for Aquaculture 1/Asian Institute for Aquaculture,
Pathum Thani, 23 p.