8. Stock-enhancement in small and medium-sized inland waterbodies

The area of small waterbodies (those with water area <400 ha) in the region is estimated to be 66 710 052 ha (FAO 1999). The great majority of these waterbodies are man-made, except perhaps the oxbow lakes (locally known as baors) in Bangladesh. These waterbodies are typically constructed for irrigation purposes, supplying water for downstream agricultural activities such as rice-paddy cultivation and often depend on relatively small catchments for water. The management of these small waterbodies usually comes under the purview of a government authority such as Agrarian Services (Sri Lanka) and/or a division (e.g. Irrigation Department) of the agricultural services (e.g. Thailand, Lao PDR etc.). Day to day management of the water resources is carried out by the competent government agency, often in collaboration with government-approved farmer organizations comprised primarily of the downstream farming communities. Such organizations have various names and can be collectively referred to as "water user groups". Perhaps one of the few exceptions in the region are the leased floodplain fisheries in Myanmar, where large areas of the floodplain are effectively almost perennial waterbodies and can be quite large (up to about 600 ha). These waterbodies fall under the purview of the fisheries authorities of the government and the local authority, which determines the leasing arrangements. In PR China, each waterbody is managed by a Reservoir Bureau, with subcomponents for catchment, downstream and fishery management. In Viet Nam, small waterbodies come under the purview of the provincial government authorities, such as the agriculture and rural development departments of the provincial government. These waterbodies are leased to individuals or groups of individuals for varying periods of time, for conducting fishery activities.

Small waterbodies have very different characteristics to those considered in the previous section, and the major differences are listed in Table 26. The natural fish recruitment and production of small waterbodies are usually is too low to support any substantial fishery. Because of its small size, the waterbody has few habitats that cannot be easily fished, and thus while the productivity of the waterbody might be quite good, the natural fish population is quite vulnerable to over-fishing. Fisheries development in small waterbodies is therefore usually done in conjunction with a regular stock enhancement programme.

Small waterbodies also tend to be managed by individuals and/or organized groups of individuals who determine access and fishing effort and in some cases, implement some form of stock enhancement. These groups also tend to have some form of direct or indirect ownership of the stocked fish that may or may not have some form of official recognition. This range of features is quite different to the situation found in the open-access fisheries of large waterbodies, and they are, in fact, features more akin to the definition of aquaculture. These forms of management practice are commonly referred to as "culturebased fisheries" (FAO 1997, De Silva 2003) or "aquaculture-based fisheries" (Lorenzen 2003).^[5]

The scope for fisheries development in small waterbodies (i.e. culture-based fisheries development) is widely recognized (Welcomme and Bartley 1998; De Silva 2000, 2003; Lorenzen et al. 2001) to have one of the highest potentials to increase food fish production in Asia in the near future. Such developments have added benefits to most communities, and foremost of these are:

• providing an affordable source of fresh animal protein;

• contributing significantly to rural household and farmer income;

• encouraging multiple and non-consumptive use of a primary resource - water, with little foreseeable negative influence(s) on the traditional use of the resource by the community;

• creating synergies that result from a communal activity, with relatively undefinable and unquantifiable but often positive influences on the immediate community;

• being relatively less resource intensive and needing little capital expenditure as compared to most forms of aquaculture; and

• opening up of new opportunities for some sectors of the community as a direct result of culturebased fishery development.

Table 26. A comparison of the principal, general characteristics of small and large inland waterbodies

Fishery development in small inland waterbodies shares many common features of pond aquaculture:

• the environment is relatively easy to manipulate;

• the waterbody can be prepared so that almost all the stock is what was seeded (through removal of "wild fish" prior to stocking);

• seed stock can be based on potential consumer acceptability and marketability;

• all stock is harvestable, and partial or staggered harvesting can be carried out to suit market demands; and

• the natural productivity can be enhanced through fertilization (if commercially viable).

In general, the greatest difference between pond culture and culture-based fisheries is that the latter is a secondary user of the water resource and rarely needs supplementary feed input (with the possible exception of grass when grass carp is stocked), relying instead on natural productivity and/or fertilization.

8.1 Stock enhancement and/or culture-based fisheries in Asia

Considering the diverse opportunities and potential within the Asian region, it is perhaps surprising that, with the exception of PR China, culture-based fisheries have only received attention in most countries in the last 20 years. The possible reasons for this are that:

• Pressure on aquatic food resources began to occur only two to three decades ago.

• Culture-based fisheries were dependent on limited wild sources of seed stocks and were in competition with aquaculture for that supply.

• Artificial propagation of stocked species has only recently become a widely available technique.

• Waterbodies suitable for culture-based fisheries were under the purview of non-fisheries related state authorities.

• Farming communities who used the water resource had little interest or skill in culture-based fisheries.

• A relatively recent realization at the policy level, of the potential of culture-based fisheries has led to the consequent provision of relevant state mechanisms to support development, including the introduction of required legislative changes, provision of institutional structures etc.

Most developing countries in Asia that have suitable water resources now acknowledge the potential of culture-based fisheries to contribute significantly to foodfish supplies, particularly among the rural poor. The latter group is the immediate beneficiary of such activities by virtue of the fact that most of the water resources suitable for culture-based fisheries are invariably located in rural areas.

There has been quite a significant amount of research targeted at culture-based fisheries in Asia over the past two decades (see, for example, Thyaparan 1982; Lorenzen 1995, 2003; Middendorp et al. 1996; Lorenzen et al. 1998; Nguyen et al. 2001; De Silva 2003), and this review will not cover individual country practices (Plates 19, 20, 21). The common features of culture-based fisheries are that they tend to be communal activities and are mostly village based. The yield from culture-based fisheries far exceeds that from other larger, inland waterbodies (Middendorp et al. 1996, Lorenzen et al. 1998, Nguyen et al. 2001), and in certain instances, even that from semi-intensive pondfish culture. Perhaps the greatest strides in culture-based fisheries have been made in PR China, where the yield increased from about 50 000 to 1 million tonnes in the period 1980-1997, with a concurrent increase in yield from about 80 to 763 kg/ha/yr (Song 1999).

Li (1988, 1992) and Li and Xu (1995) described the culture-based fishery practices in PR China, where over a number of years of trial and error, general guidelines for maximizing production from culturebased fisheries have been empirically determined. Foremost among these is the stocking size and preparation of the waterbody prior to stocking. In China, the average stocking size is 27 g (12-14 cm seed), and in small and medium-sized waterbodies, predators are removed prior to stocking. A more recent development in culture-based fisheries is to retain, depending on the nature of the waterbody and the prevailing prices, high-valued, small predatory species such as clearhead icefish (Protosalanx hyalocranius) and indeed, such species may be introduced to increase the value of the yield (Liu and Yongchuan 1998). The Chinese culture-based fishery is based on using standard species combinations and stocking densities that are calculated from the productivity of each reservoir (Table 27). Another notable factor contributing to the relatively high yields is that fishery activities were taken into account during the planning stages of Chinese reservoir construction. This included designs that minimize the number of escapees and facilitate harvesting.

Table 27. Data depicting the relationship of stocking combinations and mean yield to reservoir trophic status and size, in culture-based fisheries in PR China (modified from De Silva 2003; original data based on Li and Xi 1995)

¹ Bh - bighead carp, Sc - silver carp, Gc - grass carp, Wf - wuchang fish; Cc - Common carp, Mc - mud carp.

Based on an estimated area of 66 710 052 ha of small waterbodies in the Asian region (FAO 1999), De Silva (2003) predicted that even if only 15 percent of the total area was under culture-based fisheries using the best practices of the Chinese, this would translate into a potential fish yield of 2.5 million tonnes/yr. This may not be an unrealistic estimation in view of the increasing emphasis by governments on culture-based fisheries development in the region and the accompanying changes that are being introduced to improve institutional structures to make them a success. As the management of culture-based fishery activities is mostly at the community level, their success depends, to a significant extent, on having the appropriate and functional village institutional structures in place (Lorenzen et al. 1998).

8.2 Constraints to culture-based fishery development

As indicated earlier, with the exception of PR China, culture-based fisheries is a relatively new development in many Asian countries. This means that the technical, management and socio-economic aspects are still in a process of development. It is possible to identify a number of common constraints that affect most countries that must be addressed if culture-based fisheries are to be developed to any significant degree.

8.2.1 Species combinations and stocking ratios

One of the main constraints in optimizing yields from culture-based fisheries in most countries is the lack of knowledge on the most appropriate species combinations that should be used. Use of ad hoc species combinations and stocking densities can lead to reduction in yield, as well as the production of under-sized fish, resulting in low economic return. The waterbodies suitable for culture-based fishery activities differ widely in their morphology, catchment features and hydrological regimes and consequently, in their biological productivity. The final yield from a waterbody will depend not only on the species stocked and their size at stocking, but also on the biological productivity of the waterbody, which determines the food availability to the stocked seed, and hence their growth and well being. The success seen in PR China is based on the adoption of stocking strategies that have been worked out to suit the productivity of each waterbody (Table 27). A comparable method based on Secchi depth has been developed for oxbow lake fisheries in Bangladesh (Hasan et al. 1999).

The final strategy is based on the relationship of productivity (Y = fish yield in kg/ha) to stocking density (SD = number/ha) and Secchi depth (X = cm), which are:

Y = 811 - 3.18 X, and
Y = 15.88 + 0.184SD.

Examples of stocking densities and related species combinations for two oxbow lakes of different productivity suggested by this model are given in Table 28.

The empirical models used in Bangladesh and PR China provide an opportunity for the improved planning of enhancement activities that would not only lead to a cost saving on seed stock, but also to increases in fish yield.

Table 28. The suggested stocking ratio for culture-based fisheries in two oxbow lakes of different productivity (based on Secchi depth). Compiled from data from Hasan et al. (1999)

8.2.2 Seed supplies

Problems of seed supplies are not restricted to quantity and quality. Culture-based fisheries are often a secondary activity that is typically conducted in small non-perennial waterbodies. The timing of the supply of seed for stocking is crucial, and availability has to coincide with the filling of these waterbodies with the onset of rains. De Silva (1988) pointed out that the failure of the culture-based fishery development programme in Sri Lanka in the early 1980s was primarily due to the lack of availability of suitably sized fish at the correct time. The problem tends to be further exacerbated in most countries, as the main species used in the programmes (Chinese and Indian major carps) are often artificially propagated only once a year, typically at the onset of the monsoon season. This means that the fingerlings are too small to stock, and by the time they have been nursed, the water in small, nonperennial waterbodies is already depleted. The spawning of Chinese and Indian carps several months prior to the rainy season is possible, as well as multiple spawnings; however, this is more complicated and would not become mainstream practice unless there was high demand.

8.2.3 Management structures/institutions

Successful culture-based fisheries are dependent upon functional management structures, and these require a supporting institutional environment.

In Bangladesh, for example, the culture-based fisheries are in oxbow lakes that are under the purview of the Department of Fisheries and are managed by the stakeholders, a system that is referred to as a common property regime (CPR). Apu et al. (1999) observed that such a CPR can be sustained only through fostering cooperation among stakeholders (fishers), by providing incentives, maintaining equity, and ensuring democratic rotation of leadership and the monitoring all operations by the fishers themselves. These authors also observed that long-term security of tenure of the fishing rights for the CPR, as well as the long-term tenure of individual fishers in the CPR, were important determinants of sustainability.

Felsing et al. (2003) pointed out that in India, the current institutional context provides only limited incentive or support for aquaculture initiatives appropriate for resource-poor farmers, such as culture-based fisheries in non-perennial waterbodies in rural areas. These authors noted that the governmental emphasis is on capital intensive aquaculture technologies suitable for wealthier farmers, and that this emphasis has a bearing on the availability of credit, waterbody usage etc. They concluded that existing policies would hamper culture-based fisheries development or at least fail to provide the necessary momentum needed for the practices to flourish.

In Sri Lanka, the waterbodies used for culture-based fisheries are already under the management of the Village Cultivation/Farmers’ Committee (VCC) (drawn from among the downstream farming community), under the overall purview of the Department of Agrarian Services. Government bodies associated with fisheries development have no authority over these waterbodies. Culture-based fisheries in small, nonperennial waterbodies could therefore be developed only through the involvement of interested parties of the VCC, functioning as a Fishery Subcommittee of the VCC, thereby ensuring harmony among the major users of the water resource. Pushpalatha (2001) discussed the importance of the involvement of the farming community in culture-based fishery development and the need to train the farmers in the practices per se prior to investing in development.

8.2.4 Harvesting and marketing

The main harvesting period for most culture-based fisheries in the region is dictated primarily by the water regime in these non-perennial waterbodies, harvesting being done as the waterbody dries up. In general, this means that in a given area there will be simultaneous harvesting in many such waterbodies, often leading to an excess supply within a very short time frame and leading to a reduction in farm-gate price. The situation is further exacerbated because the great bulk of culture-based fisheries in the region are conducted in rural areas of low population density, where marketing channels are often not well developed. In most countries in Asia, with the possible exception of PR China, culture-based fishery activities are taken up by traditional agricultural farmers, as a subsidiary activity, and it is important that these activities result in a net economic gain to maintain farmer interest and hence, long-term viability. Therefore, the need to address the above issue is crucial.

There is very little information available on post-harvest technology for the species commonly used in culture-based fisheries, as well as on consumer acceptability of such products. Perhaps this is an area that warrants further investigation. Development of simple processing techniques such as sun drying of suitable species may be one avenue of ensuring a reasonable return to the producers.

Another plausible solution to preventing an over supply of fish in a given area may be to introduce staggered harvesting as the dry season approaches. Such an approach could be advantageous in two ways: firstly, by preventing an over supply within a narrow time frame and secondly, by increasing yields as a consequence of removal of the larger cohorts from the population. However, this strategy requires training of the communities involved on methods of partial harvesting, i.e. techniques for using a selective gear such as gillnets, ready access to such gear, and the rationale for adopting such a strategy. Adoption of this strategy should be preceded by relevant research, as information in this regard is not presently available.

8.3 Fingerling production for stock enhancement

The availability of fingerlings of appropriate size and species remains one of the major constraints to all forms of stock enhancement practices in most Asian countries. In most countries, often the priority is to fulfil the fingerling requirements for intensive aquaculture operations, and consequently and more often than not, the requirements for stock enhancement practices fall behind. It is also difficult to separate the availability of supplies for stock enhancement from that for aquaculture per se. Indeed, the problems of availability of seed stock and its quality have not received the attention that they rightly deserve from governments and researchers.

Technically, artificial propagation of the bulk of the species used in stock enhancement practices in Asia has been successful. Perhaps one of the improvements needed is to develop techniques for routine multiple spawnings in a year, ensuring a year-round supply of seed stock. Only the year-round availability of seed stock will ensure that most waterbodies, particularly the non-perennial ones, can be stocked at the proper time, so that the whole culture period can be effectively used by the stock. As previously discussed, one of the reasons for the failure of the culture-based fisheries programme in Sri Lanka in the 1980s was incorrect timing between seed availability and the filling of waterbodies (De Silva 1988).

In most Asian countries, backyard hatcheries are common, particularly for the propagation of Chinese and Indian major carps. These backyard hatcheries generally produce only fry, which are not suited for stock enhancement purposes, unless grown to advanced fingerling stages (Plate 22). Backyard hatcheries are generally effective, not capital intensive and are managed by at most, two persons. In Orissa, India, for example, community-based carp hatcheries are successfully run by village women (Radheyshyam 2001). These community-based hatcheries enable poor women who do not have pond resources to be engaged in fish-related activities, providing them with additional household income. Such hatcheries tend to contribute significantly to rural aquaculture development and indirectly, to poverty alleviation in rural communities.

Fry production is often separated from fry to fingerling rearing, and this ist the bottleneck for most stock enhancement and extensive aquaculture. In the authors’ view, one of the most effective fry to fingerling rearing systems is found in Viet Nam. Here the fry produced in hatcheries are often reared to advanced fry stages in concrete tanks in the hatchery complex itself, and the rearing of advanced fry to fingerlings is carried out in earthen ponds owned by fingerling producers (Plate 23), who may be many hundreds of kilometres away from the former sites. This division of labour offers many advantages - higher rate of survival to fingerling stage, better distribution of income, the spread of aquaculture-related activities into a wider area of the country and easier access to fingerlings for aquaculture and stock enhancement purposes. In addition, it also contributes to income generation in rural areas.

Sen et al. (undated), in one of a few such studies in the region, studied fingerling production systems in three provinces in Viet Nam (Hoa Binh, Thai Nguyen and Yen Bai). These authors recognized four categories of fingerling production/rearing/nursing systems:

• hatchery-based nursing systems;

• full or part-time private pond-based nursing systems near hatcheries or main centers;

• part-time private nurseries in remote areas; and

• part-time cage culture.

These authors observed that the demand for smaller-sized fingerlings (6 cm) occurred around April-May, that for medium-sized fingerlings for cage and paddyfield stocking around May-August and finally, that for the largest fingerlings (12 cm), for stock enhancement in reservoirs, in September-November. Sen et al. (undated) conducted a preliminary economic analysis of the different production/nursing systems (Table 29), and found that there was a large variation in net income among farmers using a particular practice, as well as between practices. These individual variations were attributed to differences in the number of production cycles, survival rates, species cultured, farmer knowledge, pond management practices and time spend on other economic activities.

The use of cages in fry to fingerling rearing is becoming increasingly popular in some countries, particularly those having large numbers of perennial waterbodies (Plate 24), such as Sri Lanka (Ariyaratne 2001, Pushpalatha 2001) and Viet Nam (Bui and Nguyen 2001). Generally, the initial investment and labour costs in cage fry to fingerling nursing are much higher than those for comparable activities on land. However, these costs can be balanced through the relatively high profitability of the former. Ariyaratne (2001) suggested that feed costs in cage nursing can be reduced by harvesting small fish species such as minor cyprinids from the perennial waterbodies where cage-culture operations occur (De Silva and Sirisena 1989). Minor cyprinids are not used for human consumption, but for preparing low-cost, farmmade feeds (Plate 25) of relatively high protein content by sun drying, powdering and mixing with other agricultural by-products.

Unfortunately, fry to fingerling rearing has received only marginal attention from researchers and governments in Asia. In many countries, the processes have evolved and adapted as a result of rural entrepreneurship, rather than through governmental encouragement and backing. The dearth of well planned studies comparing different fry to fingerling rearing systems in Asia is also bound to retard development and adoption of these practices as an alternative livelihood in rural areas, in spite of the scope and the demand for expansion and the products.

Table 29. A summary of the preliminary economic returns from different fingerling production/rearing systems in Viet Nam (based on data from Sen et al. undated)

¹ 1 US$ = 14 500 VND.