1. Introduction

Fishing has always been and for the foreseeable future will remain, a major source of food and income for society. However, its importance relative to other food production systems has evolved, especially over the last half century, as a result of the way fisheries are exploited (FAO 1997). This is especially true of fishery activities in inland waters.

Although the diversification of aquatic resource use through aquaculture is prevalent in most developing countries, in some countries its impacts have been less widely felt than in others, and fishing for food has remained a sustainable activity. It is evident that in many developing countries, capture-based fisheries are also under threat from development, and shifts in fishery management activities to support production from culture-based fisheries and aquaculture are occurring. In this context, capture and culture fisheries must be seen as complementary activities and not as alternatives, as this could potentially lead to reduced production from a particular waterbody (Cowx et al. 2004).

1.1 Contribution of fish to food security and human nutrition

A significant proportion of the world’s people use the living aquatic resources of inland waters for food and recreation. Recent evidence indicates that the number of people dependent on these resources is far greater than previously thought. Studies also show fish to be particularly important in the livelihoods and diets of the poor, providing an inexpensive source of animal protein and essential nutrients not available from other sources.

Fish is an important dietary component in Asia, where its contribution as a percentage of the animal protein intake is the highest in the world (Figure 1), amounting to 23.3 percent as opposed to the world average of 15.9 percent. This situation is to be expected for at least two reasons:

• Fish production, from both capture and culture fisheries and aquaculture, is higher in Asia than in other continents. For example, the most recent data available (that for the year 2000) show that six of the top-ten countries in terms of marine and inland capture fisheries production were Asian, and that these six countries accounted for 34.5 million tonnes (55 percent) of the total landings of the top-ten countries, and 91.3 percent (41 724 469 tonnes) of the global aquaculture production (2002 figures from FAO FISHSTAT 2004); and

• There is cultural affinity for fish in many Asian countries. This dates back to some of the earliest civilizations in the region, possibly as a result of the establishment of major communities alongside major rivers (Asia has a relatively high river index, and the great bulk of the river lengths fall within the tropical region). Wet-rice cultivation was also developed by these early civilizations and, to this day, rice fields have strong association with the harvesting of fisheries products. As these societies developed, their water management and irrigation practices developed to increase rice production and associated fishery benefits. An idea of this can be gained from Plate 1, which depicts a 2000-year-old Sri Lankan inscription indicating the taxation laws in force on inland fish harvests and a stone mural from the Bayon Temple, Siem Reap, Cambodia, depicting fish being consumed at a festival.

Figure 1. Contribution of food fish, as a percentage of total animal protein intake, to human diet: 2000. Redrawn from FAO (2003)

Possibly the best evidence of the continuing importance of fish in the diet in some of the poorer countries in Asia is the amounts consumed in regions/countries such as Siem Reap Province in Cambodia (80-85 kg/caput/yr), Bangladesh (48.3 kg/caput/yr) and Sri Lanka (54.3 kg/caput/yr) (Table 1). Note that in many cases this fish consumption is derived primarily, if not entirely, from inland fishery resources and not from marine capture fisheries, as is the case for Pacific island countries or developed countries with good transport infrastructure.

In most of Asia, and particularly in the Lower Mekong Basin, fish and other aquatic animals are the most important source of animal protein and thus a major support to food security, particularly for rural populations. Apart from fish, frogs, tadpoles, snails, molluscs, shrimps, crabs, snakes and other reptiles and water birds from wetland habitats are considered "aquatic animals". Average basin-wide consumption of fish and other aquatic animals is estimated at 56 kg/capita/yr (Hortle and Bush 2003). In high-yielding fishing areas such as in rural communities of the floodplains around the Great Lake (Tonle Sap) in Cambodia, fish consumption is as high as 71 kg/capita/yr (Ahmed et al. 1998). Even in mountainous regions like Luang Prabang in the Lao PDR, which present physical-geographic conditions similar to those of the central highlands in Viet Nam, northern Thailand or northeastern Cambodia, fish and other aquatic animals account for 55 percent (29 kg/capita/yr) of the total animal protein intake of the human population in rural areas (Sjorslev & Coates 2000). In An Giang Province in the Vietnamese Mekong Delta, consumption of fish, other aquatic animals and their processed products is reported to be as high as 58 kg/capita/yr (Van Zalinge et al. 2004, Hortle et al. 2004).

Table 1. Fish consumption in some of the poorer countries in Asia (data from Van Zalinge et al. 2004)

1 LMB = Lower Mekong Basin.

Although contributing only 2.63 percent to Sri Lanka’s gross national product (GNP), locally produced fish products and imported dried marine fish account for more than 65 percent of the total per capita animal protein consumption (NARA 2000), rising to an estimated 81 percent in rural areas (Nathaniel 2000). Compared to similar rice-growing areas in Southeast Asia, poor families in Sri Lanka are much more reliant on purchasing fish than on harvesting aquatic animals from rice fields and waterbodies themselves. In rural areas, demand is predominantly for locally produced, highly fresh and low-cost tilapias (Murray et al. 2001).

Fish is a food of excellent nutritional value, and it makes a very significant contribution to the diet of many fish-consuming communities in both the developed and developing world. Fish provides high quality protein and a wide variety of vitamins and minerals, including vitamins A and D, phosphorus, magnesium, selenium and iodine. Fish is also a valuable source of essential fatty acids, and its protein is easily digestible. The protein and calorific supply from fish to the global diet has increased marginally over the last two decades, and now contributes about 16 and 7 percent, respectively (Table 2).

Table 2. The contribution of fish to human nutrition (source: Barbara Burlingame, Nutrition Department, FAO, Rome)

Apart from supplying protein and calories to human nutritional well-being, fish is the main source of a number of fatty acids that are often lacking in red meat. These fatty acids, in particular, are eicosapentanoic acid-EPA (20: 5n-3), docosahexaenoic acid-DHA (22: 6n-3) and arachidonic acid-AA (20: 4n-6). The human body is incapable of synthesizing these fatty acids and they must be supplied in the diet. Fatty acids are crucial to life, and apart from being energy sources, some of the long-chain n-3 and n-6 series fatty acids (commonly known as polyunsaturated fatty acids or PUFAs) perform a number of physiological functions, such as:

• providing the structural elements of cell membranes;

• acting as precursors to eicosanoids, a heterogenous group of highly active "local hormones";

• contributing to osmoregulation;

• influencing reproduction and egg quality;

• being important for brain development; and

• being important for development of vision.

It is now well documented that deficiencies of some these PUFAs are associated with major health risks (Stansby 1990, Ulbricht and Southgate 1991, De Deckere et al. 1998), and some diseases and clinical conditions can be alleviated by the supplementation of PUFA (Hunter and Roberts 2000). As a result of this increasing awareness on the importance of fatty acids in the human diet, there is a general upsurge in fish consumption in many societies, particularly in the developed world.

The evolutionary development of the human brain has also been linked to food sources rich in n-3 (DHA) and n-6 (AA) PUFAs, Indeed, there is emerging evidence suggesting that Homo sapiens evolved not in a savana habitat, but in a riparian or coastal habitat that was rich in fish and shellfish resources (Crawford et al. 1999). There is increasing evidence from medical studies indicating the positive effect of fish in the diet on human health, growth and general well being. No attempt will be made to review this in detail, but suffice it to say that man’s current nutritional requirements reflect an early dependence on fish and other aquatic animals in the diet.

1.2 Sourcing foodfish requirements

The Asia-Pacific region is the world’s largest producer of fish, from both aquaculture and capture fishery sectors. In 2002, this amounted to 46.9 million tonnes from aquaculture and 44.7 million tonnes from capture fisheries. The total inland fisheries production of the region in 2002 was reported as 3.4 million tonnes. South Asia and Southeast Asia contributed the greatest production as compared with other subregions (Sugiyama et al. 2004).

It is generally recognized that marine capture fisheries, which witnessed a period of major growth following the Second World War, have now reached the point where they are no longer increasing and indeed, several are in decline. This is not surprising given the status of the major stocks of marine fish and the fact that nearly 45 percent of these stocks are already fully exploited (Figure 2).

Global marine capture fisheries are influenced by climatic events, such as El Niño and La Niña, which are known to affect the world’s biggest single-species fishery (the Peruvian anchovy fishery) once every few years. Apart from heavy fishing effort in marine capture fisheries, ecosystem degradation is also an important factor contributing to declining fisheries production (Jackson et al. 2001, Myers and Worm 2003).

It is within the above context that a concerted attempt has been made since the 1960s to develop aquaculture by transforming it from an art to a science. Globally, this attempt has been successful, when one considers that the total aquaculture production in year 2000 was 45.7 million tonnes and that aquaculture has grown at an annual rate of 8.9 percent/yr since 1970 (Tacon 2003). Currently, aquaculture accounts for 33 percent of every kilogram of aquatic products consumed in the world. Although aquaculture has been the fastest growing food production sector, the question arises whether this pace of growth can be sustained and for how long. It has been shown (De Silva 2001) that the rate of production is declining in all continents except South America. A number of reasons for this trend have been recognized, including the fact that land-based aquaculture must increasingly compete for land, water and feed resources with other agricultural sectors and that parts of the sector are reliant on marine fishery-based resources (e.g. fishmeals). These factors influence the economic feasibility and competitiveness of aquaculture with respect to the other animal protein production sectors.

Figure 2. A schematic representation of the status of the exploited fish stocks in relation to fishing mortality and biomass (re-drawn from Botsford et al. 1997)

Inland fisheries are increasingly being re-evaluated as an economically efficient and equitable way to contribute to foodfish supplies, particularly in developing countries (Welcomme and Bartley 1998, De Silva 2000, Lorenzen et al. 2001).

Production from inland fisheries is currently reported to account for about 10 percent of global fish supply (Figure 3). While this contribution may seem to be relatively low in comparison to marine capture fisheries, there is a general consensus that inland fisheries production in many regions is grossly under-estimated. A recent estimate of the potential range of production for some Southeast Asian countries suggests that these under-estimations are in the order of 2.5 to 3.6 times greater than those reported (Coates 2002). This suggests that the contribution of inland fish to the world’s fish supplies is significantly higher than the estimated 10 percent and consequently, that the role of fish in the nutrition of the rural poor is also greatly undervalued.

Figure 3. Total global and inland fisheries (capture & aquaculture) production and the percentage contribution if global inland capture fishery production

Figure 4. Total Asian fishery production and total Asian inland fishery production (aquaculture and capture fisheries) and the relative percentage contribution of inland capture fisheries (source: FAO FISHSTAT 2004)

The fact that inland fisheries production is underestimated does not mean that the fisheries are in good condition. There are consistent published and anecdotal reports that most riverine fisheries in the region are in decline. For example, since 2000 fishing bans have been imposed in different sections of the Yangtze River, PR China during certain times of the year to make provision for the different spawning periods of the major fish species (Anon 2003). In Bangladesh, riverine fish production declined from 207 000 tonnes in 1983 to 124 000 tonnes in 1998, and during this period the landings of indigenous major carps decreased by 77 percent (De Graaf 2003).

Although inland fish production is undoubtedly important in Asia, its increasing contribution to the fish supplies is masked by the substantial increases in aquaculture production, particularly in PR China (Figure 4). Increasing production from inland fisheries is not confined to Asia. There has also been a relatively recent upsurge in inland fish production in the tropical countries of South America, particularly from reservoirs (Petrere 1996, Quiros 1998). This apparent increase in production also reflects an improved assessment of the real participation of rural people in inland fisheries and their consumption of inland fishery products (Hortle et al. 2004, Almeida et al. 2004)

Apart from their contribution to the total fish production per se, inland fisheries and aquaculture are important to food security in many other ways. Notably, inland fisheries production:

• directly supplies inland rural populations with an affordable source of high quality animal protein;

• is almost entirely used for direct human consumption (Plate 2);

• is rarely converted into feed ingredients for farmed animals, including those used in aquaculture (unlike marine fish production), of which nearly 25 percent is converted into fishmeal.

• enables persons with minimal skills to be engaged in resource exploitation at a subsistence level (although global figures for inland fishers are rather low, they typically under-estimate the seasonal or occasional nature of inland fishing and therefore, grossly under-estimate actual participation and dependence upon inland fisheries).

Inland fisheries provide direct employment to rural populations through production and indirect employment through processing and trading in fishery products. Importantly, inland fisheries also provide significant opportunities for integration into rural farming livelihoods, help to buffer against shortfalls in agricultural production and provide alternative sources of food and income. Most inland fisheries require very little entry capital and are often practiced as part-time activities. Examples include the operation a few traps in a paddy field or a channel (Plate 3) and children foraging for shellfish and other aquatic animals in paddy fields and wetland areas. Such exploitation is often conducted as part of the farming system and is often environmentally non-destructive.

1.3 Purpose of this review

As inland fisheries decline through habitat changes that accompany agricultural and land developments and intensifying exploitation, it becomes increasingly important to consider ways and means to sustain the availability of fish to rural populations. One of the main strategies that has been employed in most Asian countries to improve inland fish production is the stock enhancement of inland waters, particularly lacustrine waterbodies. Although stocking has been practiced in many countries in the region, its cost-effectiveness and impacts on rural communities have been rarely evaluated. This document will review and evaluate the following aspects of inland fishery enhancement:

• the diversity of enhancement practices that are employed in the region;

• the impact of these practices in relation to the type of waterbody and management structures in operation;

• the cost-effectiveness of enhancement practices in relation to the nature of the waterbodies;

• the organizational structures/institutions that are needed to sustain the practices;

• the biological and ecological impacts of current enhancement practices, including their effects on biodiversity; and

• the impacts of enhancement practices on rural livelihoods.

Specific examples of inland fisheries enhancement are drawn from Bangladesh, India, Indonesia, Myanmar, Sri Lanka, Thailand and Viet Nam. In view of the diversity of inland waters, this review will also consider the water resources in Asia and the suitability of different types of waterbody for adoption of enhancement and management strategies to enhance fish production.