1Fish Pathology Laboratory, Department of Aquaculture
College of Fisheries
Mangalore-575002, India
2Department of Fisheries Economics
College of Fisheries
Mangalore-575002, India
Mohan, C.V., and R. Bhatta. 2002. Social and economic impacts of aquatic animal
health problems on aquaculture in India. p. 63-75. 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.
Assessing the socio-economic impact of disease on rural aquaculture is vital in order to implement primary health care. However, because of the complexities surrounding such an assessment, it is not an easy task. Rural aquaculture includes culture-based capture fisheries, trapping systems, traditional fish farming in family ponds and modified extensive or semi-intensive culture systems. The impact of disease may differ in each of these systems. To understand the impact, it is vital to understand how the different culture systems work and how fish health influences the performance and yield in these systems. Mechanisms for assessing the impacts of disease in different culture systems should be based on well thought-out protocols. More often, the concept of socio-economic impact assessment is lost when assessments are carried out for only those epizootic diseases that result in total mortality and crop loss.
This paper examines health problems in aquaculture, constraints to implementation of adequate health management in different aquaculture systems, and protocols for quantification and assessment of health-related losses, and attempts to define health management costs. The socio-economic impact of epizootic ulcerative syndrome (EUS) and white-spot disease on rural aquaculture is examined in detail using primary and secondary information. Four case studies from different rural aquaculture systems look into the socio-economic impact of disease.
Twenty years ago, aquaculture in India was a subsistence activity. Now, in many parts of the country, it has also transformed itself into a commercial activity. Realising the contribution of aquaculture to the national economy, rural employment, poverty alleviation and food security, several policy changes have been brought about at the macro-economic level, giving a new impetus to freshwater aquaculture.
India has vast resources with potential for aquaculture. Aquaculture production in India was 1.77 million mt in 1996, with 1.68 million mt coming from freshwater fish and the rest (O.09 million mt) from shellfish. Carps are widely cultured, and in 1996, they contributed some 1.56 million mt i.e., 88.5% of the total aquaculture production of the country (Ayyappan 2000). Freshwater aquaculture depends mainly on carp-culture practices that have proved sustainable at different levels of production over the years. Production comes from over 2.25 million ha of ponds and tanks, 1.3 million ha of oxbow lakes, 3 million ha of reservoirs and 1.2 million ha of coastal brackishwater area.
The expansion and intensification of aquaculture is bound to bring problems, and disease may be very significant. Epizootic ulcerative syndrome (EUS) of fish and white-spot disease of cultured shrimp have amply demonstrated the socio-economic impacts of aquatic animal disease on rural aquaculture. Economic losses due to disease are likely to increase as aquaculture expands and intensifies. Systematic assessments of the social and economic impacts of disease on rural aquaculture are needed, as they may bring to light the need for adoption of farmer-oriented, environmentally friendly, integrated primary health management packages for rural aquaculture. Impact assessments focused on small-scale rural aquaculture are lacking, and consequently, there is lack of prevention, diagnosis and treatment of diseases in rural aquaculture. As a consequence, significant losses are impacting on small-scale, rural aquaculture development in India.
Different aquaculture systems will experience different types of health problems, the majority of which will produce chronic mortalities. Unlike the acute losses associated with disease epizootics, chronic mortalities often go unnoticed. Acute losses attract the attention of fishers, fish farmers, socio-economic analysts, planners and administrators, and it is usually only these losses that are analysed for their impact on rural aquaculture. The socio-economic impact associated with chronic losses may be many times higher than that resulting from the routinely assessed acute losses. As a first step, it is necessary to understand which pathogens and what types of disease can cause significant socio-economic impacts in culture-based capture fisheries and culture fisheries and affect the livelihoods of fishers and farmers dependent on rural aquaculture.
There are several aquatic animal health problems in culture-based capture fisheries that influence production from such systems. The disease that has made the greatest impact is EUS. Since 1988/89, EUS has caused significant production losses in many of the culture-based capture fisheries in reservoirs, lakes, beels (floodplain lakes cut off from river meanders), brackish waters and irrigation tanks (Mohan and Shankar 1994). A detailed analysis of the impact of EUS is presented later in this paper. Several bacterial, parasitic and fungal diseases have been documented in open-water systems practising culture-based capture fisheries. Ulcerative bacterial diseases, myxozoans, monogeans, digeneans, larval cestodes and ectoparasitic crustaceans have been regularly reported. Reports of mortalities associated with these pathogens are few; however an absence of recognisable acute mortalities does not mean that these pathogens do not have an impact. Some of these pathogens are certainly responsible for significant chronic mortalities and poor growth that will be reflected in low survival and poor yield. Some of the larval digeneans and cestodes present in the body cavity and muscle of large fish can affect marketability.
Another serious problem observed in some of these systems is acute mass mortalities associated with domestic sewage and industrial effluent discharge. Every year several cases occur; however, unless strict regulatory measures are in place, little can be done. Sudden unseasonal rains bringing large quantities of silt or pesticides from the catchment areas into these water bodies can cause sudden mass mortalities. Fish health problems in culture-based capture fisheries may thus have serious socio-economic impacts. Little can be done in terms of management, in this multiple-user common resource. However, there are some areas where interventions can be attempted. These include the stocking of advanced fingerlings instead of spawn, fry or early fingerlings; stocking of resistant varieties; development of stocking policies and science-based fishing regulations to encourage the development of sustainable multi-species fisheries; and application of measures to avoid using these water bodies for sewage and industrial effluent discharge.
Aquatic animal health problems in pond culture and their impacts on yield are well known, but are not often quantified due to the difficulties in collecting accurate and reliable quantitative information. Traditional rural carp culture in ponds was an ancient practice in the states of West Bengal, Orissa, Assam and Tripura. Now, scientific culture of Indian major carps has become a common practice in many parts of Andhra Pradesh, Punjab, Haryana, Orissa, West Bengal and Karnataka, where aquaculture is becoming the main occupation. Traditional pond culture as a secondary occupation to agriculture is also very common in various parts of India.
Diseases of varied aetiology are a serious constraint to the success of many of these culture systems. EUS has had a significant impact on pond-cultured fish in many parts of northern India. Primary and secondary bacterial infections, opportunistic fungi, ectoparasites (e.g., protozoans, monogeans, fish lice and anchor worm) and endoparasites (e.g., myxosporeans) are some of the pathogens that have had a significant impact on the yield and performance of these pond-culture systems. Many of these pathogens are also important in carp hatcheries and seed production centres. It is increasingly recognised that disease syndromes with mixed aetiology play a more important role than previously thought. In the carp-culture systems of Andhra Pradesh, much of the chronic mortality can be attributed to primary damage caused by ectoparasites and secondary infection by bacteria and fungi.
Compared to carp culture, the impact of diseases on shrimp culture has been more significant. Prior to July 1994, Indian shrimp farms did not experience serious disease problems. Conditions such as external fouling, shell and appendage necrosis, luminescent vibriosis, systemic and enteric vibriosis, soft-shelling and monodon baculovirus (MBV) were regularly reported from farms along the east and west coasts. These diseases were responsible for low levels of mortality in several farms, but not for mass mortalities over large areas. Since July 1994, diseases of viral aetiology, notably, white-spot disease, have had a disastrous impact on the shrimp farming activity of the country.
Assessing the impacts of disease, even in aquaculture systems, is not easy, as only acute losses are recognised and quantified. Chronic mortalities and poor growth caused by disease are not recognised; hence, there is a strong need to use indicators to assess these chronic losses.
Compared to culture-based capture fisheries, health management in pond aquaculture should be feasible and easy to implement. The major problem, however, is the lack of an holistic health management approach, health management often being equated with chemotherapy. It is essential that fish farmers be made aware that simple husbandry practices could significantly reduce disease-related losses. These include pond drying, liming, selecting good seed, using proper size at stocking, applying prophylactic treatment of seed at stocking, and assuring periodic sampling, good pond productivity, good feed, and regular monitoring of fish health and water quality. Farmers should become well versed in farm-level diagnostics and health management. Surprisingly, only a small percentage of farmers are able to diagnose health problems and rectify them. The vast majority simply resort to the indiscriminate use of antibacterials and pesticides at the first sign of mortality (Rao et al. 1992). Lack of diagnostic capability, coupled with misuse of chemicals, can have serious repercussions. Many health problems originate in the seed-rearing farms but manifest themselves clinically, producing mortality, under farm conditions (Mohan and Shankar 1995, Mohan et al. 1999a). In such cases, farmers, in spite of applying adequate primary health care, can lose their entire crop. To ensure sound farming with minimal disease losses, primary health management should start with seed production.
Quantifying losses caused by disease should be the first step towards assessing the socio-economic impact of disease on rural aquaculture and culture-based capture fisheries. In order to quantify disease losses, fishers and farmers should be able to identify disease as the reason for crop loss, slow growth or poor harvest. The primary task should be to train farmers to carry out field-level diagnosis and assess the likely impact of disease. Several indicators may be used to quantify health-related losses in aquaculture and capture-based fisheries. Differences between expected yield and actual yield, percentage survival and growth rate may give some indication regarding health related-chronic losses in aquaculture systems. Such estimates will be crude, since many other factors can contribute to poor survival, poor growth and production loss.
Assessing losses in culture-based capture fisheries is also difficult. Species composition in commercial landings, species-wise size distribution, annual landings and catch per unit effort (CPU). may give some indirect indication of disease losses. For example, in some fresh- and brackishwater systems catches of snakehead (Channa spp.) and pearlspot (Etroplus), respectively, have declined considerably. This could be a direct consequence of EUS in natural water bodies.
The indirect effects of aquatic animal disease may also have negative socio-economic impacts. The zoonotic potential of some fish pathogens, bacterial drug resistance in human pathogens, and tissue residues of chemotherapeutants are all-important. Health management strategies should aim to minimise the indirect socio-economic consequences of aquatic animal disease.
Identifying health management strategies and defining health management costs to reduce or prevent disease losses are very important. Under the broad definition of rural aquaculture, it is necessary to see where, and in which culture systems, health management strategies can be employed. It should be possible to introduce health management strategies in all farmer-controlled aquaculture ponds and tanks. In culture-based capture fisheries, as in reservoirs and large irrigation tanks, it may not be possible to introduce any standard health management package. However, under species enhancement programmes, stocking of selective disease-resistant species and larger-sized fish could be explored.
It is difficult to define what should be included under health management costs. Often, only the cost of chemotherapeutants used during or prior to disease outbreaks is included under health management costs, a gross underestimation in any aquaculture system. Health management costs will vary in relation to the farming system and species cultured. Aspects of management that have a bearing on the health of the animals cultured should be considered. Broadly speaking, health management costs would include a proportion of the cost that is incurred towards the following: farm siting and layout, water source, seed screening systems, pond reparation, feed quality, pond management, prophylaxis and chemotherapy.
EUS, since its first appearance in India in 1988 in the northeastern states, has spread to the rest of the country, and still occurs in wild fishes during winter months in fresh water and during monsoon in brackishwater systems. EUS had a very strong socio-economic impact within the first few years of its appearance. The most severe impact has been on small-scale, mixed-species, capture fisheries from rivers, reservoirs, oxbow lakes, irrigation tanks, estuaries and backwaters. This impact was primarily felt by the fishers who depended on capture fisheries as their only source of livelihood. The disease caused large-scale mortalities and loss of valuable edible fish. In addition, most of the wild fish caught were affected and could not be marketed because of the unsightly ulcers on the body surface. At the same time, other unaffected, healthy fish species, caught from affected waters during the EUS season, could not be marketed, as people were afraid to buy fish. The public scare this disease created compelled many district and state administrative authorities to impose a temporary ban on capture fisheries in many water bodies and on the sale of fish brought from such sources. Consequently, poor fishers throughout India faced extreme hardship during the initial years of EUS.
Several estimates were made of the socio-economic impact of EUS during its initial two to three years of occurrence. The economic loss in Bihar during 1990 was estimated at US$150,000; in Orissa during 1989-91, it was estimated at US$95,000; and in Kerala during 1991-92, at US$625,000 (Das 1994). However, earlier estimates considered almost every freshwater fish as susceptible and affected.
Several issues surrounding EUS are now better understood, and the negative socio-economic impacts experienced earlier are now no longer seen. There is a growing opinion that EUS is not as severe as it was, and it is now taken for granted. There is a degree of complacency, and this may cause some problems. The socio-economic impact also seems to have reduced; however, this widely held belief should be viewed with some caution. Closer examination of the relationship between EUS and the population density and structure of susceptible fish populations in natural waters is needed. Even now, during the EUS season, small numbers of affected fish are caught from natural waters. The number of affected fish caught from a natural water body should not be used to assess the biological impact of the disease and the virulence of the pathogen. Little information is available on the species composition and landings of susceptible populations for the years before and after the highest prevalence of EUS. It is becoming increasingly clear that populations of highly susceptible species like Channa, Puntius, and Etroplus are dwindling in many of the natural water bodies. As a result, smaller numbers of susceptible species are seen to die during the EUS outbreak season, giving the impression that the disease is not severe. The disease certainly has had a major impact on the population density and structure of susceptible species, and hence, on aquatic biodiversity, although this has not been examined in detail. Fishes like Channa and Etroplus -fetch a very good market price in many parts of India, and the dwindling catches of these species are affecting the fishing population, who are dependant on fresh- and estuarine capture fisheries for their livelihoods. An integrated study is needed to look into the impact of EUS on species diversity and the population structure and density of susceptible fish species in natural waters. The biological and socio-economic impacts could be very significant.
Available data on the impact of EUS on carp culture in ponds are highly varied and inconsistent, and it is, therefore, difficult to draw conclusions about the socio-economic impact. Bhaumik et al. (1991) reported that 73% of the culture ponds in West Bengal were affected, most ponds having lost 30-40% of their stock. On the contrary, although EUS appeared in the natural waters of Andhra Pradesh, reports of the disease in the well-developed, semi-intensive aquaculture ponds are unknown. Earlier reports from India considered all ulcerative skin conditions in major carps as EUS, and this has led to confusing impact assessments and generalisations. This was partly because there was, at that time, no case definition for EUS and much less was known about the disease. Now, much new information has emerged on the susceptibility of different freshwater fishes to EUS. Several studies suggest that Indian major carps are either less susceptible or refractory to infection (Mohan and Shankar 1994). Of the three Indian major carps, mrigal is considered more susceptible than catla and rohu. Histopathological studies of natural outbreaks have clearly shown that Indian major carps are able to mount a better inflammatory response and resist the fungal invasion better than the more susceptible Channa and Puntius. Experimental infections have also shown that the typical clinical and pathological features of EUS can be induced in snakehead in seven to ten days following co-habitation or injection, while it is not possible to reproduce the disease in the same time period in major carps (Mohan et al. 1999b). In light of this latest information, retrospective analysis of Indian major carp culture in Andhra Pradesh during earlier EUS outbreaks suggests that EUS was not that significant in producing crop losses in culture ponds. Several surveys carried out since the occurrence of EUS in the carp-farming belt of Andhra Pradesh have identified only parasitic and bacterial diseases as major causes of crop loss.
In view of their relative resistance to EUS, the following strategies are suggested for managing EUS in cultured Indian major carps:
Culture-based fisheries are capture fisheries that are mostly or entirely maintained by the regular stocking of seed. These culture-based fisheries rely entirely on the natural productivity of the water body for growth and on artificial stocking for recruitment. Such fisheries exist in several lakes and reservoirs in India, with Indian major carps and common carp increasingly being stocked. In many of the reservoirs, this practice is well established, resulting in positive socio-economic benefits to fishers.
During the initial two to three years of its occurrence in India, EUS had a significant socio-economic impact on culture-based capture fisheries. Massive mortalities decreased the production from many water bodies, a large proportion of the fish landed were affected, and even healthy fish caught from such water bodies could not be marketed. As a result, private and government species enhancement programmes were abandoned. However, culture-based capture fisheries have since recovered and are now the mainstay of many fishers and fish farmers. Selective decimation by EUS of susceptible species like snakehead may have had a positive impact on carp fisheries in some of these culture-based capture fisheries, however, this needs to be examined in greater detail.
Traditional shrimp trapping systems have been used in the low-lying brackishwater areas of Kerala, Karnataka and West Bengal for several years and are largely seasonal in nature. Auto-stocking, aided by tides, is practised, and production is very low, averaging 100-500 kg/ha/crop. India has vast potential for the development of commercial shrimp farming, having 1.2 million ha of coastal brackishwater area. Realising the enormous potential, the government identified aquaculture as a "thrust area" to augment exports and earn much-needed foreign exchange. Between 1988 and 1994, the shrimp farming industry experienced phenomenal growth. The booming industry encouraged the development of several hatcheries, feed mills, and other aqua-related ancillary industries. The total area presently in use is estimated to be 120,000 ha, of which around 50,000 ha is still under traditional systems producing, in total, about 95,000 mt of cultured shrimp.
In less than ten years, serious viral diseases and environmental issues have threatened the industry. The direct and indirect socio-economic impacts of diseases in shrimp farming are difficult to quantify. The economic loss in 1994 alone was put at US$17.6 million (Alagarswami 1995, Venkatesan 1996). The indirect effects were felt by the hatcheries, feed companies, aquaculture chemical companies and other ancillary industries. The collapse of the industry has caused job losses at both the technical and non-technical levels. As more than 80% of the farms are owned by small operators, there has been a significant socio-economic impact on small-scale farmers in coastal regions. Continuous crop failures, high lease values and erosion of profits have forced some operators to abandon their shrimp farms. These abandoned shrimp farms present a major challenge to both coastal resource managers and pond owners, because of their limited land-use prospects.
Information from four case studies from different types of rural aquaculture systems, including commercial carp farming, is presented in order to understand the socio-economic impacts of aquatic animal disease on rural aquaculture.
Carp farming in Andhra Pradesh has redefined the concept of carp farming in India. The three to six species used in traditional polyculture systems have been replaced by only two species. This practice has become well established in large areas of Andhra Pradesh, and successful farming has now been going on for more than 15 years. Carp farming in Andhra Pradesh is now regarded as sustainable and is contributing, both directly and indirectly, to the livelihoods of several thousand people. Examining aquatic animal health problems in these scientific carp farming systems provides some insight into the likely socio-economic impacts of fish disease on commercial rural aquaculture.
In an International Development Research Centre (IDRC)-sponsored survey of carp farming practice, information was collected from 189 farms from four districts of Andhra Pradesh during 1991-93 (Veerina et al. 1993). About 50,000 ha is under scientific carp farming in the Kolleru Basin. The average farm size is 10.5 ha [0.3-81 ha), while that of a culture pond is 3.9 ha (0.3-20 ha) and that of a rearing pond is 0.6 ha (0.04-3.O ha). Nearly 75% of the farmers follow a two-species system comprising catla (23%) and rohu (77%). Bottom dwelling mrigal have been eliminated because of the difficulty in harvesting and the low market demand. Total elimination of mrigal from culture systems may also have hidden advantages in terms of preventing EUS outbreaks in culture ponds. The mean stocking density is around 2,900 stunted yearlings per hectare. The ponds are heavily fertilised with organic (19,000 kg/ha/yr) and inorganic (2,323 kg/ha/yr) manures. De-oiled rice bran and groundnut oil cake are fed at about 27,000 kg/ha/yr. Salt is regularly used as a feed additive. Liming is routine and CaO is used at the rate of 940 kg/ha/yr. The average culture period is 10 months, but varies from 6-15 months, as farmers practice phased harvesting. The average size at harvest is 1.8 kg for rohu and 2.7 kg for catla. The average gross yield for this two-species system is 5,890 kg/ha/yr, the best production being 7,900 kg/ha/yr. The return on investment (ROI) is 1.65. A major proportion (76%) of the farmers were rice cultivators before their entry into aquaculture.
Diseases are one of the major constraints, and most farmers are aware of the consequences of disease on growth, survival and final production. A small percentage of farmers are able to identify disease problems and quantify disease-related losses, while the majority are dependent on friends, consultants, salespersons or pharmacists for advice on diagnosis and medication. This well-planned and executed study has identified the major health problems in carp farming but was not able to quantify either health-related losses or the health management costs incurred by farmers.
In another study carried out to prepare a country-status paper in 1990 on the use of chemotherapeutants in fish culture in India, information was collected from 200 farm ponds in Andhra Pradesh. Details of the disease problems, chemicals used, treatment methods followed, problems and constraints are highlighted in Rao et al. (1992). The present situation remains much the same concerning occurrence of disease, farm-level diagnostics, and use of antibacterials and pesticides. Ectoparasitic diseases account for 70% of the problems, while bacterial and fungal diseases account for 27.5% and 2.5%, respectively. Losses of 40 million Rupees (Rs) (US$1 million) due to disease-induced mortality and impaired growth are incurred annually in Andhra Pradesh.
Chemotherapy, based mainly on trial and error, has been developed using locally available antibacterials, pesticides and other common chemicals. On average, farmers spend 10% of production costs on disease treatment. Farmers have become completely dependent on chemotherapy; resorting to treatment at the first sign of mortality or reduced feeding. Easy access to antibacterials and pesticides has increased their misuse.
A wide range antibiotics, sulpha drugs and nitrofurans are used in feed to treat presumptive bacterial diseases. Organophosphorus pesticides like nuvan, malathion and cythion are routinely used to treat for ectoparasites such as Argulus and Dactylogyrus. However, the efficacy of these treatments has never been evaluated. Multifactorial diseases, characterised by primary ectoparasitic infections followed by secondary bacterial infections, have further complicated the success of chemotherapy. Lack of diagnostic skills, coupled with easy availability of chemotherapeutants, has led to indiscriminate use of these chemicals in farmed food fish. Problems of drug resistance in pathogenic bacteria and tissue residues of pesticides have already attracted the attention of planners and the general public.
Immersion treatments with pesticides are routinely followed for ectoparasitic problems. The current application method involves dissolving the required quantity of the pesticide in 10-20 L of water and spraying the solution over the pond surface with a hand-held agricultural sprayer. In large fish-ponds, the sprayers are operated from motor boats. This method is very popular with farmers using nuvan, malathion and cythion to combat Argulus infection. Systemic antibacterial therapy is normally given through feed. The feeding bag method followed in Andhra Pradesh appears to be effective. Normally, for each hectare of pond, 10-20 bags of 50-75 cm size with two rows of perforations at the bottom are tied individually to bamboo poles fixed at regular intervals in the pond. Up to 12 kg of normal or medicated feed can be kept in each bag. Within two hours, most of the feed will be utilised by the fish, a method resulting in minimal feed wastage and antibacterial leaching. The dose used to treat systemic and surface bacterial disease is more or less standardised at around 7-10 gm active concentration/100 kg fish/day for 7-10 days.
These two studies show clearly that disease has a serious impact on rural aquaculture in Andhra Pradesh. It is also clear that health problems are evident only when the intensity of farming operations increases. At the same time, some of the novel changes that have taken place in Andhra Pradesh carp farming have had a positive impact on health management. These include reduction in stocking densities; reduction in the number of species; stocking of large-sized stunted yearlings, use of feeding bags, use of salt in feed, and prophylactic immersion in salt or potassium permanganate solution before stocking.
The first development, unique to Andhra Pradesh and now slowly becoming popular in other parts of India, is the stocking of "stunted yearlings." In this technique, fry procured during the breeding season are held at very high densities (50,000-100,000/ha), fed at 1-2% body weight, and grown for 6-12 months. The farmers assume that the weak and sick fry will die and the healthy ones will become stunted. At the end of one year, the surviving fish attain a size of 100-200 gm. These stunted yearlings are stocked in grow-out ponds at the rate of 3,000/ha. They are normally given a prophylactic bath with potassium permanganate or salt before stocking. Survival rates of 85-95% are very common in these systems, and the average production is 5,360 kg/ha/yr. These stunted yearlings grow to 1.5-2.5 kg in 8-12 months. This practice has completely replaced the earlier system of stocking fingerlings, and there is a considerable improvement in health, survival and production
The second development is the unique "bag feeding technique," previously described. This method allows the farmers to monitor feed consumption, which is a good indicator of health. At the first indication of a drop in consumption, farmers cut down feed and apply chemotherapy. The use of medicated feed in this bag feeding technique is more effective, and the leaching of antibacterials is less.
The development of carp culture in the Riachur area has an interesting background. Large tracts of agricultural land are dependent on Thungabhadra Canal for irrigation. Water is released from the reservoir from July onwards of every year, however, only agricultural lands near the head of the canal get the water without any problem. Land in at the middle and tail end of the canal get water only during July to September and do not get sufficient water at regular intervals to meet their agricultural needs. This has led many farmers at the tail end of the canal to convert a significant portion of their agricultural land to water-storage tanks. These tanks are filled by pumping water from the canal and storing it for year-round agricultural use. These storage tanks are constructed by excavating 2-2.5 m from the original paddy fields and raising the bunds from their original level by another 2.5-3.5 m. The tanks have water depths ranging from 4.5-7 m. A subsidy from the government, at the rate of Rs 10,000/acre (US$217/acre) of constructed pond area, has also encouraged many farmers to convert part of their land to water storage tanks.
These water storage tanks are increasingly being used for farming of catla and rohu. Their culture involves stocking fingerlings in August and September, when the water depth is at its highest (4.5-7 m), and feeding with de-oiled rice bran using the bag feeding technique. Water from the tanks is regularly let out to meet the agricultural needs of the farmer, and by June-July of the subsequent year, the water level will have dropped to 1.25-1.5 m and the fish will have completed 10-11 months of growth. The water is then pumped out, and the fish harvested. Water storage for the next season starts immediately, with little or no time for drying the tanks. The income generated from farming fish in these water storage tanks forms a major portion of the total income of the farmer. This system has been going on for the last three to five years, and more such systems are coming into operation every year. The success of this type of fish culture is encouraging farmers in this region to convert agricultural land to aquaculture operations.
There are about 300 fish farmers in this region, with about 500 ha of water area being used for culture. This case study collected information from 32 farms from eight areas. The farming practices, stocking densities, size at stocking, species stocked, feeding practices, harvest methods and production figures appear to be very consistent. Farmers spend, on average, 10-15% of their time on aquaculture operations. Pond-size ranges from 0.8 to 2.8 ha. On average, 16% (8-30%) of the total land area has been converted to water storage tanks. The experience of farmers in aquaculture ranges from two to four years. Catla, rohu and common carp fry of 5-7 cm length are stocked at an average of 5,000-6,250/ha. Manure is applied at a rate of 1,000-2,000 kg/ha/yr. On average, farmers harvest 4,650 kg/ha of 1.2-1.8 kg fish after a growing period of one year. The income generated from this secondary occupation is substantial (20-40% of the total income). This needs-based practice appears to be sustainable and contributes significantly to the overall income of the farmer. In addition, the farmer is also safe from the uncertainties of water supply for agriculture. A major portion of the agricultural land (70-80%) is used for cultivation of rice and cotton.
This example of small-scale, rural aquaculture development has taken place primarily because of the government-subsidised aquaculture popularisation programme. Information collected from 35 farmers is summarised below. All the farmers are primarily agriculturists cultivating rice, coconut and banana. The total land holdings of individual farmers ranges from 2-4 ha. Under the government scheme, for every acre of pond area, a subsidy of Rs 10,000 is given (US$217). Almost all the farmers surveyed had excavated 0.3-0.4 ha ponds in their agricultural land. Water for the ponds is taken from wells or irrigation canals, and the ponds are stocked with about 4,000 catla, rohu, mrigal and common carp fry of 2.5-3.0 cm in length. The ponds are manured with 2,000-3,000 kg of farmyard manure during the culture period, and about 500-800 kg of rice bran is used for feeding for the entire culture period. A small percentage of the farmers add 125-250 kg/ha lime to the pond. Production from these 0.4 ha ponds ranges from 1,850-2,500 kg, and the monetary gain is substantial. For a single farmer, the income generated from fish (1,950 kg; Rs 58,500 (US$1,272)) is much more than that generated from rice production (4,500 kg; Rs 45,000 ($US978)) from one hectare of land or from coconut production (10,000 nuts; Rs 40,000 [$US870)) from one hectare. The financial benefit that can be gained from growing carp in small ponds in rural areas is making this form of aquaculture a popular activity that is attracting an increasing number of agricultural farmers .
In both the Raichur and Mysore case studies (Case Studies 2 and 3), none of the farmers surveyed experienced total crop losses. The majority of the farmers were unaware of fish health problems and the likely impact they can have on fish growth, survival and yield. Some of the reasons suggested by farmers for poor yield are low fertilisation, irregular feeding, low stocking density and poaching. No farmers suggested the possibility that disease might be a reason for low yields. At the same time, farmers observed low-level mortalities during the colder months of the year and believed that low temperature was killing fish.
Karnataka has 4,000 ha of brackishwater area, of which about 2500 ha is gazani lands (original and reclaimed estuarine and river-basin lands are called gazani or khar lands). Through collective farming, small groups of farmers were using these lands for growing salt-resistant rice during the rainy season and for natural shrimp trapping during the dry season. Shrimp trapping during the dry season was considered an economic boon for small subsistence farmers. This traditional resource management was able to convert a common property into a productive, more sustainable community resource. However, this changed dramatically with the advent of commercial shrimp farming. Lured by higher returns, gazani farmers leased their lands to commercial shrimp farms. This led to large-scale conversion of gazani lands to shrimp ponds. Of the 2,500 ha of gazani land, only 700 ha is still under traditional farming practice, the rest having been converted to shrimp ponds. Initially, gazani farmers were getting higher monetary benefits through receipt of rents; however, all this changed with the occurrence of white-spot disease. Since 1995, large tracts of former gazani lands are lying as abandoned shrimp ponds. The failure of shrimp farming meant loss of lease revenue to the gazani landowners. During 1994-95 and 1995-96, about 1,000 ha of shrimp ponds were affected by the disease, with an annual input loss of Rs 10 million (US$0.23 million) and an output loss of Rs 25 million (US$0.58 million).
The major problem now is the irreversible land development that has taken place. Once excavated and converted, gazani lands are not easily restored to their original natural state or function. The breakdown of traditional methods of community resource management and the subsequent loss of income to gazani farmers is a direct impact of white-spot disease. The direct and indirect socio-economic impacts of white-spot disease on traditional gazani farmers are very evident, but they need to be properly quantified before alternative resource-use programmes for improving the livelihoods of the hundreds of gazani farmers can be developed. The use of abandoned shrimp ponds for fish culture and mangrove plantation are some of the ways by which productive, traditional resources can be put back to use.
The impact of disease on rural aquaculture and fisheries cannot be underestimated. EUS in wild fish and white-spot disease in cultured shrimp have amply demonstrated the potential for aquatic animal diseases to cause significant negative socio-economic impacts on the rural fishers and small producers who dominate much of the aquaculture in India. Continued expansion of carp production for an increasing population is a reality. Economic losses are likely to increase as aquaculture expands and intensifies, impacting on large-scale commercial operators and small-scale farmers alike. The impact of disease on production becomes more evident as small-scale operations transform into commercial operations. In traditional rural aquaculture, there is a serious under-reporting of diseases and a consequent lack of prevention, diagnosis and treatment. As can be seen from the case studies, this is due to a lack of awareness and monitoring, and indicates that avoidable losses are occurring.
There is a wide variation in the perception of the importance of disease-associated losses in aquaculture. Significant, avoidable, chronic losses are commonplace in nursery and carp-rearing farms in India. Most chronic losses are taken for granted, and their impacts are never assessed. There is, therefore, a need for better social and economic assessment so that the cost-benefits of alternative strategies can be evaluated. The stunted-yearling stocking practice could be one such alternative strategy to minimise the socio-economic impacts of disease on rural aquaculture. Better frameworks and methodologies should be developed for routine data collection on socio-economic impacts of aquatic animal diseases. It is essential to redefine some concepts like loss perception, disease-related loss, health management costs, externalities associated with diseases, and indicators of disease loss. Through co-ordinated efforts, it should be possible to assess and quantify the socio-economic impact of disease on rural communities dependent on rural aquaculture and culture-based capture fisheries. Such assessments would make primary aquatic animal health care a priority, and such a strategy would be more cost effective, focused and beneficial to rural aquaculturists.
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