1School of Life Sciences, Napier University
10 Colinton Road
Edinburgh EH10 5DT
Scotland, UK
2CARE Bangladesh
65, Road 7/A, Dhanmondi
Dhaka 1209, Bangladesh
3DFID Fisheries Management Support
House 42, Road 28, Gulshan
Dhaka 1212, Bangladesh
MacRae, I.H., G. Chapman, S.M.N. Nabi and G.C. Dhar. 2002. A survey of health
issues in carp/Macrobrachium culture in rice fields in Bangladesh. p. 95-112.
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.
During July and August 1999, a survey was conducted involving 105 farmers culturing giant freshwater prawn (Macrobrachium rosenbergii), locally known as "golda," and carp in "gher" (modified rice fields with high, broad peripheral dikes) in southwestern Bangladesh. The survey gathered information on the socio-economic circumstances of the farmers, their farming practices, and their perception of disease and its affect on their livelihoods. Information was also gathered regarding the farmers' response to disease, treatment and prevention, and sources of information and assistance. If specific diseases were reported, further information was gathered regarding impact, response and outcome.
The conditions reported as disease by the farmers mainly occurred late in the culture cycle when conditions were poor and the prawns were territorial, resulting in damage from fighting and subsequent infection. The response to disease problems was generally application of chemicals, with little understanding of their effectiveness, when better results might have been obtained by changes in management practice. Much of the advice received by farmers was from feed and chemical sales persons, whose advice may have been biased, and which generally involved the sale and application of chemicals. Advice from non-governmental organisations (NGOs) and Government Extension Officers ranked low in comparison, indicating that efforts were required to increase their profile in this area; which would hopefully reduce the input of ineffective chemicals and so reduce farmers' costs. Farm record keeping was not common, and encouragement of this by the CARE GOLDA Project is seen as a strategy that will lead to better management. Farmers' expectations were generally unrealistic, leading to poor management decisions.
"Gher" are modified rice fields with high, broad peripheral dikes. They are found throughout southwestern Bangladesh in areas that are seasonally or perennially inundated. The word "gher" literally means perimeter. A trench dug inside the dikes is designed to retain water in the dry season, while the high dike protects the gher from flooding during the summer.
During the rainy season, the entire rice field, which is generally not planted, is used for the cultivation of giant freshwater prawn or "golda" (Macrobrachium rosenbergii), a species native to Bangladesh, and fish. In the dry season, however, boro rice is planted and only the trenches are used for fish and prawn cultivation. At all times of year, the dikes can be used for growing vegetables, fruit, wood and fodder.
Since 1991, the expansion of gher operations has been huge, with the focus of this farming system being the prawn component. Little emphasis has been given to rice, fish, and the cultivation of fruit and vegetable crops.
The production of golda in Bangladesh is still dominated by very small producers, typically farming less than one acre, producing a crop that is sold on the international market. In southwestern Bangladesh, vulnerable farmers routinely take out huge loans in order to stock their gher with M. rosenbergii. The potential for high profits has drawn farmers into the practice; however, largely because of the loans, increasing input costs, uncertain markets and natural disasters, their exposure to risk has increased dramatically. By diversifying production components and thereby, reducing investment in the Macrobrachium component, and improving household financial and gher management skills, the CARE Greater Options for Local Development in Aquaculture (GOLDA) Project aims to reduce the vulnerability of gher households.
The project, funded by The Department for International Development, United Kingdom (DFID), began work with 30,000 marginal and vulnerable farmers in 1996, to diversify and stabilise their gher systems to decrease exposure to risk. A major aim of this project is to increase the ability of these farmers to make more informed decisions in order to make their systems sustainable. This survey examines the risks that aquatic animal disease pose to these already vulnerable households.
The objective of the survey was to collect information on the impact of disease on production of Macrobrachium/carp farming in ghers; the species of carp stocked in the ponds are silver carp (Hypophthalmichthys molitrix), catla (Catla catla), rui (Labeo rohita) and grass carp (Ctenopharyngodon idellus). A survey questionnaire was prepared and a survey carried out over a period of three weeks between 2 and 23 August 1999 in 12 thana in five districts of Bangladesh. The survey form was in two parts. The first part gathered data on the socio-economic circumstances of the farmers and the production techniques that are employed. Some questions related to health issues, management, knowledge and contact with extension services and other forms of assistance; the initial form contained 64 questions. If specific diseases were mentioned, the second part was completed, which contained questions relating to occurrence, frequency, farmers' perceptions and knowledge of disease, treatments applied and types of assistance available. One hundred and five forms were completed.
In the limited time available, the forms were not adequately tested and some difficulty was subsequently encountered in the analysis of the data. Had time been available, a pre-survey would have been useful to establish likely responses to questions, and so allow better construction of the survey and easier analysis. In addition, many farmers were unable to state the costs and amounts of farm inputs or to to describe the clinical signs of disease. Many farmers were also reluctant to respond to the questionnaire.
Of the 105 farms surveyed, all were gher farms growing M. rosenbergii and carp.
The average age of the farms was 4.8 years, with the oldest being 15 years and
the newest being one year old. The growth in gher farming among the farms surveyed
is shown in Figure 1.
The total water area of the farms varied from 0.04 ha to 1.31 ha, the average
being 0.36 ha. The majority of the farms utilised all available water area.
Thirty-one farms utilised part of the farm as a nursery, growing the prawns
from an average of 0.55 cm to an average of 3.53 cm. All fry were wild caught,
although a large percentage (90%) was obtained from fry traders.
Details of family size, general income and income from aquaculture are given in Table 1. It should be noted that 79 respondents (77%) reported a daily per capita income of less than US$1.
There was a wide range of experience in aquaculture, with the maximum time
involved being 35 years. The minimum was two years and the average was 5.8 years.
The majority of the farmers (81) stated that they learned aquaculture from other
farmers; 42 learned from friends and neighbours, 24 were self taught, five learned
from Government Extension Officers and four learned from non-governmental organisations
(NGOs).
Table 1. Household size and income.
The majority of farmers grow prawns for income. The only other first-ranked reason was status (9 responses). The second-ranked response (79) was for food; however, it is likely that this refers to the fish that are also grown in the ponds. Interestingly, the third-ranked reason was status (27 responses).
The other main activity that supports the family was rice growing on their own farm. Fruit and vegetable growing on farm and fruit growing off farm are important secondary activities. Labouring off farm and raising livestock, both on and off farm, were also important.
The two major activities of the household are aquaculture and rice growing, with the majority of the time spent on aquaculture. Other activities, including business (16), service (10), betel farming (7), sugar cane (4) and van driving or pulling (3), were also significant to the household. The husband spent more time per day working in aquaculture activities (average 4.8 hr/day) than the wife or children (average 1.1 and 1.6 hr/day, respectively). Other labour averaged 2.3 hr/day.
Production and operating costs are given in Tables 2 and 3.
Table 2. Production costs.
Table 3. Operating costs.
As can be seen from Table 4, the farmers' expectations of profit and yield for both carp and prawns were much higher than that realised. Expected profit from prawns ranged from US$469 to 24,160, the average expected profit being US$4,749. A similar picture emerged for carp. Of the 105 farmers interviewed, only two achieved more prawn production that they had expected, whereas seven farmers exceeded expectations with carp production.
Table 4. Production against expectation.
When farmers were asked if the crop did as well as expected, 90% of them indicated that they were disappointed (Table 5). This might indicate that farmers have unrealistic expectations.
Table 5. Farmers' expectations.
When production is graphed against expectation, the shortfall is quite clear
(Figs. 2 and 3).
Figure 2. Expected and actual prawn production.
Figure 3. Expected and actual carp production.
Reported survival rates are given in Table 6, along with prices for carp and prawns.
Table 6. Survival rates (%) and prices (US$) for carp and prawns.
Farmers were asked to rank, in order of significance, the problems that they encountered (Table 7). The major problem was flooding, followed by too little water. Disease was ranked third. Theft figured highly in the second ranking.
Table 7. Problems encountered by farmers.
Farmers were asked what they thought about aquaculture; responses are presented in Table 8. Although farmers acknowledged that aquaculture is a risky business, they still considered it to be profitable and to have a high status. Disease was also seen as an important issue.
Table 8. Farmers' perceptions of aquaculture.
The majority of farmers (94) said that they were able to choose fry, and the majority (94) also considered that the fry were healthy. Three farmers considered that the fry were not healthy and seven did not know.
Of the 105 farmers interviewed, 42 reported that they had experienced disease
problems in the last year, three said that they had problems in the last four
months, and four said that they had problems in the last eight months. The outcome
of the majority of the problems encountered was that "some" of the
prawns or fish died; only two farmers reported that "all" the prawns
or fish died. The significance of disease to the household, as felt by the farmers,
is given in Table 9.
Table 9. Economic result of problems.
Table 10. Pattern associated with disease.
Farmers were asked if the occurrence of disease changed their attitude to aquaculture. Responses are summarised in Table 11.
Table 11. Summary of farmers' responses to the question "Did the problem
result in a change in attitude towards aquaculture?"
When farmers were asked if they contacted anyone when they had a problem, 38% said that they did. The majority (31) contacted other farmers for information, 10 contacted feed salespersons, six contacted Government Extension Officers, five contacted drug and chemical salespersons, and five contacted NGOs. When requests for assistance were made, 34 farmers said that response was prompt, three said that it was slow, and one farmer said that no response was received.
Other farmers were considered to be the most useful source of information, with CARE Bangladesh the second most useful source. Friends and neighbours were also considered good sources of information, while Government Extension Officers ranked fourth.
Farmers were asked about their ability to recognise disease. Forty-six farmers said that they could recognise some diseases, and 12 said that they could not recognise any diseases. Only one farmer said that he could recognise all diseases, and two said that they could recognise most diseases. The ability to recognise that disease was present was based on a number of factors, the most frequently cited being reduced growth, although mortalities, abnormal behaviour and abnormal appearance were all only slightly less significant.
When farmers were asked what they did in response to disease, 38 said that they would attempt treatment, 19 said that they would conduct an emergency harvest, five would do nothing, and three would seek help. If treatment was attempted, it was generally involved the use of chemicals (35 of 41 responses). Two farmers would use antibiotics, two would change water, one would stop fertilising and one would stop feeding. When asked where they learned about this treatment, the majority (25 of 36 responses) said that they learned from other farmers. Eight learned about the treatment from feed salespersons and three learned from drug and chemical salespersons. The average cost of the treatments applied was US$5.30, the maximum was $20.60, and the minimum was $0.22. Eighteen farmers said that the treatment was "sometimes" successful, eight said that it was "usually" successful, eight that it was "never" successful, and only seven said that it was "always" successful.
Three of the most common diseases described are antenna and rostrum rot; jatha - infection and ulceration of the antennae that may eventually spread to the head; and dhari jhara - removal of the rostrum. These three conditions may possibly be the same problem. Other diseases reported include karat baka or curved rostrum, which may also lead to head ulcers; shuga or sponge rog, a syndrome in which affected prawns become shrunken and hard, with the flesh shrinking away from the carapace; and shadla pora - external fouling and softening of the muscle resulting in poor growth and failure to moult, said to be due to malnutrition.
Black gill disease, generally caused by precipitating nitrogenous wastes in ponds with high levels of ammonia and nitrite, usually occurs towards the end of the growing cycle when the water quality has deteriorated. The only remedy is to change the water.
Epizootic ulcerative syndrome (EUS) is a seasonal (winter) epizootic condition of freshwater and estuarine fish characterised by the presence of the invasive fungus Aphanomyces invadans, typically leading to a granulomatous response. There are a large number of ulcerative conditions of fish, and EUS can only be positively confirmed by histological examination. Chinese carps appear to be unaffected by EUS, and Indian major carps may suffer large mortalities as fingerlings; however, larger fish, although they are ulcerated, do not die in large numbers. Four farmers reported EUS in Hypophthalmicthys molitrix, Catla catla, Barbodes gonionotus, Cirrhinus cirrhosus, Mugil sp. and Labeo rohita. The fish were around eight months old, and two of the farmers reported that the problem was caused by cold weather. There is no remedy for EUS, other than to prevent the incursion of wild fish that are carriers.
Tail rot in prawns is a condition that also arises from initial infection and ulceration exacerbated by poor pond conditions or aggressive behaviour.
A breakdown of the problems encountered by the farmers is provided in Table 12. Most of the problems occurred towards the end of the growing cycle (the average for all diseases reported was 237 days and the minimum was 60 days). This would be at the period in the grow-out cycle when the prawns are at their largest, the water conditions have deteriorated, and the stocking densities are at their maximum. All the problems appear to be associated with poor pond conditions, lack of food or the aggressive behaviour of large prawns. Farmers should consider harvesting earlier, as the pond conditions begin to deteriorate.
Table 12. Frequency of disease.
The diseases did not seem to cause catastrophic losses, most farmers reporting
that only a few animals died. There were, however, three reports of total loss,
one from dhari jhara and two from "virus." In terms of overall loss,
this may not appear to be a major problem; however, it would have had a significant
impact on the livelihoods of the three farmers involved. It is possible that
the farmers were relating their problems to viral diseases of marine shrimp,
such as white spot disease and yellowhead disease, which do not affect Macrobrachium.
Losses are measured by mortalities, and it is not possible to estimate the loss
of production due to reduced growth. The various causes of disease, according
to the farmers, are listed in Table 13.
Table 13. Cause of disease.
A diverse number of treatments were reported, many involving multiple combinations of chemicals. Liming was the most common treatment applied (20 specific cases, 15 in combination with others), and Aquanourish was common in combination. Potassium permanganate, potash alum, silica powder, Aquaclean and methylene blue were also cited as treatments. In an attempt to assess the value of these treatments, more information was sought on the dose rates, frequency of application and their relative merits (see Table 14).
It was not possible to find out the active ingredients of the proprietary chemicals Antibacter, Y Organ, Aquanourish and Molt-7; however, if the gher is at least one metre deep, Antibacter, Y Organ and Molt-7 are employed at doses that equate to 0.65 ppm. It is unlikely that any proprietary chemical will have a significant effect at this concentration. Aquanourish is used at a rate of 22.5 ppm; however, as the ingredients are not known, it is difficult to make an assessment. As it is used to improve water quality and may be a fertiliser, it is possibly no more useful than urea or TSP and is a little more expensive. In general, it is best to exclude any substance from a pond unless its constituents and potential effects are known.
Copper sulphate, generally in the chelated form, is used at a rate of 0.25 ppm to induce moulting. Higher doses are used to control algae and plankton; however, these treatments must be followed by water exchange. Copper sulphate is very toxic, and there is a narrow range between its effective treatment dose and the dose that will be toxic to animals. Toxicity varies with alkalinity of the water and is higher at low alkalinity. In water of high alkalinity, the effectiveness of copper sulphate treatment will also be greatly reduced.
Methylene blue is reportedly used at a rate of 1.25 to 2.5 ppm. It is often used for the treatment of aquarium fish at doses ranging from 1-2 ppm as prolonged baths, to 8-10 ppm as short baths; however, its efficacy in pond situations is uncertain.
Table 14. Merits and costs of treatments.
Potassium permanganate is used at a rate of 50 ppm, and in the highly organic
environment of these ponds, is likely to be inactivated very rapidly after application.
As an indication, the effective dose for treatment of fungus is 75 kg in a 1,000
m2 pond; this is 25 times the dose rate used by the Macrobrachium farmers. To
be used effectively to oxidise organic matter in the pond, the potassium permanganate
demand (PPD) must first be calculated, and a dose rate 2-3 ppm greater than
that should be used for treatment. High dose rates will also lower dissolved
oxygen and may produce a toxic end product, manganous dioxide, from the reaction
with organic material.
Farmers generally use two or more chemicals at a time for any disease problem, according to the recommendation of chemical suppliers. There is very little evidence of recovery from diseases after application of these chemicals.
Liming was the most common treatment used and was reported to be "sometimes successful" by 11 farmers.
The majority of farmers (28) learned about the treatment that they used from other farmers. Feed salespersons (7) and NGOs (5) were also a source of information, while chemical salespersons (4) and government extension services (3) were less frequently consulted. Five farmers reported that they learned the treatments themselves.
When farmers were asked when diseases were last seen, they indicated that the majority of diseases occurred within the last year (Table 15).
Table 15. When disease was last seen.
When asked how often these diseases were seen, the farmers responded that most were seen every year, but not more frequently. When asked when in the growing cycle the disease occurred, they responded that there was no distinct pattern of occurrence; however, as can be seen from Table 16, the dry and wet season was cited as the most likely time for disease to occur.
Farmers were asked if they lost production due to disease; responses are given in Table 17.
Table 17. Loss of production and additional inputs due to disease.
Farmers' estimates of the value of lost production and the cost of additional
inputs to control disease are given in Tables 18, 19 and 20.
Table 18. Value of lost production.
Table 19. Cost of additional inputs.
Table 20. Loss of income in relation to household income.
Farmers were asked if they would eat fish or prawns from a pond with sick fish or prawns; 40 replied that they would and 18 replied that they would not.
In order to examine the impact of disease on individual farmers, two case studies
were extracted from the data (see Boxes 1 and 2).
|
Box 1. Case Study 1: Mr. Ratan Kumar Roy of Miximil Village Mr. Ratan Kumar Roy of Miximil (Khya Ghut) Village, Khulna District, has been farming Macrobrachium in gher systems since 1996 and has four years experience in aquaculture. The total water area of his farm is 0.57 ha, and he also stocks Catla catla, Ctenopharyngodon idellus and Hypophthalmichthys molitrix. Mr Roy's family consists of six members, and their family income is US$1,650.00, 68% of which ($1,122) comes from aquaculture. He adopted aquaculture because he saw it as a way out of indebtedness; he also relies on business for income. He learned to farm Macrobrachium from an NGO and from his neighbours, and believes that aquaculture is profitable but risky. From the last crop that he farmed, he expected to harvest 865 kg/ha prawns (493 kg), but he did not estimate the likely carp crop. He actually harvested 343kg/ha (196 kg) of prawns and 25 kg of carp. He said that the crop had not done as well as expected. The estimated survival rate was 36% for the prawns and 45% for the carp. Mr Roy had expected a profit of US$618. Although he sold his crop for an average of US$5.67/kg ($1,111), he also spent $577 on feed, $226 on seed, $38 on liming and labour for pond preparation, and $54 on other costs. This left him with a profit of US$216. Mr Roy said that disease was the number one problem, and that his farm suffered from four disease problems during this period, antenna or rostrum rot (estimated losses of 5%, US$4.60); "jatha" (estimated losses of 4%, $20.00), "shadla pora" (estimated losses of 1%, $10.30); and black gill disease, the most serious of the problems, which caused estimated losses of 50%, valued at $1,111. Mr Roy's total losses amounted to 60% of the crop and a total estimated value of US$1,145. This amounted to about 67% of Mr Roy's family income. Also, he spent an estimated US$309 on unspecified disease control measures. Mr Roy says that he is unable to identify specific diseases, but can recognise problems when there are mortalities, abnormal appearance or reduced growth. He believes that bad management caused the black gill disease, virus caused the rostrum rot, bad food and excess mating caused the jatha, and drought caused the shadla pura. Mr Roy says that these diseases resulted in reduced price, reduced income and increased debt for his family. It did not change his attitude about aquaculture, and he will continue to farm. |
|
Box 2. Case Study 2: Mr. Hari Dash Mandal of Shahera Village. Mr. Hari Dash Mandal of Shahera (East) Village, Bagerhat District, has been farming Macrobrachium in gher systems since 1987 and has 13 years experience in aquaculture. The total water area of his farm is 0.37 ha, and he also stocks Labeo rohita, Catla catla, Cyprinus carpio and Cirrhinus cirrhosus. Mr Mandal's family consists of six members; their family income is US$1,026 and 16.6% of this ($170) comes from aquaculture. Other income is derived from unspecified business. He learned to farm Macrobrachium from a relative and from a neighbour and believes that aquaculture is profitable but risky and that disease is a problem. From his last crop, he expected to harvest 543 kg/ha prawns (200 kg) and 543 kg/ha (200 kg) carp. He actually harvested 47 kg/ha (17.2 kg) of prawns and 162 kg/ha (60 kg) carp. He said that the crop had not done as well as expected. Survival rates were estimated at 63% for the prawns and 75% for the carp. Mr Mandal had expected a profit of $1,030. He sold the resulting crop for an average of US$7.22/kg ($124). He spent $14 on feed, $151 on seed and $22 on other costs. According to these figures, he incurred a loss of US$63. Mr Mandal said that disease was the number one problem, and that his farm suffered from a single disease problem during this period, shuga or sponge rog, that accounted for estimated losses of 5% (US$50.52). This disease occurred when the prawns were around 285 days old. This accounted for an estimated 4.9% of Mr Mandal's family income. This disease alone would not account of the lost production reported by Mr Mandal, and this is not explained. Mr Mandal says that he recognises some diseases and can recognise sickness when there are mortalities, abnormal appearance or reduced growth. He believes that bad food and too little water caused the disease. He reports that he sees this disease every year at the dry season and just before harvest. Mr Mandal contacts a relative if he has problems, and this is the person whose advice he relies on most. Mr Mandal says that disease resulted in reduced price and reduced income, but no increased debt for his family. As a result of these problems, Mr Mandal has stopped promoting aquaculture. |
Farming Macrobrachium is a risky practice, a fact that the farmers largely acknowledge; however, they also see it as being potentially very profitable. By borrowing money to stock Macrobrachium, already vulnerable farmers are putting themselves at even greater risk. Given the farmers' intentions to continue prawn/fish aquaculture, even those farmers who sustain significant losses, the strategy of crop diversification being promoted by GOLDA is essential. In addition to this, there are some other lessons to be learned from this study:
The authors thank Reshad Alam and the field staff of the CARE, GOLDA Project
for their assistance, and the Department for International Development (DFID)
for financial support.
