Department of Aquaculture, Bangladesh Agricultural University,
Mymensingh 2202, Bangladesh
Hasan, M.R., and G.U. Ahmed. 2002. Issues in carp hatcheries and nurseries in Bangladesh, with special reference to health management. p. 147-164. 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.
The results of a case study carried out in 180 hatcheries and nurseries in northeastern and southwestern Bangladesh over a 30-day period during August-September 1999 are presented. The objective of the survey was to study different aspects of management issues in small-scale carp hatcheries and nurseries, with special reference to their health management. Three Indian major carps (rohu, catla and mrigal) and three exotic carps (silver, grass and common carp) were the dominant fish species cultured in most hatcheries and nurseries. The average production for spawn in hatcheries was 844 kg/ha, while in nurseries the production depended on the size of fry, the average production being 1.722 million/ha, 1.339 million/ha and 0.837 million/ha, respectively, for early fry, fry and fingerlings. Average survival of spawn, fry and fingerlings in hatcheries and nurseries was reasonably high, varying between 74-82%. The study indicated that the major source of spawn for nurseries was hatcheries, while hatchery broodstock were mostly collected from the farmers' grow-out ponds. In general, hatcheries were more profitable than nurseries. Profitability of nursery operations appeared to be vulnerable, due the high variability in market price of fry and fingerlings. Hatcheries and nurseries provided full-time employment to the farmers. The average contribution of aquaculture to the household income of hatchery and nursery owners varied between 79.3% (nursery owners) and 95.1% (hatchery owners). Although hatchery and nursery operations were often family activities, they also generated employment for hired labour.
The major management problems faced by hatcheries and nurseries were due to disease, drought and flooding. Diseases were less prevalent in hatcheries than in nurseries. The major diseases reported in nurseries were white spot, tail and fin rot, epizootic ulcerative syndrome (EUS), sudden spawn mortality, gill rot, dropsy and malnutrition, while the major diseases reported in hatcheries were sudden spawn mortality and fish lice. The economic loss due to disease was about 7.6% of the profit. Gill rot caused highest economic loss to affected farms, followed by sudden spawn mortality, fish lice, EUS and malnutrition. The results of this case study indicate that disease is an important issue in hatcheries and nurseries, although direct economic losses are not significant at this stage and hatchery and nursery operations are both profitable enterprises.
The contribution of fisheries to the gross domestic product of Bangladesh is 5.3% (M.R. Hasan unpubl. data). It is estimated that fisheries and its related activities support more than 7.0% of the country's population. The fisheries sector contributes about 6.0% of the export earnings, ranking third after jute products and leather. Fish account for about 6.0% of the per capita protein intake and contribute about 60.0% of the animal protein consumed throughout the country. The fisheries sector provides income for an estimated 1.5 million full-time and 11 million part-time fishers.
The inland-water resources of Bangladesh can be divided into the open inland waters, including rivers, streams, canals, estuaries, natural depressions (beels and haors) , Kaptai Lake and seasonal flooded lands; and the closed waters, including the ponds and tanks, baors1 and brackishwater shrimp farms. During 1996-97, 1.31 million mt of fish were produced; of which about 1.0 million mt were obtained from the inland waters, contributing about 79% of the total fish production.
The open-water capture fishery contributed about 58% of the total inland production, and the remaining 42% came from closed-water culture fishery. The production from culture fisheries has been increasing since 1983-84, and its annual growth rate over previous years has varied between 4 and 20%. The contribution of culture fisheries to inland fish production was 16% in 1983-84, which had increased to 33% by 1996-97. During the period 1983-84 to 1989-90, the average rate of decrease from capture fisheries was 1.7%/yr, although a trend of increasing fish production has been registered since 1991-92, probably due to the large-scale, open-water stocking programme initiated by the Government of Bangladesh.
The projected target for fish production during 2001-2002 is 2.08 million mt, and it is anticipated that this goal can only be achieved through intensification of aquaculture and probably, through enhanced fisheries from floodplains. Both the intensification of aquaculture and enhancement of fisheries through open-water stocking will, however, require a sustainable supply of large-sized quality fish fry and fingerlings.
Prior to 1990, most carp-seed production was derived from the collection of natural spawn from rivers. This situation was altered beginning in 1990, when a large number of hatcheries were established in different parts of the country. A comparison of spawn production from riverine sources and from hatcheries from 1988 to 1998 is presented in Table 1 and Figure 1. It is estimated that over 500 hatcheries have been established, and that they presently contribute about 97.6% of the total spawn production (Chowdhury 1999) (Tables 1 and 2). Of the total hatchery-produced spawn, 94.6% is contributed by private hatcheries and about 3.0% comes from public-sector hatcheries (Banik 1999) (Table 2). Therefore, the private hatcheries appear to play an ever-increasing role in fish production of Bangladesh.
1Beels are floodplain lakes, which may hold water permanently or dry up during the winter season; haors are depressions in floodplains located between two or more rivers, which function as internal drainage basins; while baors are oxbow lakes.
Table 1. Comparative status of spawn production from riverine sources and hatcheries in Bangladesh from 1988-98 (source: Chowdhury 1999).
Figure 1. Comparative status of carp seed production from riverine sources and hatcheries from 1988 to 1998.
Table 2. Status of spawn production from riverine sources and hatcheries
in Bangladesh during 1998 (source: Banik 1999).
A carp hatchery is generally considered as a facility for producing carp fry and fingerlings suitable for stocking in grow-out ponds. The carp hatchery, therefore, incorporates broodstock ponds, a hatchery (indoor facilities for fish spawning and egg incubation) and nursery ponds for raising spawn to fry, and rearing ponds to rear fry to fingerlings. Although many hatcheries have combined hatchery and nursery operations, others only produce spawn that is sold to the nurseries for production of fry and fingerlings. Fry and fingerlings are subsequently sold from the combined hatchery/nursery or from the nursery to the pond owners, either directly or via fry traders.
In recent years, a large number of nurseries have been established in different parts of the country, due to the growing demand of large-sized fry and fingerlings for stocking in grow-out ponds or in open waters. It is estimated that about 3 billion carp fry and fingerlings are produced in the country, whereas the projected demand of carp fry and fingerlings for aquaculture, culture-based fisheries and floodplain stocking is about 4.25 billion (Chowdhury 1999).
Aquaculture in Bangladesh is mostly carp-based; with Indian major carps (rohu, Labeo rohita; catla, Catla catla; and mrigal, Cirrhinus cirrhosus) and exotic carps (common carp, Cyprinus carpio; silver carp, Hypophthalmichthys molitrix; and grass carp Ctenopharyngodon idellus) being the main species cultured. The three Indian major carps and three exotic carps are also the main species so used in culture-based fisheries in oxbow lakes (Hasan et al. 1999) and in enhanced fisheries in floodplains through open-water stocking (Ali and Islam 1998).
Disease is one of the major constraints to intensification of aquaculture, and may eventually become a limiting factor to the economic success of the industry. In improved farming systems, nursery operators have a tendency to overstock fish, which ultimately causes disease. High stocking densities of fry and fingerlings during nursery operation generally increases stress, and subsequently, fish become more susceptible to infectious disease (Snieszko 1974). Fry and fingerlings are more susceptible to pathogens than are older fish because of their immature immune systems.
Parasitic diseases in nurseries are one of the most important factors limiting the growth and survival of fry and fingerlings. Gill myxoboliasis, caused by Myxobolus and Henneguya, has caused heavy losses in Indian major carps, mainly Catla catla, in Bangladesh. Hussain et al. (1994) reported that 61% of carp fry in nurseries of the greater Mymensingh District were infected with ectoparasites. The highest mortalities of carp fingerlings were due to the infection by Trichodina, Myxobolus and Dactylogyrus. Chandra et al. (1996) reported high prevalence of myxosporeans in juvenile Indian major carps (L. rohita and C. cirrhosus) in nursery ponds of Mymensingh. They reported severe gill infections caused by five species of the genus Myxobolus. Heavy mortalities of carp associated gill myxoboliasis have raised concern among Bangladeshi fish farmers (Chandra et al. 1996).
In Bangladesh, fry are also affected by gas bubble disease (Ahmed 1997), a result of water that is supersaturated with dissolved gases (N2 and O2). In hatcheries, the most serious diseases of eggs are caused by fungi (Saprolegnia and Achlya) (Ahmed 1997). Fry are also highly susceptible to microbial diseases.
Considering the important role of hatcheries and nurseries in providing a sustainable supply of quality fish seed for increased aquaculture and enhanced fisheries, a survey was initiated to study different aspects of management issues in small-scale carp hatcheries and nurseries, with special reference to health management.
This paper presents the results of a case study carried out in some selected hatcheries and nurseries in the northeastern (Mymensingh) and southwestern (Jessore) regions of Bangladesh. These two regions were selected because the concentration of hatcheries and nurseries in these districts is much higher than in other regions of Bangladesh. The study was carried out over a period of 30 days during August-September 1999 using a structured questionnaire. The draft questionnaire was prepared by the Network of Aquaculture Centres in Asia-Pacific (NACA) Secretariat. Prior to the actual survey, the draft questionnaire was field tested by the authors in few selected hatcheries and nurseries at Jessore and Mymensingh, and necessary modifications were made based on the feedback received.
The questionnaire was divided into two sections. The first section had six parts: general description, description of operation, revenue, cost of production, household information and problems occurring. The second section focused on specific disease problems, their economic impact and management interventions used to control disease. This section was used only when the farmers reported disease problems in their hatcheries or nurseries. The first section contained 74 questions, while the second section contained 29 questions. Except for requests for some qualitative information, all questions were multiple choice.
Altogether, 180 hatcheries and nurseries were surveyed (Table 3). Only private hatcheries and nurseries were surveyed; government hatcheries and nurseries were excluded from the study in consideration of the fact that 94.6% of the total spawn is produced by the private sector (Table 2). Data were collected by the enumerators directly from the hatchery/nursery owners using the questionnaire. Three enumerators were employed for Mymensingh region and two for Jessore region. The types of farm surveyed included hatcheries, nurseries and combined hatcheries and nurseries. Data were analysed from 174 of the 180 farms surveyed (six farms were omitted because information obtained from them was incomplete). A detailed breakdown of the types and numbers of farms analysed is given in Table 3. The information collected during the case study covers the period of one year from January-December 1998. Prior to the field-testing, background information on the number, location and distribution of hatcheries and nurseries was collected.
Enumerators tried to collect data as accurately as possible. However, in many cases, the farmers did not answer directly when they were requested to provide quantitative information and numerical figures for the revenues earned and the cost of production. For example, some farmers were unable to provide numerical figures for their total sales proceeds. In these cases, enumerators calculated the total sales proceeds from the quantity of fry and fingerlings marketed and the average sales price. Therefore, as these data were often derived from other related information and figures, in some instances, they may not be entirely accurate. Data were collected from the areas with the largest number of hatcheries and nurseries within both the Jessore and Mymensingh regions. Data collection is, therefore, somewhat biased and may not necessarily reflect the whole country. Nevertheless, the survey results should provide a precise picture of the status of carp hatcheries and nurseries, and reflect the relevant health management issues, as the farms were randomly selected from areas where the concentration of hatcheries and nurseries was highest.
Table 3. Type and number of farms analysed during the case study.
Altogether, data from 174 farms (90 from Mymensingh and 84 from Jessore) were analysed. Indian major carps (rohu, mrigal and catla), common carp, and Chinese carps (silver and grass carp) were the dominant species cultured in most of the farms at both Mymensingh and Jessore. The other Indian major carp (orange-fin labeo, Morulius calbasu) was cultured in 13 and 55 farms in the Jessore and Mymensingh regions, respectively. Apart from the Indian major and exotic carps, Java barb (Barbodes gonionotus) was the other dominant fish species cultured at the farms of Jessore (n=73; 86.9%) and Mymensingh (n=81; 89.0%). Kuria labeo (Labeo gonius), a minor cyprinid, was cultured in 47 farms at Mymensingh (51.6%). Other species cultured included sutchi catfish (Pangasius hypophthalmus), African catfish (Clarias gariepinus), black carp (Mylopharyngodon piceus), reba (Cirrhinus ariza), clown knifefish (Chitala chitala), bighead carp (Aristichthys nobilis), various carp hybrids and Nile tilapia (Oreochromis niloticus).
In Bangladesh, most intensive hatchery and nursery activities take place during June-December, although nursery activities often extend up to February. Generally, during or after February, farmers begin their pond preparation to start the new cycle of breeding and rearing. On average, the duration of the hatching cycle in hatcheries at both Mymensingh and Jessore was about five days and the number of cycles per year (June-December) was about 30. The hatchery cycle generally starts from the day when the broodstock are brought to the hatchery from the brood pond until the larvae absorb the yolk sac and the fry are transferred to the rearing pond or cement cistern from the hatching jar.
Nursery rearing of carp fry and fingerlings is generally carried out in three stages: a) early fry raising (spawn-early fry), b) fry raising (early fry-fry), and c) fingerling raising (fry-fingerling). The duration of the nursery cycle varies depending on the stage of rearing. The raising of early fry is, however, more common in Jessore, and the nurseries of Mymensingh generally do not produce early fry. The duration of the early fry-raising cycle varies between six to eight days, that of fry raising varies between 20-30 days, and that of fingerling raising between 90-100 days. On average, the total number of nursery cycles per year was 8-12. During early fry raising, spawn are raised up to 0.5-1.0 cm size; during fry raising, the fry are grown from 1.0 to 3.0 cm; while size ranges in fingerling raising vary widely between 3-15 cm.
Most hatchery and nursery owners in both the Mymensingh and Jessore regions had their own broodstock and nursery ponds. Many of the nursery owners also lease ponds from villagers. The study did not reveal any major difference in the number of ponds owned by the hatchery and nursery owners in these two regions. On average, the hatcheries had eight ponds with a total pond area of 2.06 ha, and the nurseries had, on average, seven ponds with a total pond area of 1.88 ha. Combined hatcheries and nurseries were larger, with an average of 10.5 ponds and an area of 6.74 ha.
Nevertheless, there was a large variation in total area between different hatcheries and nurseries. The maximum nursing pond area was 17.8 ha, and the minimum was only 0.06 ha. Forty-two percent of the nurseries sampled had a pond area of less than 1 ha. For hatcheries, the average area of ponds was 2.23 ha, with a minimum of 0.13 ha and a maximum of 9.93 ha. Forty-five percent of hatcheries had an area of less than 1 ha. For the combined hatcheries and nurseries, the average size was greater, with an average pond area of 6.74 ha. The maximum farm size was 43.71 ha, and the minimum was 0.82 ha.
The nursery owners were interviewed about their most likely sources of spawn
and the hatchery owners about the sources of their broodstock. The source of
spawn for nurseries was mainly from hatcheries (72.6 %); followed by wild caught
(e.g., river - 13.7%), own grown (12.6%) and other farmers (0.5%) (Table 4).
Similarly, the source of broodstock for the hatcheries was mainly from other
farmers' ponds (41.3%), followed by own grown (16.3%), wild caught (16.3%),
traders (11.5%), government and private hatcheries and other sources.
Table 4. Sources of spawn in the nursery and of broodstock in the hatchery
as reported in the case study.
In Bangladesh, the production of spawn is generally measured by weight, while the production of fry and fingerlings is measured by number. The average production from hatcheries and nurseries based on pond area was as follows: spawn 844 kg/ha, early fry 1.722 million/ha, fry 1.339 million/ha and fingerlings 0.837 million /ha.
Survival rates of spawn, early fry, fry and fingerlings in carp hatcheries and nurseries are given in Table 5. The average survival rates were higher for spawn (82%) and in fingerlings (81%) than for early fry and fry. The minimum survival for spawn, early fry and fry was 50%, and the maximum survival was 90-95%. There was more variation in the fry to fingerling stages, where survival varied between 20-97%.
Table 5. Survival rates (%) of spawn, fry and fingerlings in hatcheries and nurseries.
Fish spawn is generally sold by weight (kg), while fry and fingerlings are sold by number (thousands) in both Jessore and Mymensingh. Average prices for spawn, fry and fingerlings are shown in Table 6. Although there were variations in the price for different fish species, the information on average price was collected ignoring this species-wise variation. The average price of carp spawn was Taka 1154/kg, with the maximal and minimal price being Taka 1700/kg and Taka 750/kg. The average prices for early fry, fry and fingerlings were Taka 21, 112 and 1147 per 1000 individuals, respectively. There appears to be large variation in the minimum and maximum price of fry and fingerlings (Table 6). The minimum price of 1000 fry was Taka 40 and the maximum price was Taka 1000. Similarly, the maximum and minimum prices of 1000 fingerlings were Taka 3000 and 50. This shows that the market prices of fry and fingerlings were very much dependent on demand, and that the market demands are highly variable.
Table 6. Average price of spawn, fry and fingerlings in hatcheries and nurseries.
Average revenue, cost and profit with their standard deviations are shown in Table 7. The costs are highly variable, as is evident from their large standard deviations. In general, costs of operation are higher than preparation costs for all the three production systems studied. Although operational cost was lower for nurseries than for hatcheries and combined hatcheries/nurseries, the revenue earned and profit were also lower for nurseries than for the other two systems (Fig. 2). The average profit per ha water area was Taka 206,300 for hatcheries, while that for combined hatcheries & nurseries was Taka 142,300). The high variability in the market price of fry and fingerlings (Table 6) probably reflects the large fluctuation observed in the revenues earned by the nurseries. The average revenues for nurseries were Taka 172,200/ha.
Table 7. Revenue, cost and profit in hatcheries and nurseries.
Figure 2. Revenue, cost and profit in hatcheries and nurseries.
The average per caput income was highest in combined hatcheries/nurseries (Taka 78,746), followed by hatcheries (Taka 69,332) and nurseries (18,482) (Table 8). Although the average per caput income is reasonably high, especially for hatcheries and combined hatcheries/nurseries, the income is highly variable. The average contribution of aquaculture to household income is reasonably high, contributing from 79.3% (nursery) to 95.1% (hatchery). The contribution is, however, highly variable, especially for nursery and combined hatchery/nursery systems (see Table 8). The average number of persons in each household for the three systems varied from 7.5 to 10.
Table 8. Household income, percentage contribution of aquaculture in household income, and number of persons for different farm systems.
Apart from aquaculture, other economic activities of the farmers included paddy cultivation (most common), followed, in order of importance, by livestock raising, vegetable growing and fruit gardening. On average, the involvement of farmers in aquaculture was 9.7 yr. When farmers were asked to rank the reason for taking up aquaculture activities, 79.3% (138 of 174) responded that the cash income was the main reason, followed by employment (20.7%; 36 of 174). Few farmers ranked food, hobby or status as the main reason for their aquaculture activities.
The study also revealed that most of the hatchery and nursery owners are highly dedicated to their farming activities, as 170 out of 174 farmers (97.7%) responded that they spent most of their time in aquaculture as compared to other activities such as paddy cultivation, other crops, livestock raising etc. Farmers often share their farming activities with their wives and children (Fig. 3). Study of the breakdown of time spent by the family members of hatchery and nursery owners shows that the husband spent about 10.4 hr, followed by the children (6.6 hr) and wife (4.3 hr). However, hatchery and nursery activities may be comparable to a small-scale, rural agro-based industry, rather than with small-scale rural aquaculture. The use of hired labour is quite high (average 18.4 hr/day) in hatcheries and nurseries (Fig. 3). This shows that hatcheries and nurseries are generating some form of employment in rural areas.
When the farmers were interviewed about the sources or the agencies from which they learned about aquaculture, the majority responded that they learned the techniques from other farmers (28.6%) and neighbours (24.5%), followed by government training courses (21%). About a fifth of the farmers (19.7%) responded that they were self-taught. Government training courses appeared to have a much better extension effect in comparison to non-governmental agency (NGO) training courses (2.1%).
Figure 3. Breakdown of time (hr) spent by family members of hatchery and nursery owners.
Sound health management practice is a key to success in any hatchery or nursery
operation. In both the study areas, hatchery and nursery operators mentioned
several problems they encountered in their operations. When ranking problems,
51 farmers (29.3%) mentioned the occurrence of disease as their major problem,
while 48 (27.6%) ranked shortage of water was their major problem (Table 9).
Other problems faced by the farmers were flooding, theft and extremes of temperature
(too hot or too cold). In addition, some of the farmers mentioned lack of finance,
frequent hartals (general strikes) and bad road communication as their major
problems. Altogether, 118 (67.8%) and 133 (76.4%) of the farmers mentioned disease
and shortage of water, respectively, as one of their problems (Table 9).
Table 9. Ranking of problems faced by hatchery and nursery operators.
When ranking their problems, 118 farmers (67.8%) mentioned that they encountered diseases in their farms (Table 9). However, when specifically asked, 69% of the farmers said that they considered disease to be an important issue in hatcheries and nurseries. Disease was reported to be a more of a problem in the hatcheries and nurseries of the Mymensingh area, than in those of the Jessore area. The percentage of farmers reporting disease was 67%, 83% and 90% in hatcheries, nurseries and combined hatcheries/nurseries, respectively, in the Mymensingh area, while in the Jessore, area it was 61%, 54% and 0%, respectively. When the three production systems are compared, slightly more nurseries (72.9%) reported disease as one of their problems than did hatcheries (62.1%) or combined hatcheries/nurseries (66.7%).
The diseases reported were white spot (16.7%), tail and fin rot (16.3%), epizootic ulcerative syndrome (EUS) (12.9%), sudden spawn mortality (12.2%), fish lice (10.9%), gill rot (6.1%), dropsy (6.1%), malnutrition (5.4%), air gulping (4.1%), deformed larvae (1.7%) and others (7.5%) when the occurrence of disease in both study areas was combined (Fig. 4). As reported by several authors (e.g., Ahmed 1987, Hussain et al. 1994, Chandra et al. 1996), the diseases are caused primarily by parasites, fungi, bacteria and nutritional deficiency. However, in contrast to earlier reports, gas bubble disease of fry and fungal infection of carp eggs were not reported to be major problems in the hatcheries and nurseries covered in this survey. The occurrence of the most common diseases in the Jessore and Mymensingh regions is shown in Figure 5. Except for fish lice and white spot, the other diseases (e.g., tail/fin rot, gill rot and dropsy) were recorded in more farms in Mymensingh than in Jessore.
Figure 4. Occurrence of diseases (%) in carp hatcheries and nurseries.
Figure 5. Disease problems (number of farms) by region.
In Mymensingh, 40% of the farms (36 of 90 farms) reported sudden large-scale
mortality of spawn. The reason for this sudden spawn mortality was unknown.
Some of the farmers thought that a sudden sharp rise of water temperature in
hatcheries and nurseries might be the cause. However, many of the farmers observed
that sudden spawn mortality and the occurrence of deformed larvae are more common
for spawn produced late in the breeding season. Hatchery owners often produce
spawn three to four times using the same broodstock. Presumably, this practice
deteriorates the larval quality and eventually results in deformed larvae and
sudden mortality. Hussain and Mazid (1997) and A.S. Sardar (pers. comm.) reported
reduced growth rate, physical deformities, diseases and high mortality in hatchery-produced
carp seed, and they identified improper broodstock management, unconscious negative
selection of broodstock, unplanned hybridisation and inbreeding as the probable
reasons behind this reduced performance. EUS, sudden spawn mortality and malnutrition
were not reported in Jessore. As commercial hatchery and nursery activities
started much earlier there than at Mymensingh, this difference may be due to
better experience in farm management by the farmers of Jessore.
When the occurrence of the most common diseases was compared by system (e.g., hatchery, nursery and combined hatchery/nursery system) (Fig. 6), there are, in general, more problems reported in nurseries, followed by combined hatcheries/nurseries and then hatcheries alone. An exception was recorded with fish lice (argulosis), which is slightly more prevalent in hatcheries. In both the hatcheries and nurseries in both the study areas, diseases occurred more frequently during the hot season (April-May), followed by the rainy season (June-July) and then the winter (December-January).
Figure. 6. Disease problems (number of farms) by system.
One hundred and sixty-six of 174 farmers responded that they had faced disease outbreaks in their farms. When asked if they had ever attempted to treat their fish during an outbreak of disease, nearly all farmers (97.0%, 161 of 166 responses) replied that they had used some form of treatment. Most of the farmers of both the study areas attempted preventive and curative treatment measures, and only a negligible percentage of farmers (1.2%) harvested and marketed their products. A few farmers (1.8%) did nothing during disease outbreaks in hatcheries and nurseries.
Farmers in both study areas used different treatments such as chemicals and antibiotics, water exchange and manipulation of feeding and fertilisation. Use of chemicals ranked highest (98.1%, n=158), followed by stopping of fertilisation (31.7%, n=51) and feeding (28.6%, n=46), water exchange (27.3%, n=44) and use of antibiotics (15.5%, n=25). Insecticides and pesticides are often used for chemical treatment e.g., sumithion and malathion are commonly used to treat against fish lice on broodstock. Fifteen percent of the farmers had complete recovery from diseases as a result of treatment, whereas 31% had usually had recovery, 59% sometimes had recovery, and 4% never had recovery. Farmers engaged in hatchery and nursery businesses appeared to be well informed about their problems, in comparison to farmers engaged in other aquaculture activities. Most of the farmers have a good understanding of the diseases problems, and apparently, most (87.7%, n=142) have the ability to recognise some of the diseases, while 16 farmers (9.9%) reported that they were able recognise most of the diseases.
The impact of disease in hatcheries and nurseries was measured by fish mortality, economic loss, and also, if the farmers had changed their attitude due disease problems. In most facilities (66%), diseases caused partial loss of fry and fingerlings; only 7% of hatcheries and nurseries reported total loss of their stock, while 27% of the farmers reported no loss due to disease. For individual disease outbreaks, farmers reported varying losses. In hatchery and nursery operations, the following average mortalities were reported: malnutrition (55%), air gulping (43%), dropsy (42%), EUS (39%), sudden spawn mortality (38%), gill rot (34%), tail & fin rot (34%), argulosis (23%) and white spot (21%).
Ninety-one percent of the farmers (n=149) reported reduced fish price at the market and a subsequent reduction in household income as an impact of disease. A certain number of farmers (64 of 149) reported that an increase in debt resulted from disease outbreak, although this appears not to be a major impact of disease. Although disease was one of the major problems in hatcheries and nurseries, most farmers expressed their desire to continue aquaculture. There was no evidence of any change of attitude to aquaculture, and no farmers stopped aquaculture or changed species.
The economic losses reported by the farmers due to disease are presented in Figure 7. Gill rot caused highest losses, followed by sudden spawn mortality, fish lice, EUS and malnutrition. Other diseases causing considerable economic losses were tail/fin rot, dropsy, red spot, air gulping and white spot.
The average economic loss from diseases on those farms reporting disease was Taka 8062/ha/yr. However, the extrapolated loss for all 174 farmers included in the study was Taka 6275/ha/yr. The reported cost of treatment in hatcheries and nurseries was Taka 1669/ha/yr. The average profit was Taka 104,575/ha, and the loss due to disease was approximately 7.6% of the profit.
A majority of the farmers (57.7%, 75 of 130) contacted a government extension officer for help, guidance and suggestions when their hatcheries or nurseries had a disease outbreak. Farmers also contacted other hatchery owners (52.3%, n=68), other farmers (44.6%, n=58) and drug and chemical salesmen (11.5%, n=15). Apparently, the government extension officers provided the most useful information (42.3%, n=55) followed by other hatchery owners (27.6%, n=36), other farmers (16.9%, n=22) and drug and chemical salesmen (6.2%, n=8).
Figure 7. Reported economic loss of the farmers due to different fish diseases for affected farms.
This study was carried out with financial assistance from the Network of Aquaculture Centres in Asia-Pacific (NACA). The authors are grateful to M.J. Phillips and R.P. Subasinghe, and Mr. Ian MacRae for their help during data analysis and manuscript preparation. We acknowledge the help of the district and thana-level Fisheries Extension Officers of Mymensingh and Jessore, and particularly, that of Md. Abdul Khaleque, Project Director, Mymensingh Aquaculture Extension Project, for providing information on the number, location and distribution of hatcheries and nurseries. The kind help of the hatchery and nursery owners/operators in providing their data for this study is gratefully acknowledged.
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