Bangladesh is one of the highest populous country in the world, with its 132 million people in an area of 147,570 sq. Km, which represents an average density of 12 people for each hectare of land. Mainly due to the growing demand for the supply of animal protein, a number of fast growing exotic fish species. Exotic species is belonging by nature or origin to another part of the world, brought in form abroad or Foreign, or strange. Now 18 major and common exotic species are culture in Bangladesh. Various sources noted that the Tilapia (Oreochromis mossambicus) introduced in 1954 was the first exotic fish in the Bangladesh. They are maximum larvivorous fish.
Biodiversity is the basic boitic resource that sustains all human life- support systems on this cart. Continuance of rich biodiversity is an assurance for our survival. However, it is deckling rapidly and is a cause of alarm and distress all over the world. The impacts of the exotic species can be enormous, dangerous, irreversible and invariable. Invasive species are the agents of “species and biodiversity loss’ in ecosystems all over the globe. Alternation to ecological communities caused by alien invasive animal species influence the functioning and overall health of the affected ecosystems. Negative effects of biological invasion include fall in production and cost of controlling invasive. Here, Invasive species is an alien species which colonizes natural or semi-natural ecosystems, is an “agent of change and threatens native biological diversity”.
The overall guiding principles for the prevention, introduction and mitigation of impacts of alien species development by IUCN are based on the following :-
a. Precautionary approach as the pervading principle.
b. Sharing of relevant information.
c. Research and management of invasive.
Statement of the Problem
It is generally agreed that release of exotic fish creates competition with native species for space, food and other resources. The risks of irresponsible introductions of alien species to conservation of biodiversity include hybridization, habitat and water quality alteration, competition, predation and disease. The potential impact is far more serious is the exotic species can successfully reproduce and persist in the receiving environment. As examples, Tilapia are notorious for their prolific breeding while African catfish are known for voracious predation. These fishes can be expected to pose a high risk to some indigenous species due to their feeding, reproductive and life history strategies. However, the outcomes of an introduction are difficult to predict it is possible that they may coexist with indigenous species due to spatial or temporal variability in habitats or strategies for their survivability and existence. Successful introduction of an alien fish species is often difficult to achieve. Considerable technical expertise is often required and many attempts fail.
As a country of wetlands, Bangladesh is very rich in fish diversity. Even then, many species were indiscriminately introduced and these invasive species rapidly spread into the wetlands as “biological explosives” due to recurring flooding. This has caused 54 indigenous fishes to become threatened (IUCN Bangladesh, 1999) within a very short period of time. The long term and even short-term, adverse effects were not considered while introducing these invasive species., combating the invasive species in Bangladesh will be very difficult because of lack of awareness and proper initiatives. How ever, by influencing excessive harvest and discouraging cultivation of these species may reduce the impact.
This is why, Uncontrolled entrance of exotic fish in our country seems to me like a problem to me and I have made up my mind to perform the research work on entrance and environment of exotic fish.
Rationale of the Study
As a sub-tropical country, Bangladesh is exceptionally rich in biodiversity. Geographically, the country is located at the transition of Indo – Gangetic and Indo- Malayan sub regions between the Himalayas and the Bay of Bengal. We have almost all major types of Fauna characterized by high growth rate, high economic value high market demand etc.
Bangladesh has a rich natural fisheries resources in our inland water, which have been providing human nutrition for countries. Recent observations have revealed the existence of three ecological populations like C. catla a) one of which is oriented to zooplankton feeding b) The second to phytoplankton and c) The third to planktons in general. This finding is of great importance to fish culture as well as stocking reservoirs, beels, haors and baors where phytoplankton population dominates. More critical observations are likely to bring out similar ecotypes/ sub – species in other indigenous species as well.
It is very essential that these renewable aquatic renewable aquatic resources are developed and conserved for posterity and no hasty steps by way of introduction of exotic fishes is encouraged that may endanger these gene pools. Introduction exotic fishes is not likely to enhance fish production to any remarkable degree over and above, what is provided by indigenous fish stocks. – Further, Since many of the exotic species proposed for introduction have feeding habits similar to endemic commercial fish species, it would be difficult to forecast the possible ecological fail out that my follow including possible elimination or displacement of indigenous genetic resources.
This is why, the research work has been very logical and time befitting .
Objectives of the Study
The research work has been undertaken and conducted with a view to achieving the following objectives.
a) To determine the present status of Exotic Species in Bangladesh
b) To measure the impact of Exotic Species on the aquatic environment
c) To determine the interaction between exotic and indigenous fishes in Bangladesh
Limitations of the Study
The work entitled “A Study on the Impact of Exotic Fish Culture in Bangladesh” may claim of importance for discussion as time demands. It is a vast topic. It is very difficult to think of or write with this topic in a little manner.
Sufficient information from different sources could not been collected because of limitation of time. Besides, the study and query needed for it could not have been done in all respects on account of busy schedule and regular examination of NAEM.
Because of not having enough collection of dailies or periodicals in NAEM library in this subject and for want of time, sufficient current information could not be presented. In addition, no extra time and money were sanctioned for preparing Term Paper. This is why problems were to face in many cases to perform necessary function. So, although it was not possible to sketch the total picture, I tried heart and soul to prepare a beautiful and informative Term Paper.
Definition of Terms
Exotic fish is alien species which is not naive and belonging by nature or origin to another part of the world or brought in form abroad or foreign or strange . Exotic fishes is species, subspecies of lower taxon occurring as a result of human agency in an area or ecosystem .
Exotic Fish Culture
It is a process of cultivation in Aquatic Environment. When exotic fish is cultured in native aquatic environment of Bangladesh is called exotic Fish culture.
Indigenous fish is native fish of Bangladesh
Indigenous Fish Environment
Indigenous fish Environment means aquatic Environment & Fisheries resources of this aquatic environment of Bangladesh .
Biodiversity is the basic biotic resources that sustains human life-support systems on this earth (kim 1993).
Invasive species is an alien or exotic species which colonizes natural or semi- natural ecosystems is an agent of change and threatens native biological diversity, is an agent of change and the native biological diversity, which subordination the previously dominant species.
These are the agents of species and biodiversity loss in ecosystems all over the globe.
Review of related literature is an essential part of research work. It gives researchers good background information about the concern area of research field, that helps them identify a research program and conduct research smoothly. A good number of literatures have been reviewed in this regards and cited here in some extent.
Francois, R. and Shariful, I .A. 2004. reported the positive impact of exotic Fishes of Bangladesh. They mentioned the benefits of wise use of exotic species of silver carp, Grass carp and common carp to biodiversity in Bangladesh.
Ameen, M. 1999 mentioned Negative effects of biological invasion including fall in production (e.g. fishery) and cost of controlling invasive. These also mentioned the overall guiding principles for the prevention, introduction and mitigation of impacts of alien species.
Dr. A.K.M Nuruzzaman (1989)- reported the adverse ecological impact of exotic fishes in our precious waters and the advantages being rendered by exotic fishes, at the same time, can not also be over looked for our higher fish production.
The Introduced Exotic Species of the Bangladesh
Exotic fish introduction in Bangladesh have been assessed and a total of 54 known introductions of 18 species and strains have been listed. The list includes ongoing importation of exotic fish fry by the aquarium trade, for aquaculture without any quarantine nor professional control of the Ministry of Fisheries and Livestock, as the Ministry of Commerce is the license issuing authority. In the following paragraphs some details are shown on the introduction of exotic species to Bangladesh :
(i) The Tilapia
Several types of Tilapia are found in Bangladesh. The smaller, gray colored Mozambique Tilapia (Oreochromis mossambicus), the larger dark blue Nile Tilapia (Oreochromis nitoticus) which has a striped tail and the red tilapia which has been created by selective breeding. All of the Tilapia found in Bangladesh are native from Africa.
Mozambique Tilapia was First introduced in 1954 from Thailand for mosquito control But the native range of this pecies (Rahman, Ak 1989) is the lower zambezi river in east Africa. They feed on a wide variety of worms insects, plant animal materials including phytoplankton etc and tolerate high densities and endure poor environmental conditions .
Fig. no-: Nile Tilapia (Oreochromis nitoticus)
(ii) The Chinese Carps :
They are generally considered to include silver carp, Grass carp, Bighead carp and Black carp.
a) The Silver Carp (Hypophthalmichthys monitrix)
The native range of this carp is china and It was first introduced to Bangladesh in 1969 from Hong Kong (Rahman,1989). The median part of the body is wide, Silver carp is adapted to plankton feeding and feed from a primary production level. It’s shapes like that Hilsha Fish. the body covered with silver colored scale.
b) The Bighead Carp (Hypophthalmichthys nobilis)
The native range of Bighead carp is central & Soulthrn china. It was introduced to Bangladesh in 1981 from Nepal. It seems to lookthe silver carp. But Head is bigger than silver carp. It is zooplankton feeder.
c) The Grass Carp (Ctenopharyngodon idella)
The native range of the Grass carp is china. It was first introduced to Bangladesh in 1966 from Hong Kong. It has diversified food habits. It has specialized pharyngeal teeth for aquatic vegetation. It’s Head is bigger than body and body length is long ventrally covered with silver white scales and dorsally covered with blacking gray scales.
d) The Black Carp (Mylopharyngodon Piceus)
It was introduced in 1983 from china. It’s body is covered with hardy & Blackish scales Primarily a mollusk eater. It lives in open water areas.
(iii) The Common Carp
It is popularly known as carpio .There are many verities of common carp. But the most popular variety is the mirror carp (Cyprinus carpio). It was brought from Nepal in 1979.
(iv) The Thai Pangas ( Pangasius hypophthalmus)
It was introduced from Thailand in 1990 ( Rahman, Ak, 2003). But its native range is in the mekong and chrophyro. It is omnivorous in food habits.
(v) The African Magur (Clarias gariepinus )
It was introduced from thailand in 1990. It is an omnivorous fish with high tendency of predation. It is a very big sized and hardy cat fish .
(vi) Thai Sarputi (Puntius gonionotus)
It was brought in 1977 from Thailand. It has a resemblance with the local sarputi and may grow up to 20cm.
(vii) Nilotica (oreochromis niloticus )
It was brought from Thailand in 1974.
(viii) The Sucker Mouth Catfish (Hypostomus plecostomus)
It was brought from Thailand in 1980 for Aquarium use. It is a highly resistant fish .
Fig. no- : The Sucker Mouth catfish (Hypostomus plecostomus)
a) The Milk Fish (chanos chanas)
It was introduced by shrimp farmers of cox’s bazar are in 1995 , to substitute the losses caused by the outbreak of WSS disease.
b) The Red Piranha (Pigocentrus nattereri)
It was brought from Thailand in 2003. It has very sharp teeth like sickle. It is a dangerous species for the Genetic ecosystem.
Table- The list of common exotic fishes were brought into Bangladesh, their origin and year of introduction
|S.No.||Common Name||Name of species||Country of origin||Year of introduction||Objectives|
|1||Gurami||Trichogaster pectoralis||Singapore||1952||To control Insect & Aquatic Weeds|
|2||Tilapia||Tilapia mossambica||Thailand||1954||To control insect & remove Malaria|
|3||Scale carp||Cyprinus carpio var.communis||India||1960||For culture|
|4||Grass carp||Ctenopharyngodon idellus||Hongkong Japan||1966 1970||For culture & to control aquatic weeds|
|5||Silver carp||Hypophthalmichthys molitrix||Hongkong||1969||For culture|
|6||Nilotica||Oreochromis nilotica||thailand||1974||For culture|
|7||Thai Sarputi||Puntius gonionitus||Thailand||1977||For culture|
|8||Mirror carp||Cyprinus carpio var.specularis||Nepal||1979||For culture|
|9||Bighead carp||Aristichthys nobilis||Nepal||1981||For culture|
|10||Black carp||Mylopharyngodon piceus||China||1983||For culture|
|11||African magur||Clarias gariepinus||Thailand||1990||For culture|
|12||Thai pangas||Pangasius hypophthalmas||Thailand||1990||For culture|
|13||Sucker mouth cat fish||Hypostomus plecostomus||Thailand||1980||Use for aquarium|
|14||Monosex tilapia||Genetically Improved farmed Tilapia||Philippines||1994||For Research & Culture|
|15||Monosex Scale carp||Cyprinus carpio||Vietnam||1995||For research & observation under BFRI|
|16||Red Tilapia||Hybrid of albino||Liao & Chang||1988||For research & culture|
|17||Milk fish||Chanos chanos||Philippine||1996||For culture in water|
|18||Gold fish||Carassius auratus||Pakistan||1953||Use for aquarium|
Impacts of introduction of exotic fish
The rationale for introduction of the listed alien or exotic fish into Bangladesh was to augment fish production in the country as a means to increase the per capita fish consumption.
The positive and negative impact of Exotic fish on the indigenous species of Bangladesh are discussed on the following :
a) Tilapia and Nilotica
The arguments in favor of the introduction were:
i. They spawn in confined waters (i.e. ponds), annual stocking can be avoided.
ii. They are highly fecund and produce a large number of fry.
iii. They grow quickly, So, production is high.
iv They can be cultured in shallow, seasonal water bodies and ditches.
v. Said to be resistant to pesticides and other toxicants.
vi Tolerant to a wide range of temperature and salinity.
The arguments against are
- Their prolific breeding surpasses the carrying capacity of the learning to stunting of individuals.
ii. There are many indigenous species which grow in shallow, seasonal water bodies and ditches. These do not require annual stocking. They, in addition, control many pests.
iii That they grow quickly and the argument that tilapia production is higher is disputed and evidence is scarce (Ameen et al. 1984, Ameen 1985a, b; 1987).
iv. Population of many indigenous small fish species has declined due to the invasion of tilapia and Nilotica in our water bodies.
v. Comparative production: Ameen et.al. (1984) demonstrated that in mini ponds and small water body’s production of small indigenous fishes are at par with tilapia production.
vi. The consumable weight relative to total weight of indigenous fishes is higher than tilapia. Hard bony part is relatively high in tilapia. The soft bones of small
indigenous species are consumed and are source of nutritive vitamins.
Tilapia may be recommended for those areas where native species are scarce of absent, e.g., in countries like Israel. In a country like Bangladesh which is rich in fish biodiversity, introductions should be very restricted.
b) African Magur
Predation and voracity of this catfish is legendary. People do not like the meat of larger sized fish of this species, Now there are attempts to keep its size smaller for easy marking. Production per unit area of a carnivore is much less that a herbivore (theoretically as much as 80-90% less) from food chain computations/African magur escaped to the open waters during the floods and reported to have consumed even ducklings, let alone other fishes. This will lead to great reduction of population of the indigenous species, endangering their future existence. Therefore, increasing fisheries production to meet the national demand emphasis should be on the culture of dominantly herbivore species rather than on carnivores.
c) Chinese carps
i. Grows very fast, if provided with adequate grass and other vegetable food.
ii. May be used effectively for aquatic weed control.
iii. Its faucal matters manure ponds.
iv. Does not compete with other cultured species.
i. Scarcity of grass during dry months
ii. Competes with cattle in Bangladesh where natural cattle feed is in very short supply.
iii. Response to hypophysiation unpredictable.
iv. Apprehension of grazing on rice plants if escapes to open waters. (Corroborated by news of it destruction of paddy fields in media). However, cannot be a permanent -nuisance because the possibility of its breeding in natural waters of Bangladesh is negligible because of high ambient temperature.
d) Common carp
i. Breeds naturally in confined waters in Bangladesh conditions.
ii. Hardy and disease resistant.
iii. Release nutrient by turning bottom mud.
iv. P.G. is more potent and extensively used for hypophysation.
v. Suitable for cage and pen culture.
i. Destroys pond embankments, makes water turbid by turning up mud.
ii. Attains maturity early, thereby growth retarded
iii. Tend to study at high density.
iv. Eggs are easily infected by fungus.
v. Difficult to harvest with sheet.
e) Silver Carp
Fast growing, planktivore and does not breed in ponds. They are easy to harvest. Silver carp feed mainly on small phytoplankton, as small as 30-40 up, which Catla can not consume. Do not spawn in confined waters, but respond well to hypophysation.
i. Competes with Catla.
ii. Long distance transportation of fry needs special care.
At present the problem with silver carp to my experience, is stocking it in densities higher than its niche can support and the reedy putting Catla to necessary competition. The rate and ratio of different species in composite culture should be carefully assessed.
BANGLADESHI EXPERIENCES AND IMPACT OF USE OF EXOTICS
During last twenty years, the use of exotic species for aquaculture is significantly increased. During the same period the human population of the country is increased by about 62%, while natural fish habitat has been significantly reduced. This resulted an increased demand and price for fish, which led to overexploitation of natural fish stocks and increase of aquaculture activities. Introduction of polyculture techniques for maximum use of all available niches has caused the widespread utilization of fast growth exotic species, the Silver Carp and Grass Carp in particular.
Table- Proportion of Exotic Carps In Pond Production of Freshwater Fish In Bangladesh (1000 Mt)
|Total Exotic carp species||Silver carp|
Other exotic carps
|Total Endemic species|
Analysis of the data has shown an increasing proportion of the exotic species, during the period from 1993 to 2010. It is also found that the proportion of Catla has been reduced from 25.66 % in 1993-94 to 18.62 % in 2001-02, while that of the silver carp has been increased from 6.05 % to 24.65% in 1985-86 and 2009-10 respectively.
The reduction of Catla production might be due to three reasons: one is that the growth of silver carp is superior partic TB aneroid November to March when the growth of Catla is affected by low temperatures – which has motivated farmers to use higher stocking proportions of silver carp. The second assumption is that in Bangladesh, the food competition of silver carp to Catla has became greater than during its introduction to the country, because its feeding habit has been modified by genetic introgression from bighead carp. The third reason is that the production of regrettably introduced bighead carp – which is a strong competitor to Catla is escalating due to lack of awareness on proper polyculture practice among farmers. The bighead carp production is not distinguished from silver carp in the statistic and both are shown together as silver carp.
Research is systematic process. The essential step of a research work is to design the method, which will leads the researchers to conduct the research in proper way. For the methods in logical and scientific manner. The present study is on the study on impact of introduction of Exotic fishculture on the indigenous fishes Environment of Bangladesh Descriptive research method would be followed to perform the study .
Area of the Study
134th & 135th Foundation training courses of NAEM are my study areas. The Trainees of these courses have come from different government colleges of our country.
About 172 Teachers, are the sample population in this research area, who are taking training under these foundation training courses. Only 20 respondents within 172 trainees participated in this study.
Data Collection Tools
In research work data have been collected from two different sources – primary and secondary data.
The Trainees of Three courses are respondent group in this research work. open-ended and structural questionnaires are used in the study and recorded respondent’s answer. I also have to depend on secondary data mainly on journals, Research papers, publications, Books and also different websites . I have also been dependent on valuable advice from my supervisor.
Pertinent data were processed and transformed with the help of computer software, MS Excel in particular. Statistical tools and techniques were used for analysis and interpretation of data, statistical analysis was used for the purpose.
Analysis of Data and Findings
To find out the impact of Exotic fishes on the indigenous fishes Environment is the main study. Among 172 trainees, 20 trainees were interviewed. There is a brief discussion about the effect of Exotic fish and how to improve the cultivation process of the indigenous species. The discussion of the data analysis and finding is given in the following tables and is also shown using pie-charts.
Table – The Position of Fishes as the Animal Protein in Our Daily Meal
|The name of meal||Frequency||%|
Table- shows that highest percentage (60%) of respondent opined that fish is their main menu as animal protein in every days diet. On the other hand lowest number opined in favor of egg 0% .
Table – Knowledge About the Acceptance of Exotic Fish
|The type question|
Table -Most of the respondents are very much familiar about exotic fish (90%) but a negligible percent is Unfamiliar about exotic fish.
90% Trainees have knowledge about the acceptance of Exotic fish.
Table- Compilation About the Taste Between Indigenous and Exotic Fish
so much taste
In table- about 85% trainees supported the native fish. They are very much tasty meal.
Table – The Negative Impacts of Over Breeding of Exotic Fish on the Fish Food in Aquatic Environment
About 65% trainees declare that over breeding of exotic fish make the want of the fish food.
Table – The More Profitable Business Between Native and Exotic Fish Culture
|Type of fish culture|
|Native fish culture|
|Exotic fish culture|
Here 60% respondent trainees have been given answer with favor of the exotic fish culture. These are more profitable in fish market.
About 20 respondent trainees mentioned about the introduction of exotic fish as a dangerous species for aquatic environment . They agree with that Exotic fishes wastage fish food & contagion disease.
Table- Exotic Fish as Harmful Species for Local Biota
About 90% trainees mentioned that Exotic Fishes are harmful for local biota. 10% of them are not familiar about the concept of Exotic Fish, so they gave no opinion.
Results and Discussion
About 18 exotic species have been introduced in Bangladesh by Govt. or Non Govt. organizations. Silver carp, Thai Pangus and Thai Sarpunti are popular for the low market price. These exotic species are cultured extensionally in every area of Bangladesh. Respondent group said to forbid the cultivation of Piranha, sucker mouth cat fish etc.
The following information have been given the respondent group by discussion the questionnaire:
Tilapia (Oreochromis mossambicus) and Nilotica (O. niloticus) are likely harmful to biodiversity of indigenous fish environment, due to their ability to feed from a multitude of niches, subsequently competing with most native species for food, for habitat by their territorial characteristics, as well as reportedly feeding on young fish too.
Wise use of exotic species of Silver carp, Grass carp and Common carp can contribute to increase aquaculture production by utilizing vacant niches as phytoplankton, aquatic plants and benthos respectively. In addition, these exotics are able to fully utilize nutrients in the water during the cold period (November to February), when metabolism of endemic species are affected by low water temperature. Accordingly, growing period can be extended to full year. This can significantly contribute to food security of the country.
But the genetically eroded Silver carp represent and increased danger to biodiversity, as its competition for food to endemic species is high.
Clarias gariepinus and introduced Pangasius spp eat almost everything whichever they encounter. They not only feed on indigenous fishes and domestic ducklings but also on snails and birds that are killed and supplied by the cultivators.
Though many international conference and treaties as FAO Code of Conduct for Responsible Fisheries, Convention on Biological Diversity (CBD), WTO agreement on animal health and certification etc. have been held and these treaties have been given some recommendation regarding the Introduction and control of exotic species into any country. But these recommendations were failed.
In the following recommendations put forwarded on the basis of collected data in the study:
i. A website will conjunctively be open where elaborate information about the location, data, number and size of the exotic fishes entered voluntary or abruptly will be given by the support of FRSS and BFRI.
ii. Information on the biology of alien species and their probable impact on the indigenous biodiversity has to be evaluated on a pilot scale before listing as probable for introduction.
iii. Strict quarantine before entry into a new country / region.
iv. Dominantly herbivore species should get preference in selection for culture.
v. No pesticide should be allowed in any open water / natural aquatic ecosystems.
v. Indigenous species should be preferred for stocking and given similar treatments as given to exotics.
vi. The term “trash fish” in polyculture should be dropped. They should be included in the production system and not belittled,
vii. Rate of stocking should be appropriately revised according to the carrying capacity (enhanced due to inputs), which should be determined if not know already. (For details see Ameen 1984, 1993).
viii. The ratio of stocking surface, column and bottom feeders should be relevant to the natural carrying capacity of these niches. (For details see Ameen 1984, 1993).
ix. Utilizing a vacant niche by appropriate exotic species
x. Increasing exotic fish production in the introduced environment
xi. Filling environment, because of the absence of a similar desirable species in the locality transplantation.
xii. Not accompanying with pest, parasites or diseases such as “Ulcerative syndrome” which might attack native species.
It is quite unfortunate that long-term and even short-term, adverse effects were not considered while introducing these invasive species in Bangladesh. The excessive fecundity and growth rate of these species created pressure on the carrying capacity of the habitat, and the ecosystem balanced itself by reducing the indigenous species diversity and population. Even the grand economic balance concerning invasion was not properly assessed.
All over the world the invasive species have been identified as an agent of the loss of native biodiversity. According to Ameen (1999), alteration of ecological communities caused by alien invasive animal species influence the functioning and overall health of the affected ecosystems. Negative effects of biological invasion include fall in production of fishery and cost of controlling invasive.
Combating the invasive species in Bangladesh will be very difficult because of lack of awareness and proper initiatives. However, by influencing excessive harvest and discouraging the cultivation of these species may reduce the impact. No species should be introduced without evaluating their detailed life history, probable impacts and probable benefits in Bangladesh. No predatory species should be introduced. And lastly, people should be motivated to cultivate indigenous species. The indigenous species of an ecosystem evolves after a long history of evolutionary process. Hence, it is extremely inter-linked and balanced with all the local biotic and abiotic factors. The indigenous species is no way replaceable with the alien invasive.