Although alien invasive fish species like Piranha has been banned in Bangladesh, farmers in different regions of the country still continue to culture this species as they lack knowledge on the destructive role of this fish. Also, general people are buying this fish for consumption as they also do not have appropiate knowledge. In this regard, I am posting the article below to get ideas about the alien invasive species, their destructive roles and their management.

 ALIEN INVASIVE SPECIES: A THREAT TO FISHERIES BIODIVERSITY

The Daily Star , Page‐16 (Environment), Dhaka Friday March 2, 2007.

Alien Invasive Species is comparatively a new term in biodiversity and this term is now being frequently used in different scientific workshops, seminars and roundtable discussions. Before proceeding to the brief discussion on Alien Invasive Species, let’s know the definition which is defined as “an alien species (a species, subspecies, or lower taxon, introduced outside its natural past or present distribution; includes any part, gametes, seeds, eggs, or propagules of such species that might survive and subsequently reproduce), whose introduction and/or spread threaten biological diversity and cause economic or environmental harm or harm to human health. AIS may be plant, microbes, insects, animals or fish. Now, this term is much popular in scientific arena of Bangladesh especially in fisheries because of the introduction of several AIS including the wild Piranha.

                 Over the years, Bangladesh has experienced a number of transfers/introductions/translocation of finfish species primarily for aquaculture development. Fifteen species of fishes (Nile tilapia, Mossambique tilapia, GIFT, Common carp, Grass carp, Silver carp, Mirror carp, Bighead carp, Black carp, African Magur, Thai Pangus, Thai Magur, Thai Sarpunti, Piranha and Pirapitinga) have been introduced intentionally or unintentionally for culture purposes, two species (Gourami and Guppy) for pest control, one species (milkfish) for research purpose and at least 46 species for ornamental (aquarium) purposes. Nile tilapia, Mossmbique tilapia, African Magur are native to Africa; Piranha and Pirapitinga are native to Latin America; Common carp, Grass carp, Silver carp, Mirror carp, Bighead carp and Black carp are native to China; Thai Magur, Thai pangus, and Thai Sarpunti are native to Thailand and GIFT (Improved genetic strain of tilapia) is native to Philippines. Tilapias, Chinese carps and Common carp were introduced and now being cultured as they have some unique characteristics like rapid growth in pond, high fecundity, uncomplicated hatchery production of seeds, utilization of natural food, resistant to disease and tolerance to wide range of environmental degradation. Other species like Thai pangus, Thai Magur and Thai Sarpunti were introduced for commercial purposes as they had high market price and customers treat them as replacement for indigenous species. Also, African Magur were introduced for commercial purposes as they can grow quickly in any closed water body with wide range of food (including decomposed fecal matter) but due to its devastating carnivorous nature it has been banned. Now, it is alarming that Piranha and Pirapitinga have been reported to be cultured in different parts of the country as they look alike Chanda fish but none can confirm their ways of introduction. All these AIS have more or less impacts directly or indirectly on biodiversity, ecology and environment which can be discussed as following:

Threats of AIS

Habitat alternation:  Some fishes can directly alter the aquatic habitat like feeding habit of common carp cause pond bank erosion, increased turbidity and elevated nutrient concentrations synergized by substrate disturbance and by excretion. These alterations to physical and chemical conditions have ecological consequences, such as increased phytoplankton density in response to elevated nutrient levels, and reduced aquatic macrophyte growth.  Grass carp feed on aquatic weeds which are in turn, breeding arena of several indigenous fish species. So, reduced plant biomass and cover affect critical reproductive behavior and habitat conditions for invertebrates and fishes, and also fish food resources.

Extinction of biodiversity: Naturally flood and intentionally human are responsible for the introduction of AIS in natural water body. Tiliapias, Common Carp and Chinese carps competes with other indigenous fish species for natural foods (such as planktons, macrophytes and insects), which ultimately make the indigenous species vulnerable. Prolific breeding of tilapias makes natural food unavailable to the local fish species. It has been reported that Mozambique tilapias, which can tolerate brackish water, competes for algae and other resources are displacing mullet and brackish-water shrimp in coastal regions of Bangladesh. African Magur and Piranha directly feed on other local and indigenous species and as a result several species are at the edge of extinction. Pirapitinga is primarily an aquarium fish and feed on prepared aquarium feeds but in absence of that kind of food, they become carnivorous especially in pond ecosystem.

Introduction of diseases/pathogens: In Bangladesh, no in-depth investigation has been carried out to determine the introduction of disease or pathogens by AIS, which may be due to the lack of policies and quarantine facilities, but it is assumed that Argulus sp. has been introduced with the introduction of Chinese carps. It is also suspected that WSSV (White Spot Syndrome Virus) of Shrimp was introduced from the different stock of Shrimp imported from neighboring countries which caused a devastating fall in shrimp market of Bangladesh. If we look at the case of neighboring country, It has been proved that the cestode worm Bothriocephalus gowkonensis was introduced into Sri Lanka with the introduction of Chinese major carps for aquaculture purposes which is already been introduced in Bangladesh.

Socio-economic impacts: These impacts are more significant in Bangladesh as the general fish farmers are not aware of the negative impacts of AIS. They are now more interested to culture AIS species like Tilapia, Silver carp, Common carp, Thai Sarpunti, Piranha and Pirapitinga instead of indigenous fishes as they are getting good market price within a short time with minimum inputs. In this way, the producers and retailers are controlling the customer’s choice and destroying the market of local fishes, which have negative economic consequences. Also, the people are being deprived of nutrition from indigenous fishes like Mola and Dhela.

Genetic impacts: Genetic impacts of AIS fall in of two categories: I) Reduction in “effective population size” by the ecological and other effects of introduction II) Alternation/extinction of gene pools of the species/stocks by cross-breeding/hybridization and backcrossing. It has been reported that the native gene pools of Clarius batrachus (Deshi Magur) have been diluted through the use of hybrid C. batrachus×C. gariepinus for aquaculture. Introgression and hybridization have been reported among Mozambique and Nile tilapia and GIFT. There are also reports on the intentional hybridization among major carps and Chinese carps, which are major threats to the sustainable genetic biodiversity.

Management of AIS

Few countries have developed the comprehensive legal and institutional systems that are capable of responding effectively to AIS. Bangladesh needs to response and make some policies for immediate implementation to manage AIS. The standard procedures for management of AIS include the followings:

Monitoring and inspection: Vigilance and monitoring of known pathways of introduction for inland waters such as the live food fish trade, aquaculture, and aquarium releases, and stocking should be undertaken. Governmental staff should be trained for quarantine, border control, or other relevant facilities to be aware of the larger context and threats to biological diversity, in addition to practical training for aspects like identification and regulation of AIS introduction. The codes of conduct and best management practices, such as the FAO Codes of Conduct for Responsible Fisheries (FAO 1995a) should be followed. For transboundary inland water ecosystems, regional country cooperation is essential for effective invasive alien species management strategies.

Development of policies, rules and regulations pertaining to AIS management: Laws and regulations should be developed to combat the introduction of AIS with concentration on precautionary principles. A watchdog consisting of experts should be formed to revise those laws on the basis of its effectiveness in implementation.

Raising awareness: Involvement of local and indigenous communities and other relevant stakeholders should be promoted at all levels for the identification, prevention and control of invasive alien species in inland water ecosystems. GO and NGO’s should work together to raise awareness against AIS. Importers and exporters should be considered as key target groups for information/education efforts leading to better awareness and understanding of the issues, and their role in prevention and possible solutions.

Controls by different methods: Mechanical, chemical and biological control are used separately or collectively to contain the distribution of the invading species. Mechanical control involves directly removing individuals of the alien invasive species using devices (i.e., netting, angling) or draining of the water body that has become infested. It is highly specific to an invasive alien species, and is often very labor intensive and only applicable for pond system. Chemical control involves the application of pesticides like Cymbush or toxicants like Rotenone. Chemical control is often very effective as a short-term solution for pond ecosystem. Major drawbacks of chemical control are its high cost and non-target impacts on native species and water quality. Biological control involves the intentional use of organisms (e.g., natural predators and pathogens, sterile individuals) to suppress populations of alien invasive species in large waterbody like river. Although, biological control is highly cost‑effective, permanent, and self-sustaining but still there are needs for further research in this field and developing countries like Bangladesh need more manpower and expertise and financial support to implement this control method.

So, now it is the high time to concentrate on the studies of AIS in different perspectives and formulate policies and implement them as soon as possible to save the fisheries of Bangladesh.