About Anguilla bengalensis bengalensis

Anguilla bengalensis bengalensis has been reported from different rivers of Chittagong and Mymensingh district in Bangladesh. But few information is available on this fish to the fish farmers as well as to the fisheries professionals. This article attempts to provide some information on this fish.

Freshwater eels are small- to large-sized fishes (to about 200 cm total length) occurring in most fresh waters of the world except\ principally those of the western side of the American continent and those bordering the South Atlantic. They are rather secretive during the day but actively forage at night, feeding mainly on a wide range of small bottom-dwelling invertebrates. These eels breed in the open ocean and ocean currents move the young larvae (leptocephali) coastward to where the juveniles invade fresh water. Most of the life is subsequently spent in lakes, streams and rivers but as maturity approaches the adults migrate seaward to spawn. Body elongate, but never greatly so, cylindrical in front, and only moderately compressed along the tail. Snout rounded, mouth terminal with the lower jaw projecting slightly, and moderately large, but never extending back much beyond eye; Teeth always small, conical and multi-serial to form narrow to broad bands on jaws and vomer (roof of mouth). Nostrils separated, the anterior one a sort, free tube, the posterior one a simple aperture in front of eye; Branchiostegal rays long but not overlapping ventrally; Gill opening a nearly vertical slit in front of pectoral fin. No spines in fins; dorsal and anal fins continuous around tail; Dorsal fin begins variously between pectoral fin and anus or over anus; pectoral fins always present; no pelvic fins. Minute, oval scales present, embedded in skin. Lateral line system present but not especially prominent, typically as a series of minute, white pores.

Anguilla bengalensis bengalensis is restricted to eastern part of area, from Pakistan to Sumatra): slightly fewer vertebrae 106 to 112, against 107 to 115 in A. bengalensis labiata).
 
More differences between Anguilla bengalensis bengalensis and A. bengalensis labiata are given below:

National Fisheries Policy, 1998 (in part)

10.5 Educational Policies related to fisheries 

 Personnel with appropriate technology and practical knowledge will he required to lead tremendous development opportunities in the fisheries sector. Considering, the present limitations of universities of delivering appropriate practical knowledge and experience based education. a new syllabus will be developed based on field level research and extension experience. Regarding this situation, the following education policies be considered: 

·         In science books, fisheries related theoretical and practical aspects would be incorporated in both primary and secondary education. 

·         In university education, the fisheries syllabus will be rearranged based on appropriate theoretical and practical knowledge.

·         Fisheries education in the universities will be coupled with a mandatory practical work. In this regard, university authorities will take co-operation from the government autonomous It and private bodies. 

·         Expert exchange programmers will be arranged between universities and other agencies related to fisheries programme implementation.

·         In higher studies, national problems will be given priority even performed in foreign countries                        

Fish Identification Tool (Online)

http://www.fishbase.org/Identification/MorphometricsAdvanced/centimeters/index.php

History and Present Status of Fisheries in Bangladesh

The history of fishing in Bengal is more than 4,500 years old (Breazley 1993). For generations, people have harvested fish from ponds, rivers, flooded land, the coast and the deep sea, learning to cooperatively use fishing grounds and market their catch. Fish harvesting and marketing were traditionally considered undignified jobs, so fishers were mainly the low-caste Hindu tribes such as the Majhi, Jaley and Malo. Ponds and lakes continue to feature prominently in the landscape and the lives of rural people. Ponds were traditionally created as borrow pits excavated to supply soil for raising homesteads above flood levels during the wet monsoon. The ponds serve multiple purposes for the rural household, used not only for fish culture but also to supply water for washing, bathing and other household needs. Fish culture in such closed water bodies as ponds and lakes was recorded to have started in 350 BC on the Indian subcontinent (Banglapedia 2008a). In the past, fish farming was extensive and subsistence in nature, stocked with wild fry and fingerlings caught in rivers and cultured without the use of fish feeds. Following the introduction of technology for inducing carp to spawn in the late 1960s and the subsequent development of fishpond management technologies in the 1970s and 1980s, fish farming became widespread and market driven. Culturing various carp and exotic fish species in ponds and lakes became popular all over the country, with the broad participation of all religious and ethnic groups.

Today, about three quarters of Bangladeshis live in rural areas and remain largely dependent on agriculture and natural resources for food and livelihoods. However, some structural changes have occurred in the economy of Bangladesh over the past 3 decades (Hossain and Bose 2000), reducing the prominence of the agriculture sector in favour of the industrial and service sectors, as has been experienced in other developing countries in Asia. The Bangladesh economy has been growing at a respectable rate; average long-term gross domestic product (GDP) growth was 5.7% per year from fiscal year (FY) 1973 to FY2005 (BBS 1993 and2007a, MoF 1990 to 2007 various issues). Although the agricultural GDP has moret han doubled in absolute terms, its share of the national GDP declined dramatically from 54.6% during FY1973-75 to 19.7% during FY2003-05. This reflected the increasing prominence of the industrial and service sectors, which together contributed 45.4% of the GDP during FY1973-75 and 80.2% during FY2003-05. Despite the decline in the share of agriculture in the national GDP, the fisheries sector (including both capture fisheries and aquaculture) has maintained an average contribution of 4-6% to the national GDP (BBS 2007a). Within agriculture, the contribution of fisheries has increased significantly from 7% during FY1973-75 to 15% during FY1993-95 and to 22% during FY2003-05 (Table 2). The fisheries sector experienced 8.9% growth per annum during the decade of 1985 to 1995, the highest growth rate in agriculture, then slowed to 3.7% per annum in the following decade. Several studies have suggested that Bangladesh needs to achieve sustained GDP growth of at least 8-10%, export growth of 20-25% and import reduction of 18-20% to be economically developed before 2025 (Bhattacharya 2002, PC 1995). It appears that the fisheries sector can play a vital role in achieving higher growth in the national economy and exports. Recently, garments and fish have become Bangladesh’s two most important exports.


Source: Country Case Study: Development and Status of Freshwater Aquaculture in Bangladesh. Dey et al. 2008. WFC.

Basic info on Pearl Oyster

Pearl oysters are members of the phylum Mollusca and belong to the class Bivalvia.  Bivalve mollusks are distinguished by having two shells (two valves), a soft body with a small foot, a byssal gland and paired gills.  Pearl oysters are protandric hemaphrodites, which means that most are first male, then female.  The male phase usually occurs during the first 2-3 years of life, with the change to the female phase in later years.  Pearl oysters have been reported to live as long as 25 years.

                                              Fig. Anatomy and life cycle of Pearl oysters.

Pearl oysters reproduce by releasing millions of eggs or sperm into the water column, where fertilization occurs randomly.  In less than 24 hours, the fertilized egg develops into a trocophore larva, a free-swimming organism (Figure).  The larvae remain suspended in the water column for 2-3 weeks before undergoing metamorphosis, changing into an attached juvenile “spat.”  Shortly before metamorphosis, the larva develops an enlarged foot and an eye-spot.  The foot remains after metamorphosis, and the young spat retains the ability to move about for several months even after it attaches itself to a hard substrate.  Pearl oysters can attach and reattach themselves using the byssus. Pearl oysters feed on small algae found in the water column.  The gills in bivalves are large, and tiny hair-like cilia on the gills are used to remove small particles from the water.  Both adults and larvae feed on algae and other small organisms. Clear tropical waters contain limited amounts of algae.  Therefore, a large amount of water must be filtered daily in order for the pearl oyster to obtain sufficient food.  This is the reason that importance is placed on not crowding pearl oysters on the farm and for keeping the shells clean of organisms that compete for food.

Bangladesh Fisheries Sector Overview

Fish plays a major role in meeting the animal protein demand, foreign exchange earning and socioeconomic development of the rural poor by alleviating poverty through employment generation in an agrobased country like Bangladesh. Bangladesh fisheries have three sectors: inland capture, inland culture and marine capture. The inland capture fisheries exploit open water areas of rivers and their tributaries, estuaries, the Sundarban mangrove forest area, permanent wetlands called beel and seasonal flood plains. The inland culture fisheries includes production from closed water bodies such as ponds and ditches, ox-bow lakes, baor, and coastal and inland shrimp and fish farms. The marine fisheries comprise industrial and trawl fisheries and small-scale artisanal fisheries by coastal fisher communities. The total area under inland waterbodies is about 500 000 ha, of which 91 percent is open water and 9 percent closed waterbodies.

There are 265 species of freshwater finfish and 475 marine fish species reported from the country, together with 68 shrimps and prawns, 26 marine and freshwater turtles and tortoises, 24 amphibians, more than 300 molluscs, 2 crocodiles, 1 gavial, about 20 water snakes, about 182 aquatic or wetland birds, and 12 aquatic mammal species. There are 93 species of exotic fishes introduced in the country, of which 18 were introduced for culture fisheries and the rest for aquaria. Two accidental releases of alien species have been recorded so far.

Inland fisheries are the major source of fish to meet national demand. Major carps, exotic carps, catfishes, snakeheads, live fishes, hilsha fishes and small indigenous fishes are the most important fisheries in commerce, and 2005-2006 statistics show that the large and small indigenous species formed 45.43 percent of inland fish produced in the country, followed by major carps (27.59 percent), exotic carps (13.94 percent), large and small shrimps (8.81 percent) and hilsha fishes (4.23 percent). In 2005-2006, the fisheries growth rate of GDP at constant prices was 3.91 percent (based on the year 1995-1996). For 2006-2007, the expected growth rate of GDP was 3.99 percent.

(Source:FAO)

Classification of Piranha and Pirapitinga

Classification of Piranha:

Order: Cypriniformes

Suborder: Characoidei

Family: Serrasalmidae

Subfamily: Serrasalminae

Genus: Pygocentrus

Species: Pygocentrus nattereri

Classification of Pirapitinga:

Class: Actinopterygii Cope 1887 - ray-finned fishes

Order: Characiformes - leporins, piranhas

Family: Characidae

Subfamily: Serrasalminae

Genus: Piaractus (Holmberg, 1887)

Species: Piaractus brachypomus (Cuvier, 1818) 

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.