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Exotic Fishes and Their Positive and Negative Impact on Our

Native Species and EnvironmentIntroduction :

Historically, human actions have been inconsequential on the forces of nature, however, humans are now influencing the processes of the planet. The water bodies of Bangladesh and the world are being invaded by non-native or exotic species. An exotic species is any species intentionally or accidentally transported and released by man into an environment outside its present range. These plant and animal species are considered to be among the most severe agents of habitat alteration and degradation, and they are a major cause of the continuing loss of biological diversity throughout the world. Not all aquatic species that are introduced into new environments are successful; in fact, ecologists predict that most will fail and those that manage to survive will fail to establish reproducing colonies. An ecosystem's resistance to exotic species depends on competition between them and native species for food and habitat. The greater the diversity in an ecosystem, the more competitors an exotic species will encounter, thereby decreasing its chances of becoming established.

Exotic Fish:

Exotic fish is alien species which is not naive and belonging by nature or origin to another part of the world or brought  in from 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  .

Objectives of the Assignment:

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.

How Do These Species Get Introduced? :

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Humans have played an important role in the introduction of non-indigenous organisms into new parts of the world as the rate of dispersal of living organisms has accelerated in proportion with increased human activity around the world. Invading species can be introduced into a new ecosystem by a variety of methods.

Description of Some Exotic Fish Species:The Introduced Exotic Species of the Bangladesh

Exotic fish introduction in Bangladesh have been assessed. 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 .

Figure: Tilapia

(ii) The Chinese Carps :

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They are generally considered to include silver carp, Grass carp, Bighead carp and Black carp.

a) The Silver Carp (Hypophthalmichthys molitrix):

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.

Figure: Silver Carp

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.

Figure: Bighead Carp

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.

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Figure: Grass Carpd) The Black Carp (Mylopharyngodon idella)

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.

Figure: Black Carp

(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.

Figure: Common Carp

(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.

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Figure: Thai Pangas

(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 .

Figure: African Magur

(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.

Figure: Thai Sarputi

(vii) Nilotica (Oreochromis niloticus ): It was brought from Thailand in 1974.

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Figure: Nilotica.

Table-1 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 introduct

ion

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 For culture & to

control aquatic weeds

5 Silver carp

Hypophthalmichthys molitrix

Hongkong 1969 For culture

6 Nilotica Oreochromis nilotica thailand 1974 For culture7 Thai

SarputiPuntius 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 Mylopharyngodon piceus China 1983 For culture

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carp11 African

magurClarias gariepinus Thailand 1990 For culture

12 Thai pangas

Pangasius hypophthalmas

Thailand 1990 For culture

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:

Advantages:

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.

Disadvantage:

i. 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.

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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

Advantages: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.

Disadvantages:

i. Scarcity of grass during dry monthsii. 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

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natural waters of Bangladesh is negligible because of high ambient temperature.

d) Common carp:

Advantages:

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.

Disadvantages:

i. Destroys pond embankments, makes water turbid by turning up mud.ii. Attains maturity early, thereby growth retardediii. Tend to study at high density.iv. Eggs are easily infected by fungus.v. Difficult to harvest with sheet.

e) Silver Carp:

Advantages

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.

Disadvantages

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.

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Impact of Exotic Fish on Environment:

About 12 exotic species have been introduced in Bangladesh. 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.

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.

Recommendations:

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.

Strict quarantine before entry into a new country / region.

Dominantly herbivore species should get preference in selection for culture.

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No pesticide should be allowed in any open water / natural aquatic ecosystems.

Indigenous species should be preferred for stocking and given similar treatments as given to exotics.

The term “trash fish” in polyculture should be dropped. They should be included in the production system and not belittled,

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).

The ratio of stocking surface, column and bottom feeders should be relevant to the natural carrying capacity of these niches.

Utilizing a vacant niche by appropriate exotic species

Increasing exotic fish production in the introduced environment

Filling environment, because of the absence of a similar desirable species in the locality transplantation.

Not accompanying with pest, parasites or diseases such as “Ulcerative syndrome” which might attack native species.

Conclusion:

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

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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.

References:

i. http://en.bdfish.org/2011/01/exotic-fishes-bangladesh/ii. http://en.bdfish.org/category/resource/fish/exotic-fish/iii. http://www.assignmentpoint.com/science/zoology/study-impact-exotic-

fish-culture-bangladesh.htmliv. http://www.banglapedia.org/HT/E_0091.htmv. http://www.amazon.com/Cultured-Ornamental-Exotic-Fishes-

Bangladesh/dp/3843354995vi. http://dictionary.reference.com/browse/exoticvii. http://fish-exotic-website.blogspot.com/2010/09/what-is-fish.html

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viii. http://www.thefreedictionary.com/exoticix. http://www.eoearth.org/view/article/152708/x. http://nas.er.usgs.gov/queries/SpeciesList.aspx?Group=Fishesxi. http://freshaquarium.about.com/od/termsandtables/g/exoticfish.htmxii. http://www.assignmentpoint.com/science/zoology/study-impact-exotic-

fish-culture-bangladesh.html