exotic fishes

7/30/2019 Exotic Fishes

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Exotic Fishes

Dr. Shivani Gupta,

PGGCG-11, Chandigarh


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Introduction

-A vast majority of the 300 exotic species introduced into the country are

ornamental fish remaining more or less confined to aquaria. Others have beenintroduced in aquaculture and open water systems with varying degrees of success.

-Three larvicidal fish, i.e.Lebistes reticulatus,Nothobranchus sp. and Gambusiaaffinis, were introduced to contain insect larvae in confined waters.

-Silver carp and the three varieties of common carp were brought into the countrywith the objectives of broadening the species spectrum in aquaculture andincreasing the yields through better utilization of trophic niches.

-In recent years, the bighead carp (Aristichthys nobilis) and O. niloticus have beenreported from the culture systems of eastern India.

- Oreochromis mossambicus, Hypophthalmichthys molitrix, Ctenopharyngodonidella, Cyprinus carpio communis,

-C. carpio specularis and C. carpio nudus have entered the reservoir ecosystemthrough accidental or deliberate stocking. Among them, tilapia, silver carp andcommon carp could be detrimental to the fisheries in various reservoirs in thecountry. Cases of naturalization ofGambusia affinis in reservoirs are rare. InMarkonahalli reservoir, the species has developed as a breeding population and isreported to be affecting the larval stages of commercially important fishes.


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IntroductionTilapia

-The tilapia (O. mossambicus) was first introduced into the pond ecosystem of the

country in 1952 and it was shortly thereafter stocked in the reservoirs of southIndia. By the end of the 1960s, most of the reservoirs in Tamil Nadu and those inthe Palakkad and Trissur districts of Kerala were regularly stocked with tilapia. Theperformance of tilapia in south Indian ponds has been discouraging mainly becauseof early maturity, continuous breeding, overpopulation and dwarfing of the species.According to reports, it matures at an age of 75 days when it is 6 cm in length, andbreeds at monthly intervals under tropical conditions. The warm waters of the

tropical reservoirs in India provide an ideal habitat for tilapia and it has secured aniche in a number of south Indian reservoirs. Concerns regarding its stunted growthhave been allayed as the average size of tilapia did not decline as much as it did inponds.


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Introduction

-O. mossambicus was introduced in India at a time when inland fisheries contributednegligibly to the total fish production in the country and at the outset of theecosystem management. Today, a number of indigenous species are available forstocking in order to broaden the species spectrum, bridge the gaps in nicheutilization and increase the yield. With the exception of very few reservoirs, tilapia-dominated fishery invariably leads to low yields. In many reservoirs such asKrishnagiri and Vaigai, production has been erratic because of the unpredictablebehaviour of tilapia owing to competition with other fish. Fishery managers of Indiaare striving to change the dominant position of tilapia wherever it occurs. Given thepresent situation, tilapia is not among the species preferred for stocking in Indianreservoirs.

-O. niloticus has not yet been introduced to the reservoir ecosystem in India. Confinedto the estuarine and freshwater wetlands of eastern India, the species has registeredan impressive growth of 250 g in 6 months. Since this species is not reported tohave problems of stunted growth and prolific breeding, it will probably play a morepositive role than that ofO. mossambicus in Indian reservoirs.


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IntroductionSilver carp

-Silver carp (Hypophthalmichthys molitrix) was introduced in India in 1959 and, unliketilapia, did not stray into many reservoirs. However, silver carp has attracted moreattention from ecologists and fishery managers, generating a more animated debate.The significance of silver carp in reservoirs is mainly because of:

1) its reported ability to utilize Microcystis;

2) its impressive growth rate; and

3) its propensity to affect indigenous species, especially Catla catla.


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IntroductionSilver Carp

-The idea of stocking silver carp in reservoirs was abandoned following experimentalintroductions in the Kulgarhi (Madhya Pradesh) and Getalsud (Bihar) reservoirs.The most impressive reported performance of silver carp was in the Gobindsagarreservoir, where, following an accidental introduction, the species formed abreeding population and brought about a phenomenal increase in fish yields. Silvercarp was instrumental in incrementing the fish production from the reservoir from160t in 1970-71 to 964t in 1992-93. It is significant to note that despite its entry intoa number of Indian reservoirs, by accident or otherwise, silver carp failed tobecome naturalized anywhere except Gobindsagar. The reservoir, with its temperateclimate, is closer to the original habitat of the species and has a distinctly cold waterhypolimnion owing to the discharge from Beas. In this reservoir, silver carp seemsto have found a congenial habitat for growth and propagation. Although theintroduction of silver carp was never cleared by the Committee of Experts

constituted by the Government of India, the fish is being stocked in a number ofreservoirs in the country, but so far has not had the same success in any otherreservoir as it did in Gobindsagar. Therefore, fears regarding the threat of catlaextinction in the Gangetic and peninsular areas of India because of silver carp arepossibly groundless


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IntroductionCommon carp

-The three varieties of the Prussian strain of common carp, i.e. the scale carp(Cyprinus carpio communis), the mirror carp (C. carpio specularis) and the

leather carp (C. carpio nudus), were introduced in India in 1939. During

the 1950s they were stocked in several high altitude ponds and lakes. In

1957 the Chinese (Bangkok) strain of the common carp was brought into

the country, primarily for aquacultural purposes, because of its warm water

adaptability, easy breeding, omnivorous feeding habits, good growth andhardy nature. Like tilapia, common carp soon found its way to all types of

reservoirs in the country..


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Introduction

Other exotic speciesThe exotic carp, being considered for introduction in the country are the bighead

carp (A. nobilis), already introduced unofficially,

the mud carp (Cirrhinus molitorella),

and the snail carp (Mylopharyngodon piceus).

-All of them infringe on the food niche of the economic carp species of India

and the alien species were likely to cause the extinction of their nativecounterparts.

Mud Carp


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Introduction

Other exotic species

Big Head Carp

Snail Carp

exotic fishes

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