First National Report Of Pakistan to the Convention on Biological Diversity Ministry of Environment Government of Pakistan Contents

Introduced Cats in Islands of the Arabian Sea52

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Introduced Cats in Islands of the Arabian Sea52

As one sails south of the small Balochi coastal town of Pasni, after about three hours an island with serene blue seas all around becomes visible. The island is locally known as Haptalar and is located some 16 miles from the town of Pasni.

Though the island is not easily accessible and is uninhabited, fishermen from nearby coastal towns like Shah Bandar in Sindh, visit the island seasonally to catch fish, lobsters and oysters. Owing to the negligible human interference and the difficult terrain, a large number of birds used to migrate from the colder regions and spend their winters here. Older fishermen recall that they used to collect a large number of eggs from the islands during the winters. Two rather smaller sandy beaches on the islands also provide a hospitable environment for marine turtles.

Though there are no large mammals on the island, there was a large rodent population that used to destroy the fishing nets of the fishermen. A couple of decades ago, these fishermen brought some cats from the coastal areas to control the rodents. Now these cats have no natural predator on the island and have played havoc with the migratory birds by attacking their nests, destroying eggs and eating up their young ones, hence drastically cutting the number of wintering birds. The cats also dig out pits on the sandy beaches made by turtles and destroy their eggs. The cats, over the years have adapted to the new environment. They have become completely wild, known to even attack the fishermen.

Exotic Fish Species

About 15 fish species have been introduced in Pakistan. Out of these species, swordtails, guppies and goldfish have been imported for ornamental purposes, whereas gambusia was brought for mosquito control. Two species of trout referred to as semi-exotics were introduced for sport fishing. The three Tilapia species were imported to culture in the saline waters of the waterlogged areas. The common carp (Cyprinus carpio) and three Chinese species viz., the silver carp, grass carp and bighead carp were imported by the Punjab Fisheries Department to enhance fish yield per unit area.

With exotic species, it has been observed that these fish have proven effective in achieving the targets for which they were introduced into the freshwater ecosystem of Pakistan. The trout have bred very successfully in the hilly regions. Since the brown trout cannot tolerate higher temperatures, the Punjab Fisheries Department has introduced it into the Murree Hills. Three species of Tilapa (Oreochromis aureus, O. niloticus, and O. mossambicus) are well established in the saline waters of Okara, Bahalwalnagar, Bahawalpur and Rahim Yar Khan. The Tilapia fish is internationally known as the ‘aquatic chicken’ and is relished everywhere in the world. Generally, its size does not grow to more than 200-300 gms, but in Pakistan, this species has been known to grow up to 2-3 kg. This fish has become very popular due to its delicious taste. It is best suitable for culture in saline waters. Tilapia can thrive well, even in half seawater concentrations. The common carp is another fish, which is cosmopolitan, and is found everywhere. This fish has the quality to survive even in adverse aquatic conditions. It can feed on any kind of food present in the water, and breeds naturally in small confined waters. It can breed more than once a year depending upon the temperature of the water. The fish grows to a good size in a year and can survive even in unattended fishponds. The three Chinese carps (Ctenopharyngodon idellus, Hypophthalmichthys molitrix, and Aristichthys nobilis) have surprisingly helped in enhancing the fish yield per unit area. The grass carp that feeds on macro vegetation like buffalo dung has a high growth rate, even more than that in its native China. In Pakistan, this fish lives very amicably with the indigenous culturable species (Catla catla, Labeo rohita and Cirrhina mrigala). Likewise, the silver carp and bighead carp also grow to a very big size, even more than our own culturable species. The average annual weight attained respectively by our culturable species for Catla catla is 2-3 kg, Labeo rohita (not available) and 1.0 to 1.5 kg for Cirrhina mrigala. The grass carp grows to about 2-3 kg, the silver carp is 4-5 kg, and the bighead is 4-5 kg. There has been a significant increase in our yield per unit area because we put all these fish together in our ponds (composite culture, polyculture) where they reside peacefully.

The mosquito fish (Gambusia affinis) has been used as an ornamental fish more than it has been used for the control of mosquitoes. Its population size has significantly reduced, perhaps due to the degradation of its habitat.

Impacts of Exotic Fish

Until now, apart from three exotic species, viz., the common carp, tilapia and silver carp, no detrimental effects have been manifest on our local fish. The common carp is a pond breeder, sometimes breeding twice a year, and has the habit of burrowing at the bottom of and along the dikes of ponds. This makes the water muddy and turbid. Consequently, the gills of all cultured fishes are choked and the process of photosynthesis is retarded. Moreover, its prolific breeding results in a large increase in its population that feeds at the cost of other desired fish. The tilapia, a prolific breeder, competes for space with others’ and its own spawn. Hence, the productivity of the fishpond is reduced.

The third species observed to have affected other indigenous fish is Catla catla. It is known to greatly affect the silver carp. Although Catla catla feeds on aquatic organisms and the silver carp feeds on aquatic plants, the latter is responsible for the reduction of the population of the former. A reason for this may be the silver carp’s active filtering of the maximum quantity of aquatic plants, thus disrupting the food chain for the production of aquatic organisms, as they need to feed on the plants. Table 15.1 gives information on the exotic fish found in Pakistan.

Table 15.1: Exotic Fish in Pakistan53

Common Name

Scientific Name

Brown trout

Salmo trutta fario (Walbaum)

Rainbow trout

Oncorhynchus mykiss (Linnaeus)

Grass carp

Ctenopharyngodon idellus (C. and V.)

Silver carp

Hypophthalmichthys molitrix

Bighead carp

Aristichthys nobilis (C. and V.)

Common carp

Cyprinus carpio Linnaeus


Oreochromis aureus (Steind.)


Oreochromis niloticus (Linnaeus)


Oreochromis mossambicus (Peters)

Gold fish

Carassius auratus (Linnaeus)


Poecilia reticulata (Peters)

Gambusia fish

Gambusia affinis (Baird and Girard)

Black Mollie

Poecilia latipinna (Le Sever)


Xiphophorus helleri (Heckel)


Xiphophorus variatus (Heckel)

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