Pollution in Ctg rivers pushes 17 native fish species to extinction

At least 17 species of native fish have been on the verge of extinction in five major rivers of Chattogram over the last one decade because of industrial wastes polluting rivers and sluice gates damaging breeding grounds, finds a study.

The study, conducted from May 2000 to February 2020 on the rivers Karnaphuli, Halda, Sangu, Shikalbaha and Chandkhali in Chattogram, finds eel, alua, river magur, guilsa tengra, bagha aair, corop mohal, nak kata rui, dhela, horned rui, chepchela, kala bata, ghora chela under threat of extinction in the rivers.

The study found 112 fish species and 18 species of shrimp and crabs in these five rivers, Dr Muhammad Ali Azadi, who headed the research, told The Business Standard.

In the Karnaphuli river, 110 species of fish and 18 species of shrimp and crabs have been found.

Besides, 111 species of fish and 18 species of shrimp-crabs have been found in the Sangu river, 74 species of fish and 11 species of shrimp-crabs in the Shikalbaha river, and 72 species of fish and 11 species of shrimp-crabs in the Chandkhali river. In addition, 83 species of fish and 10 species of shrimp-crabs were found in the Halda river.

According to the study, sponsored by the Ministry of Education, 11 species of fish are no longer found in the Karnaphuli river, while 10 species are endangered. In the Sangu river, eight species of fish have vanished in recent years and 12 are endangered. And in the Halda river, six species of fish are in endangered conditions.

Professor Azadi said, "The Shikalbaha and Chandkhali are two important tributaries which connect the Sangu and Halda rivers with the Karnaphuli river. These two connected rivers facilitate the migration of fish. During the breeding season, carp fishes migrate from the Sangu to the Halda to lay eggs."

To protect the Halda, he suggested, seasonal fishing should be banned in the other four rivers as per Bangladesh Gazette 2007 and 2010.

The study found 18 species of shrimp and crab in Chattogram. However, bagda shrimp is in an endangered state in the Karnaphuli and Sangu rivers.

Professor Azadi said different species of foreign fish are also endangered, including nilotica, bighead, silver carp, croaking gourami, etc.

"These fishes, except the croaking gourami, have not been able to breed in a riverine environment. That's why the number of these fishes is very small in the rivers. Besides, the reproductive capacity of foreign fishes in the rivers of Bangladesh is harmful to the environment," he said.

According to Professor Azadi, the International Union for Conservation of Nature (IUCN) in 2000 identified 54 species of fish in the country as being endangered. Again, in 2015, 64 more species were declared endangered.

Notably, the research conducted by Dr Azadi in the five main rivers of Chattogram came up with different results.

"Many of the fishes identified as endangered in the IUCN report can be found in the rivers of Chattogram in sufficient numbers. They labelled these fishes as endangered for a lack of information on their part," said Dr Azadi.

"The survival and number of species of fish depend mainly on the size, length, width, depth, water flow and environment of the river. From that perspective, the fish that are still available in the Karnaphuli and Sangu rivers are not available in the Shikalbaha and Chandkhali rivers because these two rivers are smaller in size, length and depth," he added.

"On the other hand, fish that are not in these rivers, such as ghora chela, gang magur or guilsa tengra, are still found in the Remakri area upstream of the Sangu river," he noted.

Professor Ainun Nishat, a pioneer in water resource management and climate change in Bangladesh, said, "Although the reservoirs outside the five main rivers in Chattogram are known as canals, they are actually rivers. At the end of the Bangla month of Chaitra when it rains accompanied by thunder, many fishes move upstream through these rivers."

"Later, when the weather is favorable, the female fish lays eggs and the male fish their sperm. But these breeding grounds are being damaged due to sluice gates and industrial wastes. As a result, many fishes are facing an existential crisis," he added.

Dr Mohammad Ali Azadi, river researcher and former professor of the Department of Zoology, Chattogram University, and former pro-vice chancellor of International Islamic University Chattogram, headed the research assisted by Mohammad Arshad-ul-Alam, river researcher and associate professor of the Department of Zoology, Chattogram City College.