DERA GHAZI KHAN: Though the subsidised project of cage fishing by the government has provided business opportunities to fish farmers, it poses dire threats of eutrophication to the ecosystem, say experts.

Eutrophication is the enrichment of water by nutrient salts that causes structural changes in the ecosystem such as increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce and preclude use.

Experts say the cage fish farming in freshwater bodies or lakes linked with the River Indus poses a threat of eutrophication of the lake as well as creates hazards for endangered marine life, including Indus dolphins.

Saline Water Aqua Culture Research Centre Deputy Director Shaheen told Dawn the government started the project of cage fishing to provide business to fish farmers. He maintained that 5,000 floating cages would be installed in freshwater bodies linked to the River Indus for the cultivation of fish imported from Thailand.

He said more than 100 floating cages were installed in a freshwater lake along the Indus River near Ghazi Ghat while 200 cages were functioning in a lake by the Punjnad Headworks.

Dr Amir Ibrahim is studying the ‘evolutionary ecology’ of the Indus Dolphin at Nánjīng University of Life Sciences in China.

He told Dawn that habitat integrity was the most important element in the long-term conservation of any endangered species.

Cage fish farming in the natural habitat of the Indus Dolphin was not a healthy practice, he added. Uneaten food and fecal material (which contains nutrients) easily settle down and spread with the help of water flow, which later change the natural composition of water and ultimately lead to eutrophication. Once it occurred, it would be almost impossible to control it, he added.

Some fries and fish escape into the natural water. When they would breed with wild fish species, it results in hybrid stock, which may become invasive and dominant species to replace the wild fish species rapidly and resulting loss of natural genetic stock of the wild fish. Any disease from the stock can easily infect the wild fish. All these consequences pose serious threats to the habitat and prey of the endangered Indus River dolphin, he added.

Fisheries Inspector Hussain Mehdi said individual fish could jump into open waters and at least two per cent of unused artificial feed could settle down in depth at the ground level of the lake.

Published in Dawn, December 22nd, 2021