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Fish in troubled waters fight decay

SHANGHAI Water Authority has released more than 16,000 chub and carp fish into Qingcaosha Reservoir in an effort to curb eutrophication and improve water quality, the authority said yesterday.

The reservoir, at the mouth of the Yangtze River, is a major source of tap water for 11 million downtown residents.

The two species of fish will eat the floating planktons in the reservoir and filter the water with their branchia, according to Chengtou Raw Water Co, the reservoir’s operator.

The carp, also known as big-head fish, mainly eat floating microbes, while chubs digest floating plants such as algae as their main food. Together the fish can help to stem eutrophication that leads to excessive plant growth and decay, the company said.

Most of the fish used are medium-sized, weighing about 500 grams, an official with the company said. When they had grown larger, they would be replaced, he added.

Ten thousand chub and carp have also been released into Jinze Reservoir on the upstream section of Huangpu River, which supplies water to some 6.7 million residents in the city’s suburban districts.

The city’s reservoirs are prone to eutrophication because they are at the lowest section of the Yangtze River and Taihu Lake streams. The water from upstream was full of nitrogen and phosphorus materials, which helped the growth of algae and threatened water quality, the official said.

The water authority has launched experiments at the city’s Chenhang Reservoir since 2006 — with Fudan, Tongji, East China Normal and Shanghai Ocean universities — to work out the best fish species and right amount to be released into reservoirs.

A trial operation had been started at the city’s Qingcaosha, Chenhang and Jinze reservoirs, which had proved to be effective, the official added.

The water authority had also planted sequoia trees in and around Qingcaosha Reservoir to help to curb eutrophication.

The trees are expected to reduce the amount of nitrogen and phosphorus materials in the water as well as to contain the growth of algae.


 

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