India Environment Portal Knowledge for change

About us Contact us
downtoearth-subscribe

Browse by subjects

The war in water

The invasion of exotics is as destructive in water as it is on land. These have rightly been described as "biotic oil spills'. A growing number of uninvited fish, molluscs, plants, plankton and assorted other creatures has turned the lakes into "a veritable soup of exotics.'

An example of how exotics can colonise and destroy great water bodies and the life forms in it is evident from the case of Lake Victoria, which is cradled by Uganda, Kenya and Tanzania. Over the centuries (it is only 12,000 year old) it became home to 500 species of brilliant little fish, most from a single genus. However, they were regarded as "trash fish' because they were too small to be worth catching. Colonial authorities introduced three exotic tilapia fish who would live on the small fish and in turn, feed people.

In what was the greatest single paroxysm of extinction ever recorded, 200 fish species were wiped out. Then followed water hyacinth, a native of the Amazon Basin, possibly brought to Africa as pool ornaments in the 19th century. By 1996 it had choked 90 per cent of the lake's shoreline, choking out the light and sucking out the oxygen.

Related Content