The reduction in the number of native Indian fish species in our rivers resulting from the introduction of Clarias gariepinus falls under which category?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Alien species invasion
The book lists four main causes of biodiversity loss, called the “Evil Quartet”: habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions. An alien species is one brought into an area from outside. Some of them become invasive and cause the decline or extinction of native species.
Option (1) Coextinction — Incorrect. Co-extinction happens when a species dies out because another species it depends on has become extinct, such as a parasite whose only host dies. The native fishes here are threatened by a newly introduced fish, not by the loss of a partner species.
Option (2) Habitat fragmentation — Incorrect. Habitat fragmentation is the breaking up of a large habitat into small pieces by human activities. The rivers have not been broken up here; a new species has been added.
Option (3) Overexploitation — Incorrect. Over-exploitation means humans harvesting a species too much, like overfishing. The native fishes are not being caught too much; they are being pushed out by the African catfish.
Option (4) Alien species invasion — Correct. The African catfish Clarias gariepinus was brought in illegally for aquaculture. It is an alien species, and it now threatens the native (indigenous) catfishes of our rivers.
NCERT Extract:
Loss of Biodiversity – “… (iii) Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. … The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.”