The reduction in the number of Indian native fish species in our River resulting from the introduction of Clarias gariepinus falls under which category?

Alien species invasion

The correct answer is Option (4) –Alien species invasion

The decline in the population of Indian native fishes in our river  caused by the introduction of Clarias gariepinus, can be categorized as an "alien species invasion."

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.

Clarias gariepinus, commonly known as the African catfish, is not native to our River and was introduced into the ecosystem either intentionally or accidentally. As an alien species, it is not part of the natural ecological balance in the river, and its introduction can lead to various negative impacts on the native fish species.

The African catfish is known to be a highly invasive species, and when introduced into a new environment, it can outcompete and prey upon native fish species. This disrupts the balance of the ecosystem and can result in a decline in the populations of native fish.