Choose the correct option for the decline in the population of indigenous catfishes in our rivers due to the introduction of Clarias gariepinus.

The correct option is D Alien species invasion
Earth is considered the treasure of a variety of species. There is a rapid decline in the biological wealth of earth i.e., there is loss of biodiversity on earth. Such loss of biodiversity is primarily because of human activities.

Four major causes of biodiversity loss (The Evil Quartet) are habitat loss and fragmentation, over-exploitation, co-extinction and alien species invasions.

Sometimes the alien species (non-native species) which are introduced into a habitat intentionally, reproduce rapidly, consuming the resources or preying on the native species which leads to a decline of the native species.

One such example is the illegal introduction of the African catfish Clarias gariepinus in our rivers for aquaculture purposes. This African catfish is posing a serious threat to the indigenous catfishes. This can be categorized as alien species invasions.

Hence, option d is correct.

Over-exploitation - Overuse of natural resources by humans leads to over-exploitation of resources. Example: Steller’s sea cow was hunted extensively by the sailors and traders for meat and it eventually became extinct.

Co-extinctions - When certain species become extinct, the plant and animal species associated with it also become extinct. For example, when host fish become extinct then the parasites associated with it also become extinct.

Habitat loss and fragmentation - Increase in human population has led to the loss of habitat and also degradation of the habitat. Large habitats are broken into smaller fragments or smaller patches.