Clarias gariepinus is harmful to which organism?

The number of wildlife is continuously decreasing. What is the main reason for this?

The species,which is going to become extinct due to lack of proper care,would be called:

Of the four major causes for the loss of biodiversity (Alien species invasion,habitat loss and fragmentation,over-exploitation,and co-extinctions),which according to you is the major cause for the loss of biodiversity? Give reasons in support.

Match the column $I$ with column $II$:

Column $I$	Column $II$
$(a)$. Thylacine	$(i)$. Russia
$(b)$. Dodo	$(ii)$. Mauritius
$(c)$. Quagga	$(iii)$. Australia
$(d)$. Steller's sea cow	$(iv)$. Africa

Which alien species was introduced into Lake Victoria?