Answer:
C Allopatric Speciation
Explanation:
Evolution of two populations of same species into two separate species due to geographical isolation is called allopatric speciation.
In the given example, Isthmus of Panama serves as a geographical barrier and do not allow the interbreeding between Atlantic and Pacific fish populations of the same species.
These populations evolve genetic adaptation to make themselves better suited to the prevailing surroundings. Accumulation of genetic variations over generation leads to their reproductive isolation. Now, these two fish populations serve as two separate species as they can not interbreed.