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The actual answer is a.) allopatric speciation
Hope this answer everybody more than the first answer since I am an Expert
The process by which fish evolved changes in their genes to adapt to the new environment and became two different species is allopatric speciation.
What is Allopatric speciation?
Allopatric speciation occurs when two species are separated by geographic isolation. Isolation can occur due to great distance or a physical barrier such as a desert, river or mountain.
With this information, we can conclude that the process by which fish evolved changes in their genes to adapt to the new environment and become two different species is allopatric speciation.
Learn more about allopatric speciation in brainly.com/question/4493180