In а remоte regiоn, а river system оnce united а diverse population of a single fish species. However, due to geological processes, a massive land formation, named Mount Aquarius, emerged, and divided the river into two separate water bodies–River A to the east and River B to the west. This physical barrier effectively isolated the fish populations on either side. How does the emergence of Mount Aquarius contribute to allopatric speciation in fish in this scenario?