Apopular species of fish were split by the formation of the isthmus of panama a long time ago. the fish developed changes in their genes to adapt to the new environment and become two different species

A popular species of fish were split by the formation of the isthmus of panama a long time ago. The fish developed changes in their genes to adapt to the new environment and become two different species. This is not because of fish trying to adapt to the new environment but due to the restriction of the gene flow in the fish population. The gene flow maintains the diversity of the different forms of the genes in a population. When it gets restricted the two split populations gradually start to differentiate in terms of the traits they exhibit. At times it can lead to the extinction of one set of population.

answer; i believe the answer is hydraulic action;

what are the awnser choices? i mean, without choices, it is an incompleat