Aparticular 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 became two different species. what is this process called?

This is speciation. In this process, two distinct species are formed through the intervention of some means such as differing environments or locations. This is done typically as a way of staying evolutionarily competitive in the area in which the species resides. The new species would be the exemplar of that which is best suited to the new conditions.

I've never seen someone post this..

Answer: the dna polymerase checks for errors in dna to prevent replication mistakes.
i hope this !