I have been catching largemouth that have red blisters spots at the base of their fins and tail. What is it?

Welcome to Pond Boss!!

You may get more visibility on your question if you post it in the Questions & Observations category.

If you take a picture of any bass with that condition, that will help too.

These could be as simple as a fish lice infestation. But pics are needed to tell what it actually is.

Thank you for information.

Do the fish look otherwise healthy ?