I've just brought home a new betta and i've noticed his tail seems damaged. I'm not sure if it's been injured or if he has fin rot (have never dealt with fin rot before). Any help would be really appreciated.
I would be inclined to say that's some fin nipping from shipping stress. It looks tattered as opposed to melted or torn and the surrounding area seems pretty unaffected.
When I had some shipped I left them in a small quarantine tank for about a week with only a heater and some IAL for cover (tannins are also a benefit). No lights or filter but do keep up on removing waste and extra food daily. Change half the water at least every other day matching the temp. Monitor the fins for any changes. Also would be a good idea to try and find some frozen brine shrimp or blackworms. They are high in nutrition and can help the fish regain energy and the nutrients to heal.
Beautiful fins though. Completely agree with Sinned on the nipping. Take good care of the betta with some Indian almond leaves or red Bush/rooibos tea and maybe a low dose aquarium salt, and clean water! You’ll likely see those grow back.