Tail fin torn off

Question
Hi Bob, I'm praying you can help me with my question or point me to someone who can. I consider myself pretty knowledgeable in the freshwater fish area, from experience and endless research. And perhaps I'm just in a panic, but here is my problem. My stepson brought us home a present from the pet store without asking first. A crayfish. After researching crayfish quickly, I figured I would introduce him to my basic tank and see how he does, and remove him if he was too aggressive. He didn't appear to be. BTW, I have platies, black skirt tetra, 2 small shubunkin (waiting to go in my pond when bigger) and 2 small fish that we rescued from our pond and managed to save (not sure if they are koi or a fancy goldfish at this point and they are about 2"+ long now.) This is my problem. It appears as though the crayfish had gotten a hold of my one baby pond fish's tail (big beautiful split goldfish tail)and actually ripped off the bottom part of it. I do not see any open wounds on the baby, it looks just as if it ripped the "flowing" part of the tail off. I'm so upset, and am unsure whether or not the "baby" will be ok or not. He seems none the worse for the wear, is swimming pretty much fine and as I said there are no other visible wounds on him that I can see (I watched him for 1/2 hour carefully examining every part I could). This little fish is very special to us as out of all the fish that were probably hatched and eaten/died in the pond, we saved these 2 little guys from the brink of death, literally. I am just wondering what your opinion is as to what I should do at this point. I thought of the hospital tank with some extra aquarium salt/stress coat/antibiotic, etc., but don't know what would be necessary at this time, if anything. My initial thought was to just let him stay put and watch to see if anything with him changes and then take action. (I tend to put a bit of aquarium salt in my tanks when I first set them up, it's just my preference...also taking in to consideration that tetra's are sensitive to it, so the salt level in the tank now is minimal, but there). All the levels in my water are pristine (I have platy fry in a breeder net right now and a platy ready to give birth in another breeder net). If you could please let me know what you think, I would certainly appreciate it. I'm comfortable in my knowledge with fish and fish care, but when it comes to something like this, I find that I'm second guessing myself because I do NOT want to lose him. I really really appreciate any help you may be able to give me. And I apologize if I have rambled on, I'm just upset. If you need any additional information I would be happy to give it to you. Thanks SO MUCH in advance for your input.

Answer
Hi Bob. You choice is fine. The tail should grow back, and since you said that the baby fish seems to be doing fine with the tail bitten off, there isn't much to worry about. You should be careful with the crayfish, but I expect you already know this, since he could do it again. You could also remove the baby fish and put him a separte tank, if you see he is doing bad, and let him rest. But for now, I believe what you are doing is fine. Hope he gets better!

Alejandra