answer:The black spots could be a couple things, are the spots cyst like? If so, then it is a parasite that is found in ponds. If not it could be burn from an ammonia spike in the water. Stress can cause these things to flare up. As far as being kept in a fishbowl, you can keep on in there but you will need to change the water daily or at the very least every other day, if you have a little pump with an air stone that would help aerate the water and put some O2 in there. Fish can change colors due to being stressed out, but what is worse as that with stress fish can easily succumb to diseases. I would definitely keep an eye on him. What kind of fish do you have in the pond? Sounds like you might have some fin nipper type fish mixed in there with the fantail which if you do then it’s going to look real bad for that fantail.