A hole going straight through a fish

Question
Hi,
I have a 15 gallon freshwater tank which is about 9 years old. I have about a total of 10 fish in it; mostly small ones. About 3 weeks ago I cleaned the ecological filter, replaced all of the gravel and switched about 85%-90% of the water with water that had been put in bottles out in the sun for a few weeks (our tap water kills fish) and cleaned the aquarium very well. (I usually do this once a year with no significant problems). I also have a charcoal filter in the tank.
My question is about a problem I have with one of my two harlequin raspboras. Everything was fine until this evening, when I noticed that it was smimming a bit strangely. When I went to look, I saw a hole going straight through both sides of the fish - when the fish swims by I can see straight through it! This happened very suddenly. There is no bleeding, evidence of parasites or a sore - just two holes about the same size on both sides like something speared right through it. I've never seen anything like this before.
I moved the fish into an enclosure because some of my other fish were bothering it; even biting its fins. I very much want to save the fish, do you know what happened and can you help me treat it?

Thanks!
Atara

Answer
Hi Atara,

I've never encountered this type of problem before. I've encountered problems with small holes or indents (which are caused by poor nutrition), and usually only happens with Discus and Cichlids.

However, your problem is entirely different. See if there are any sharp objects in the aquarium that could have caused this. Sometimes, plastic plants and ornaments have sharp edges. You mentioned that there was absolutely no swelling, inflammation, or blood, so an infection is not likely. If none of the other fish are affected, especially the other Rasbora, then it is unlikely that it is a problem with the water.

Fortunately, the damaged tissue will grow back over time. I would say that it should take about 1 to 2 months to fully recover. Adding a slime coat enhancer (this actually comes in the form as your water conditioner, if you're using AquaSafe, AquaPlus, or Stress Coat) will speed up this process. A good water conditioner may be all that you need to make your tap water safe for fish. A water conditioner removes chlorine and chloramine, neutralizes heavy metals, and for some, removes ammonia. This is usually enough to make tap water safe for fish.

When the fish is recovering, make sure that it does not come into contact with the others, because you mentioned that the others were picking on it. Open wounds easily get infected with bacteria, so it may be useful to use an antibacterial fish medication, such as Maracyn or Melafix at half dose to prevent an infection.

Perform 10% water changes daily to help recovery.

Good Luck, and I hope your fish recovers!