Help: my naso blond has a black spot on his side

[ti-christ]

Hello,

My naso blond has a 2 milimeter black spot on his side and around the black spot the fish skin is more white!

Is it an illness, a parasit or just a bit from another fish?

Note: My naso is still eating as a pig and it does not show any sign of illness.

Here of picture of my naso:

 

[Aqualove182]

Is the black spot smooth? Did he get spiked by another tang?

 

[ti-christ]

I have my tangs for about 4 months and I have never saw any fight between them. In fact, there are always together!

For an unknow reason, the next day the black spot has disappeared and I can not see it !?!?!?

Also, the black was not appearing soft.

Very strange!

Christian