Sounds just like mine. he must have little teth in there. the bigger he gets the less cute it is for him to nibble my fingers. You wouldnt believe how fat he is, the pics don't show his girth. he eats at least twice as much as the others which is why he is named munchos.
How long have you had your mandarin? My tank is just over a year old and I would love one, but hear they are difficult to keep. What do you feed it? Oh, and gorgeous pictures!