my puffys belly

Question
i bought my green spotted pufferfish from a fish store, and named him puffy. this was about a week ago.now my little puffy has some black smudges on his belly, but hes swimming fine. should i be worried? wats wrong with puffy? how do i correct this?

Answer
Puffers get black on their bellies when they are unhappy. It might be your water.  Puffers are brackish fish and need salt in their water.  Read more about Brackish tanks here.
http://badmanstropicalfish.com/brackish/brackish.html
If you already have a Brackish tank set up then I recommend you have your water tested.  Puffers like to eat meaty foods (frozen brine shrimp, blood worms and snails) which can lead to a dirtier tank sooner then expected.