Here's the breakdown:
* Most common green spotted pufferfish (Arothron nigropunctatus): This is the most popular species in the aquarium trade. They don't have a black stomach. Their belly is typically white or a lighter shade of green than their body.
* Other green spotted pufferfish: There are other species of pufferfish that share the common name "green spotted pufferfish", but they are less common in the aquarium trade. Some of these varieties might have darker bellies, even black, but it's not a universal characteristic.
If you are curious about a specific fish, providing more details like its scientific name or a picture would help in identifying its specific features.