^ What type of spotted puffers are you talking about exactly??? since there are a few species that have spots which range from completely freshwater to full marine... maybe if you could post a pic it would help?
As for feeding, basically you can't go wrong with a mix of the following: Defrosted Frozen Shrimp, Mussels, Scallops, (talipa fillets if its a piscivore), snails for wearing down teeth, blood worms etc...