Do you know the general sexing characteristics?
"Determining the sex of Dwarf Puffers when they're young is very difficult since most of their secondary sexual characteristics do not show up until they reach adulthood. Most of the Dwarf Puffers sold in stores are juveniles, so picking out how many males and females you're getting can be next to impossible. Most owners won't know until their dwarves are grown. When they are old enough, however, it is easy to tell the males from the females: The males have a dark line that runs down their belly (their bellies have more yellow coloring as well). The vertical line on the males darkens with sexual maturity and during spawning. The males also have lines or "wrinkles" behind their eyes that the females do not have. The C. imitator male is identifiable by a "keel" and "comb" created with the ability to erect their dorsal and ventral ridges. Finally, another way to determine the sex of a Dwarf Puffer is to look at its body shape. The female's body will be much rounder than the male's."
1 M. Turgidus - 29 gallon