Unfortunately, sir, Doryrhamphus dactyliophorus pipefish cannot be sexed easily or reliably.
For hobbyists who intend to breed the red banded pipefish (which are live bearers like the seahorses), it is customary to order several juveniles and keep them together in the same aquarium until one or more pairs emerge. That’s necessary because it is impossible to accurately sex the pipefish when they’re juveniles, and very difficult to determine gender in even the adult pipefish when the males are not actively breeding and carrying eggs.
If you would like more information about the pipefish, Daniel, including their mating habits and recommendations for breeding and raising them, just send me a brief e-mail to that effect at the following address, and I will be very happy to accommodate you:
Pete Giwojna, Ocean Rider Tech Support