Dragon gobies (Gobioides broussonnetii) might look formidable, but they are pretty peaceful with other fish species. They eat tiny organisms sifted from the sediment, so they aren’t likely to eat even much smaller fish. They can be territorial among themselves, though, perhaps especially so with like-gender specimens. According to the Fish Lore website, a good combination if you want more than one is a single male and two or three females. So you'll need to know how to tell male dragon gobies from females.
Confirm the species really is Gobioides broussonnetii. Similar species exist that may be confused for and sold as dragon gobies, which need different care and have a slightly different appearance. Compare the fish to those in an online or print aquarium fish reference.
Observe the fishes' behavior closely. Individuals that appear most territorial and aggressive -- chasing each other and fighting -- are likely to be males. If spawning has occurred, the fish guarding the eggs is definitely a male. If this is your tank, transfer his mate to another tank, because she might eat the eggs and newly hatched fry.
Wait until a fish is swimming, which requires patience since dragon gobies are very much bottom dwellers, and examine its genital area -- where waste comes out -- closely. It might be helpful to take a photograph. The only visible physical difference between the genders is in the shape of the genital papilla, a small tube just past the anus. In females, it is rounded. In males, it is longer and pointed.
Items you will need
- Aquarium fish guide
- If you have dragon gobies and they are constantly fighting, whether males or females, you’ll need to separate them or provide a much bigger tank with plenty of hiding places.
- Dragon gobies are long-lived fish that require a huge brackish tank. They are a real commitment -- definitely not a fish for beginners.