Are these gobies freshwater or brackish?
Please can you advise me as to whether violet gobies are freshwater or brackish fish? I’ve seen them listed as definitely freshwater—in hard water conditions—and also as definitely brackish. I’ve also seen very different adult sizes mentioned so it’s all really confusing. I’m told that they eat mainly algae and vegetable matter and that they can be kept with small fish as they are not predatory. Is this correct? Any advice on keeping them would be fab. I love their prehistoric looks.
NEALE REPLIES: Violet, or dragon gobies, Gobioides spp., are best treated as brackish water fish. In the wild they inhabit mudflats, and for sure, salinity varies and may sometimes be very low. Some Gobioides species certainly inhabit freshwater environments for extended periods, but identifying the fish in front of you isn’t easy, and all the species will thrive in brackish water, so that makes the best default.
In the right tank, these fish are very hardy. They are not at all predatory towards small fish and are, in fact, substrate sifters. Most of their diet is algae and tiny invertebrates that they sift out of the mud using their tiny conical teeth. These fish have absolutely massive mouths allowing them to take in lots of substrate that is then sifted and spat out, presumably with all the tasty morsels retained. It doesn’t really matter what you offer them as they’ll eat all sorts of things, from bloodworms and frozen brine shrimp through to spirulina flake—they are omnivores rather than carnivores, so algae flakes and pellets should be a regular part of their diet.
Some violet goby species get quite big—Gobioides broussonnetii can get to over 50cm long—so you’ll need to feed them generously to keep them in good shape. Even the somewhat smaller Gobioides
peruanus gets to about 25-30cm in length under aquarium conditions.
Despite the fact they are not predatory fish, they’re not something I’d recommend for a typical community set-up. The main reason is that the tank needs specific decor, including a sandy substrate. Given the way they feed, they aren’t going to do well in a tank with a gravel substrate. Fine, smooth, sand is the ideal. Adding a little coral sand will help to buffer the pH but isn’t essential.
They’re also active diggers, and in the wild build large burrows where they hide away when the tide goes out. They’ll also uproot plants without a second thought.
Psychologically, these gobies really need somewhere they can hide out of sight. The classic solution is to use PVC pipes, like those sold for plumbing, cut to an appropriate length. You can bury these in the sand if you don’t want them to be so obvious, and some aquarists assemble lengths of PVC—even including some bends to make the burrow into a U-shape—and then silicone the completed structure to a piece of glass or slate that can be hidden under the sand. Such a construction will stay put, while being easy enough to remove should you need to clean the tank at some point.
Like most gobies, these fish are territorial and antagonistic towards one another, and being slow feeders, aren’t good companions for brackish water catfish that might hog all the food. But they can work well with surface swimmers like mollies, that share the same requirements in terms of water chemistry— and mollies are from the same part of the world, so could be used alongside them in a biotope tank.