Have a large and established marine aquarium on your hands? If you’re looking for an unusual addition, the striking twin-spot goby may be just the fish for you. This sand-sifting goby is a picky eater, but it sure is a fascinating species.
Find out everything you need to know about twin-spot goby care and how to make sure this fish thrives in your aquarium!
|Name (Common, Scientific)||Twin-spot goby, two-spot goby, crab-eyed goby, signal goby, Signigobius biocellatus|
|Minimum tank size||50 gallons|
|Minimum group size||1|
Twin-spot goby description & natural habitat
You don’t have to be a reef connoisseur to figure out where the twin-spot goby (also known as the two-spot goby or crab-eye goby) got its common names. Those eyespots on its dorsal fins really are very striking! In fact, the species’ scientific name, biocellatus, is Latin for “two spots”.
The only member of its genus, Signigobius, the twin-spot goby grows to a maximum size of no more than 4″. It’s not difficult to see why it’s relatively popular in the aquarium trade despite being difficult to keep alive. This really is quite a striking fish! Its body base color is tan, splashed with orange to brown spots all over the body and dorsal fins. It also sports a vertical orange stripe that runs right through the eyes.
The dorsal fins have one eyespot each, with a black outline, yellow “iris” and black “pupil”. The pelvic and anal fins are black with bright blue spots, completely different from the coloration on the rest of the body.
Did you know? Eyespots are also commonly seen in butterflies. They’re designed to be hidden most of the time, but when it feels threatened, the butterfly (or goby, in this case!) can open and flick its wings (or fins), startling predators with the sudden appearance of those big “eyes”. It has been theorized this goby’s eyespots mimic a large crab.
The twin-spot goby was first described in 1977 after it was spotted in Palau, an archipelago in the western Pacific Ocean (although the marine biologists describing it noted that they also found specimens dating all the way back to 1909 in museum collections).
Since then, these gobies have been found to occur all over the western Pacific. They inhabit shallow reefs and lagoons (up to around 100ft in depth), preferably with a sandy or silty substrate that allows them to dig their typical burrows. Many other similar species of gobies share their burrows with pistol shrimp, usually letting the shrimp do all the housework. This one, though, maintains its home itself.
It has been noted the species is usually spotted in pairs.
The IUCN Red List considers Signigobius biocellatus to be a species of Least Concern. Yay! It’s noted to be common in its natural range, and no significant threats to the population have been identified as of yet.
Twin-spot goby aquarium
Although the twin-spot goby isn’t a large fish, we recommend an established aquarium of at least 50 gallons in volume, along with a well-populated refugium and a thick layer of sandy substrate—see the “Diet” section for more information on why. This isn’t a beginner species!
Make sure the aquarium has plenty of hiding places in the form of live rock and the like, though also leave some space for the fish to establish their burrow.
It’s important to choose a tank with a lid. Like many other fish species, gobies like this one are known to jump when startled. They can zoom right out of their tank and onto the floor, which often proves fatal.
Twin-spot goby compatibility
Twin-spot gobies are known to be peaceful fish, at least when there are no other gobies present. They see their own kind as competition and become fiercely territorial if there’s not enough space for everyone to establish their own space! As this species usually occurs in pairs in the wild, we like to keep them like this in our aquariums as well.
This goby species is considered reef-safe. It’s not interested in eating corals and other sessile invertebrates. The only problem you may run into is that it’s prone to spitting sand onto anything that’s too close to the substrate.
Twin-spot goby diet
This goby’s big, wide mouth reveals its diet in the wild: it’s a sand sifter. The species naturally spends its days scooping up mouthfuls of sand, filtering out any small invertebrates, and then expelling the sand from its gills. This is why we mentioned it needs a nice layer (at least 2-3″) of soft substrate in the aquarium.
It’s quite fascinating to see your twin-spot goby diligently scooping and spitting sand in search of tasty morsels, but there is a problem. In most aquariums, there just aren’t enough interstitial (=living between grains of sand) invertebrates present to keep one of these gobies well-fed. Since they don’t really accept food presented in other ways, many end up starving to death.
This preference for small critters found in the substrate is the reason we don’t recommend a nano aquarium for twin-spot gobies like some other sources do. The larger your tank (and the longer it’s been established), the more space for goby food to accumulate!
If your twin-spot takes target-fed mysis shrimp, brine shrimp, or even sinking pellets, that’s great—but you shouldn’t count on it. A refugium that produces plenty of bugs, plus live sand, are the best ways to ensure success.
Tip: If you wouldn’t keep a mandarin goby, definitely don’t keep a twin-spot goby. They’re just as picky, or maybe even worse. We don’t consider this species to be a good beginner fish. If you’re unsure, try something like a yellow watchman goby instead!
Breeding twin spot gobies
Even with a mated twin-spot goby pair and the feeding situation under control, this species doesn’t appear to be very easy to breed in the home aquarium. For starters, telling the difference between a male and female isn’t really possible unless the female is gravid (carrying eggs—she will be much fatter than the male), though if two twin-spots inhabit a burrow together, you can bet on them being a pair.
Here’s how the breeding process works in the wild, according to observations made in the ’70s:
- Gravid females nibble at the male’s body while the pair works on their burrow.
- After spawning, the male is sealed into the burrow for 3-4 days along with the eggs.
- The male is released for burrow maintenance at times, after which he’s sealed back in.
- Eventually, the male leaves the burrow, and it’s sealed up.
- This is where things get vague. Apparently, one or multiple larva(e) continue to develop inside the burrow. It’s not sure where it finds food; maybe there are reserves, maybe it eats its siblings.
- The parents return occasionally to perform further burrow maintenance.
- Eventually, a single surviving juvenile goby emerges from the nest.
- These gobies spawn continuously. It’s been theorized that one pair could have several different burrows with babies in different developmental stages at any given time.
Considering this, it’s not surprising that hobbyists don’t seem to have managed to breed the twin-spot goby yet. It’s a rather complicated process!
Though beautiful, the twin-spot goby is not a suitable fish for beginners. You need a large, established aquarium in order to maintain a pair. They can starve in a small tank!
Want to keep twin-spot gobies or one of the many other beautiful goby species in a nice reef tank, but not sure where to start? That’s what FantaSEA Aquariums is for. Contact us so we can help you design, build and maintain your dream tank—at home, or in the office.
Hoese, D. F., & Allen, G. R. (1977). Signigobius biocellatus, a new genus and species of sand-dwelling coral reef gobiid fish from the western tropical Pacific. Japanese Journal of Ichthyology, 23(4), 199-207.
Hudson, R. C. L. (1977). Preliminary observations on the behaviour of the gobiid fish Signigobius biocellatus Hoese and Allen, with particular reference to its burrowing behaviour. Zeitschrift für Tierpsychologie, 43(2), 214-220.