Have a large and established marine aquarium on your hands? If youโre 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 makes a fascinating choice.
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 |
| Temperature | 72-78 ยฐF |
| Salinity | 1.020-1.025 |
| pH | 8.1-8.4 |
| Difficulty level | Intermediate-Hard |
Twin-spot goby description & natural habitat
Description
You donโt 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 speciesโ scientific name, biocellatus, is Latin for โtwo spotsโ.
The only member of its genus, Signigobius, the twin-spot goby grows to a maximum size of no more than 4โณ. Itโs not difficult to see why itโs 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 โirisโ and black โpupilโ. 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. Theyโre 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 โeyesโ. It has been theorized this gobyโs eyespots mimic a large crab.
Natural habitat
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! Itโs 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 isnโt 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 substrateโsee the โDietโ section for more information on why. This isnโt 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.
Itโs 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 thereโs 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.
When it comes to other tankmates, itโs important to choose docile fish like ocellaris clownfish, dartfish, or similar. Peaceful shrimp should also work well and will be left alone by your gobies.
This goby species is considered reef-safe. Itโs not interested in eating corals and other sessile invertebrates. The only problem you may run into is that itโs prone to spitting sand onto anything thatโs too close to the substrate.
Twin-spot goby diet
This gobyโs big, wide mouth reveals its diet in the wild: itโs 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 2-3โณ) of soft substrate in the aquarium.
Itโs 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 arenโt enough interstitial (=living between grains of sand) invertebrates present to keep one of these gobies well-fed. Since they donโt 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 donโt recommend a nano aquarium for twin-spot gobies like some other sources do. The larger your tank (and the longer itโs 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, thatโs greatโbut you shouldnโt count on it. A refugium that produces plenty of bugs, plus live sand, are the best ways to ensure success.
Tip: If you wouldnโt keep a mandarin goby, definitely donโt keep a twin-spot goby. Theyโre just as picky, or maybe even worse. We donโt consider this species to be a good beginner fish. If youโre 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 doesnโt appear to be very easy to breed in the home aquarium. For starters, telling the difference between a male and female isnโt really possible unless the female is gravid (carrying eggsโshe will be much fatter than the male), though if two twin-spots inhabit a burrow together, you can bet on them being a pair.
Hereโs how the breeding process works in the wild, according to observations made in the โ70s:
- Gravid females nibble at the maleโs 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 heโs sealed back in.
- Eventually, the male leaves the burrow, and itโs sealed up.
- This is where things get vague. Apparently, one or multiple larva(e) continue to develop inside the burrow. Itโs 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. Itโs been theorized that one pair could have several different burrows with babies in different developmental stages at any given time.
Considering this, itโs not surprising that hobbyists donโt seem to have managed to breed the twin-spot goby yet. Itโs a rather complicated process!
Conclusion
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? Thatโs what FantaSEA Aquariums is for. Contact us so we can help you design, build and maintain your dream tankโat home, or in the office.
