Gobies and Sleepers: The Low-Down On These Quirky Bottom-Dwellers

Related FAQs: Fresh and Brackish Gobioids, Marine Gobies & their Relatives, Mudskippers,

By Neale Monks

Gobies are probably the only family of fish equally important to marine, brackish, and freshwater aquarists. This reflects their remarkable adaptability -- there are literally thousands of species inhabiting habitats as diverse as mountain streams and coral reefs. The mudskippers, fishes that spend most of their time on land, are gobies in good standing, as is Trimmatom nanus, at a mere 0.4 inches one of the smallest vertebrates known. Some gobies provide a useful healthcare service to larger fishes by eating parasites and dead skin, while others share their homes with other animals, particularly shrimps.

Gobies in the aquarium

Broadly speaking, all gobies want much the same thing. With few exceptions, they are benthic fish that enjoy burrowing, so a tank with a sandy substrate is ideal. Some will also sift the sand looking for food. Most are territorial, and each fish will need a cave to call home, but for the smaller species this may be nothing more than a snail shell with a few square inches around it. Gobies have a reputation for being picky eaters, and live foods are certainly preferred. But most can be weaned onto frozen alternatives such as bloodworms and lobster eggs (these latter are much enjoyed by the small species such as bumblebee gobies).

Perhaps the only serious problem facing any prospective goby-keeper is deciding whether the fish in question needs freshwater or brackish. As a rule of thumb, keeping any unidentified goby in slightly brackish water (SG 1.005) is a good idea, as this will be acceptable to most brackish water and freshwater gobies. Once you know which goby you have, you can then reduce or raise the salinity as required. Of course, if your goby is definitely a freshwater species, and many of them are, then you don't need to keep it in brackish water.

What's in a name?

Bumblebee gobies are the most widely sold gobies, but for all their familiarity, they're among the most difficult of all aquarium fish to identify to species level. For all practical purposes, aquarists should treat them as Brachygobius spp., bearing in mind that fish biologists are only able to identify them by examining dead specimens under a microscope. The bumblebee gobies usually seen in aquarium shops belong to a complex of closely related species including Brachygobius doriae, B. xanthomelas, and B. sabanus. This Brachygobius doriae-group, as it is known, includes species that get to about 1.5 inches in length, which contrasts with the 'dwarf' bumblebee goby group. The dwarf species, including Brachygobius nunus and Brachygobius mekongensis, are less than half the size of the 'big' species. All this sounds simple enough, but the name Brachygobius nunus has quite commonly been applied to 'big' species, and though the dwarf species aren't commonly traded, they do turn up periodically, but are never identified as such. Another name that gets misused is Brachygobius xanthozona. This species is in fact extremely rare in the wild and never traded as an aquarium fish.

Does this plethora of Latin names matter much to the aquarist? In fact it matters a great deal, because within Brachygobius there is a lot of ecological variation. Some species are found in both fresh and brackish waters, but others seem to be confined to freshwater habitats. Brachygobius doriae, for example, is found not only in brackish water but also in acidic waters with virtually no hardness!

So faced with a bunch of unidentifiable bumblebee gobies in a tropical fish store, what's a wise fishkeeper to do? One or other of the Brachygobius doriae-group of species is almost certainly what you'll see, and in theory at least these can be kept in either freshwater or brackish water conditions. Slightly brackish conditions do seem to be the most reliable though, with a specific gravity up to 1.004 being about right. This happy medium seems to suit gobies collected from both freshwater and brackish water habitats.

Errant knights

The knight goby or fan-dancer goby is one of the prettiest of all the gobies commonly traded. Referred to by scientists as Stigmatogobius sadanundio, it is a fairly sizeable species, getting to around 3.5 inches in length and perfectly able to eat small fishes such as guppies and bumblebee gobies. Predatory instincts aside, these are lovely fishes. Both sexes have pearly-white bodies covered in small black spots and a brilliant blue patch on the dorsal fin. Males can be distinguished by their taller dorsal fins.

Unusually for gobies, knight gobies enjoy swimming away from the bottom. This makes them very entertaining pets, and a group of them kept in a reasonably large aquarium will put on a dazzling sight. They are territorial though, so give each fish its own cave. They are also rather nervous when first imported, and will never settle down in a tank lacking suitable hiding places The addition of a few dither fish, such as mollies, will encourage them to settle down quickly.

Knight gobies are basically hardy and adaptable, and have been kept in both hard freshwater and slightly brackish water conditions, though a specific gravity of around 1.002-1.005 seems to work best. These fish are sensitive to dirty water, and good filtration and regular water changes are essential.

The violet weirdo

Ranking number three in the league of easily obtained gobies is the violet goby (or dragon goby). There are multiple species in the hobby, and identifying them is tricky, but the one most frequently encountered in North American stores is Gobioides broussonnetii. Almost always sold as a freshwater fish, this fish will tolerate such conditions for months but for long-term health brackish water with a specific gravity between 1.005-1.010 seems to be essential.

Another misconception is that these fish are predatory. It is true that a violet goby at the brink of starvation will eat a feeder fish, but this is rather like saying that starving humans will eat rats. Kept properly these fish will ignore even livebearer fry, and prefer small invertebrates of various types. They are primarily bottom feeders in the wild, shoveling in mouthfuls of sand and mud and then extracting any tiny worms and crustaceans caught in the process. But they will also extract plankton from the water with a peculiar gulping action, and you can watch this in the aquarium by providing them with small swimming crustaceans such as brine shrimp or daphnia. Besides small animals, algae are also an important part of their diet, and they will scrap algae from rocks using their odd little teeth. If your tank doesn't have enough algae, algae wafers are enjoyed as well.

Predatory sleepers: Butis, Eleotris, and Oxyeleotris spp.

The sleeper gobies tend to be a little bigger and more predacious than other gobies. The flathead gudgeon Butis butis is a typical example and in many ways epitomizes the entire group. Sometimes known as the 'crazy fish' on account of their willingness to perch on objects at most surprising angles, even upside down, most of the time they don't do much but guard their territory. As with most other sleepers, they are somewhat territorial and will chase away conspecifics, but otherwise ignore fish too big to be considered prey. Flathead gudgeons get to about 6 inches in length, and are quite attractive fish, having a mottled brown body and long, rather lizard-like head. They are very hardy animals, and can be kept in a freshwater aquarium for a long time, but they do better in brackish water (SG 1.002-1.010). Apart from smaller fish, they will eat most live foods including worms, insect larvae, and crustaceans. Once settled in, they can be weaned onto frozen substitutes. Given their predatory instincts, these fish are best mixed with reasonably large but otherwise peaceful brackish water fish, such as sailfin mollies, knight gobies, and so on.

A number of Eleotris species are periodically sold as novelty fish, and they can be kept in exactly the same way as the flathead gudgeon. Eleotris fusca seems to be especially common at the moment, most likely because it is rather an attractive fish. Getting to about 8 inches in length, it has a mottled brown body and a thick, golden-yellow band running right along the top surface of the fish from the tip of the snout to the base of the tail. Like many gobies and sleepers, spawning may occur in freshwater but the larvae drift downstream and into the sea. Once the juveniles have reached a certain size, they swim back into estuaries and eventually into freshwater where they mature into adults. This complicated life cycle makes it difficult to breed many gobies and sleepers in captivity.

Even larger than Eleotris fusca is Oxyeleotris marmorata, one of the largest of all the gobies, reaching a whopping two feet in length! Back in the 1980s, these fish were quite commonly traded for a while when giant 'tankbusters' were in vogue, but seemed to vanish from the trade soon afterwards. They're back again, and as big and nasty as ever! On the plus side, adults are spectacular animals, with a strongly marbled pattern of white, brown, and black. They are also very hardy and tolerant of most water conditions, and can be kept in either fresh or brackish water. In their native Southeast Asia, these fish are considered extremely good eating, and are reared in cages held in strongly brackish water (about SG 1.015). They are also quite common in freshwater streams and artificial lakes. Feeding presents no problems, as they will eat practically anything meaty and of appropriate size, though chunky live foods such as river shrimps and earthworms being particularly favored. Juveniles will take bloodworms, brine shrimps, etc. However, on the debt side of the equation it has to be stated that these are very large, very predatory fish that simply grow to large for most aquarists. They are also quite disruptive animals, being both territorial and more than willing to rearrange the aquarium if they don't like the dÅ½cor. Sand and gravel will be shunted about, and plants uprooted in the process. Large rocks and pieces of bogwood are definitely the order of the day. Finally, marbled gobies are somewhat nocturnal so don't expect much activity during the day.

Gentle sleepers: Dormitator and Tateurndina spp.

Though many sleepers are large and predatory, there are others that are much smaller and easier to accommodate in the home aquarium. Dormitator lebretonis is a West African goby that is quite frequently offered for sale as the 'clay goby' or 'mud goby'. Although it certainly will eat substantially smaller fish, its small size -- around 4 inches -- makes this a much easier beast to choose tankmates for. It does equally well in freshwater or slightly brackish water (up to SG 1.005) and generally settles in quickly. An omnivore by nature, to get the best from its subtle but far from unattractive colors it needs a nice mixed diet including brine shrimps and bloodworms but also a certain amount of algae; Spirulina-enriched flake food is ideal. It has a larger cousin, the fat sleeper Dormitator maculatus, which also gets sold from time to time. This North American fish is much larger, getting to about 10 inches or so in captivity. It is primarily a brackish water fish, though it occurs in both fresh and salt waters as well. Both Dormitator are gentle towards fish they cannot eat, but somewhat territorial towards conspecifics. Groups of Dormitator lebretonis can work well, with these fish spending a lot of time in midwater displaying to one another, but don't overcrowd them.

The peacock goby Tateurndina ocellicauda is one of the smallest Eleotrids and certainly among the most colorful. Resembling a killifish in its brilliance, these may be smaller, barely 1.5 inches in length, but their vivid red, yellow, purple, and blue markings give these fish plenty of visual impact. These are strictly freshwater fish, and want water that is around neutral in pH and either slightly soft or moderately hard. Beyond that demand, these fish are fairly easy to care for, though their small size does mean they do best either on their own or with very small and placid tankmates (such as dwarf rasboras). These fish are regularly spawned in captivity, laying their eggs inside a cave and the male guarding the eggs until the fry are free swimming.

The new gobies: Stiphodon and Awaous spp.

Various, usually unidentified, species of Stiphodon have started to become regular features in aquarium shops. Most of these live in streams, and whatever else they need, fast moving, very clean water with lots of oxygen is absolutely essential. A life cycle similar to that of Eleotris fusca seems to be typical, with the adults living in freshwater but the juveniles spending some time in the sea. Typical Stiphodon get to about 2 inches in length. In true goby fashion, these fish rarely leave the substrate, preferring to hop from rock to rock. In the wild at least these fishes feed primarily on algae and the microscopic animals hiding amongst it. In captivity, algae flake is a good substitute, but it is also worth trying to feed small amounts of bring shrimp and bloodworms, though not to excess. Stiphodon species are notoriously difficult to identify, though at least one species, Stiphodon elegans, seems to be fairly consistently traded as the 'neon goby' and can be recognized by its dark green-grey color with brilliant metallic green stripes along each flank.

The genus Awaous has similarly yielded a variety of fresh water and brackish waters species to the hobby in recent years, though the freshwater species Awaous flavus seems to be the most popular. Sold under a variety of names including the 'candy stripe goby' and the 'butterfly goby' this is a very attractive species that reaches about 3-4 inches. Males are a little more brightly colored than the females, but both bear vertical purple bands on the flanks and red markings on the dorsal fin. These are hardy, easy to care for species that become very tame, to the point where they can be easily hand fed. Despite their size, they are completely non-predatory, and feed primarily by sifting sand and extracting small invertebrates. Bloodworms and an especial favorite, but pretty much any small frozen food will be accepted. In a tank with a sandy substrate these fish are very amusing, sometimes completely digging themselves into the sand with only their eyes poking above the surface! The only minus to these lovely fish is a relatively short lifespan: no more than two years. For this reason, don't buy adults but look out for juveniles an inch or so in length.

Gobies are ideal aquarium fishes in many ways. Many are small and colorful, and most are hardy and adaptable. It is heartening to see that in recent years aquarium shops have been increasing the variety of species on offer, a trend this author hopes will continue. In the meantime, if you have a spare tank lying around, why not try something different and go looking for gobies?

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