Court Jester Goby

The Court Jester Goby: An Essential Nano Reef Fish?

When it comes to saltwater aquarium (especially those for a reef tank), there are a lot of different attributes to consider. Of course, one of the first things we look for in an “ornamental” fish species is a pleasing or striking appearance. Then, when keeping (or planning on keeping) small, timid fishes or vulnerable invertebrates, we ask, “but is it peaceful and/or reef-safe?” Over time, we certainly might place a high value on additional characteristics such as sourcing (aquacultured or wild-caught), ecologically beneficial behaviors (grazing unwanted algae), and so on.

To be sure, there are rather few fish species that meet all of the above criteria; this small list gets even shorter when the candidate must be (and stay) small enough to fit comfortably within the narrow confines of a so-called nano tank.

Yes, it’s cool that nano aquaria can fit on your office desk. Sure, they’re cute. And they do indeed cost less to build and stock, something important to those on a strict budget. But let’s be honest about one thing: they most definitely are not necessarily easier to operate. Due to their limited volume, water quality can decline rapidly, often leading to algal plagues. Sharply fluctuating conditions, which are much more common in small systems, can stress the hardiest of fish species. A lack of personal space can leave many normally peaceable fish species at each others’ throats. Though it might seem counter-intuitive at first, successfully housing fishes in nano tanks can be a serious challenge!

Given the unique difficulties in maintaining a healthy nano tank, one should put a lot of consideration into any prospective fishes prior to stocking one. In light of how few fish species are even barely suitable for these tiny systems, it might be hard to believe that any can truly thrive in them. But there is one: The court jester goby!


Natural (and captive) history of the Court Jester Goby

Gobies (Family Gobiidae), being so small and typically amenable to aquarium conditions, are generally a must-have for small marine aquaria. Quite a few members of the family are already cultured commercially for use as ornamentals. However, even amongst its closest relatives, the court jester goby is a real stand-out in any size tank. As far as marine aquarists were concerned, everything about this species really changed when it became available to aquarists as an aquacultured species.

The court jester goby (Koumansetta rainfordi), which has also been called Rainford’s goby or the Old Glory goby, is native to countless tropical coral reefs of the western Pacific Ocean from the Philippines to the southern Great Barrier Reef to Fiji. Unlike most members of its family, it is an adapt swimmer and is usually found hovering over the sea bottom. It is most abundant over coral-associated sand or mad flats at depths of 3-30 meters (6.6 to 98.4 feet). While usually solitary, it is somewhat social and can occur in small groups. An omnivore, it targets benthic algae as well as small invertebrates such as copepods.

Perhaps because of its attractive markings—an olive background with bright orange horizontal stripes—it has been regularly targeted by collectors for nearly three decades. The one thing aquarists really liked about the species is its taste for nuisance hair algae. This often became a problem, however, as wild-caught specimens seemed to want little other than hair algae. Indeed, many starved to death in captivity for this reason. This was both surprising and frustrating to many keepers who subsequently wrote the species off as “difficult.”

Two things changed this perception in recent times. The first was the improved availability of live copepods. Having a continuous supply of a nutritious live food—that they’d actually eat—greatly improved the survivability of this species and many like it. At least as important as this was the introduction of aquacultured specimens. Not only are these considerably hardier than wild counterparts (as is usually the case), but they are much less finicky about what they eat. These changes set the stage for the court jester’s fast-increasing popularity as a nano reef fish.


King of the microcosm

Rarely exceeding a length of 2 ½ inches, this little fish can be maintained—for life—in a tank as small as 20 gallons. This of course also has to do a bit with its lack of strong territorial behavior. Captive bred court jester gobies are especially social (just so long as they don’t have to share a small space with their own kind). They are completely reef-safe. And, while they will eat hair algae (something you’ll love, if it starts growing in your tank), these domesticated specimens accept a rather wide variety of food items. They are relatively resistant to common aquarium diseases. Moreover, they “hold” their vivid colors as well as wild specimens and, even better, are produced in a sustainable manner. When searching for the consummate nano reef aquarium fish, it’s pretty hard to look far past the court jester goby!

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