The marine aquarium opens up an amazing world to the amateur naturalist. Not only does the aquarist have an opportunity to observe a wide array of interesting invertebrates and fishes, they can also witness some of the fascinating symbiotic relationships that occur between these animals on the coral reef. For example, we are all familiar with the sea anemone-anemonefish association. There are many marine aquarists that were drawn into the aquarium hobby as a result of their fascination with this cnidarian-fish association. But there is another invertebrate-fish relationship that I think is even more amazing than this one. It involves a number of goby genera and certain snapping shrimps (family Alpheidae).
The shrimpgoby-snapping shrimp relationship is a mutualistic one – that is, it’s an association where both members benefit. The primary benefit for the goby is that the burrow provides a sanctuary for the otherwise vulnerable fish. In exchange for refuge, the shrimpgobies act as “seeing-eye” fish for their relatively poor-sighted crustacean partners (note: some crustacean experts have suggested that these shrimp actually see quite well, even so their visual acuity is not as good as that of the goby). As the shrimp keeps house or feeds just outside of the burrow, the goby will sit near the burrow’s entrance and “stand guard” (it will also feed and interact with conspecifics at this time as well). The tidy little crustacean moves freely in and out of its refuge, but when it leaves the burrow it keeps in contact with the vigilant goby. It does this by placing one of its antennae on the fish. (This antennal contact is the critical line of communication between the two animals.)
When a predatory fish approaches, the goby will rapidly flick its tail, warning the shrimp of impending danger. If the goby flicks its tail once the shrimp may not respond, but if the goby executes a series of flicks the shrimp it will move quickly back into its burrow. If the predator comes within a critical distance, the goby will also dart (headfirst) into its hiding place. (For a more extensive survey of shrimpgoby biology and behavior go to www.coralrealm.com )
The members of the genus Stonogobiops are some of the most attractive gobies available to marine aquarists. There are six species in the genus, one of which has yet to be formally described – this Stonogobiops sp. is the subject of this article. Only three of the Stonogobiops spp. show-up in aquarium stores with any degree of regularity, and one of these is commonly seen. Two of these species are very similar in color, with alternating white and dark brown to black bands on the body and a yellow head. The three other members of the genus that are not (or rarely) encountered in the marine aquarium trade are: the Dracula shrimpgoby ( Stonogobiops dracula ) from the Maldives, Medon’s shrimpgoby ( Stonogobiops medon ) from the Marquesas Islands, and the fivebanded shrimpgoby ( S. pentafasciata ) that was recently described from Japan.
Unlike the other shrimpgobies, which spend most of their time resting on the substrate, most of the highfin shrimpgobies scull in the water column from 1 to 36 cm (0.4 to 14 in.) over their burrow entrance. Most of these fishes also associate with Randall’s shrimp ( Alpheus randalli ). However, in the Seychelles, S. dracula also lives in association with a shrimp tentatively identified as A. djiboutensis and in Japan, Stonogobiops xanthorhinica will associate with A. bellulus (Polunin and Lubbock 1977, Yangagisawa 1982). In the aquarium, these fishes have also been known to pair-up with other species of commensal snapping shrimp. The Stonogobiops spp. tend to be found at moderate depths 14 to 43 m (45 to 140 feet) on sloping, sandy bottoms at the base of fringing reefs.
The Whiteray Shrimpgoby
One of the most spectacular members of the genus Stonogobiops is the whiteray shrimpgoby ( Stonogobiops sp.). This beautiful fish has a long, white first dorsal spine. It also has bright or rusty orange longitudinal lines on the flanks that are broken into elongate spots on the head and opercula. This beautiful goby attains a maximum length of around 5 cm (2.0 in.). The distribution of this fish is not well known, but it has been reported from southern Japan south to the Great Barrier Reef. It is also collected in Sri Lanka. Even though it is wide ranging and well known to ichthyologists, it has yet to be scientifically described and ascribed a scientific name.
The whiteray shrimpgoby can be found on sand or mixed sand-rubble slopes, where it is most often found at depths in excess of 30 m (98 ft.). It will hover in the water column near its hole, but will also spend a considerable amount of time resting on the bottom near the entrance of its burrow. The whiteray shrimpgoby is very shy and as a result, is very difficult to photograph. The fact that it occurs at greater depths makes getting good photos even a greater challenge. While you can “wait out” many of the shallow water shrimpgobies, there is no time to get the whiteray to habituate to your presence at a depth of 30 m (98 ft.) or more. The only in-situ shots that I have of this fish were taken of a “friendly” individual shown to me off one of the Izu Islands, Japan. (I was able to take two shots before the fish darted into its burrow.)
The whiteray shrimp goby is often observed singly, but is occasionally seen in pairs (like many of the shrimpgobies, pairs may occupy the same burrow during the spawning season). This shrimpgoby is usually found with Randall’s snapping shrimp ( A. randalli ) (some have suggested that what appears to be a color variant of A. randalli may actually be a distinct species). Fortunately for the aquarist, this goby is often available with its shrimp partner, which makes for a remarkable display in the home aquarium.
Keeping the Whiteray Shrimpgoby
It is critical that you carefully acclimate the whiteray shrimpgoby. It is not uncommon for this species to hide for days or even weeks before making an appearance. The first individual I ever kept hid for three weeks. In fact, I thought it was dead. Then one night, just before the tank lights turned off, I saw its head sticking out of a newly formed burrow. The shrimp and goby had found one another and the former had created a small home under live rock on one side of the tank. It took weeks before the fish was brave enough to come out when I was near the aquarium. Because it was so reclusive, the goby had lost a lot of weight. For the next month, I had to make a concerted effort to get food past its hungry tankmates, down to the corner where it lived. In time, the goby became a more aggressive feeder, making more frequent forays into the water column to snatch passing food items.
In contrast, I have also had individuals that were very bold. One such individual “hooked-up” with its shrimp and was making feeding forays the second day after it had been introduced to the tank. But, this individual represents the exception, not the rule for this species.
One way to facilitate whiteray goby acclimation is to avoid keeping it with aggressive tankmates. If the aquarium is home to pugnacious damsels, dottybacks, larger jawfishes, hawkfishes, pygmy angels, aggressive wrasses (e.g., larger Bodianus spp., Pseudocheilinus spp., and Thalassoma spp.), sand perches, and larger, scrappier shrimpgobies (e.g., Cryptocentrus spp.) this fish is less likely to adjust to its new home. That said, once a whiteray has acclimated to a tank, it is possible to introduce fishes that are more bellicose (I would still stay away from overly aggressive species and predatory species that might eat them!). They will often defend their burrow by jaw gaping at an opponent or will simply dart into their refuge if harassed. Although good at aggressive bluffing, these diminutive fishes may not get enough to eat if incessantly hassled by pugnacious tankmates. The Stonogobiops have been known to get evicted from their burrows by larger jawfishes, while substrate-disturbing species, like goatfishes, convict worm gobies, and sleeper gobies may collapse their shrimp partner’s underground architecture.
Of course, the whiteray is potential prey for piscivorous fishes, including large comets ( Calloplesiops spp.), and may fall victim to fish-eating invertebrates, like carpet sea anemones ( Stichodactyla spp.), crabs, and green brittle stars ( Ophiarachna incrassata ). (It is more likely to be preyed upon when it is initially added to the aquarium and has yet to find a crustacean partner.)
This goby is best kept with species that exhibit less interspecific aggression. Good Stonogobiops tankmates include anthias ( Pseudanthias spp. and Serranocirrhitus latus ), assessors ( Assessor spp.), Chromis ( Chromis spp.), more placid demoiselles (e.g., Chrysiptera hemicyanea, C. parasema, and C. springeri ), fairy wrasses ( Cirrhilabrus spp.), flasher wrasses ( Paracheilinus spp.), leopard wrasses ( Macropharyngodon spp.), dragonets, clown gobies ( Gobiodon spp.), Amblygobius gobies, fire gobies ( Nemateleotris spp.), and dart gobies ( Ptereleotris spp.). If housed in a larger tank, it is possible to keep the whiteray shrimpgoby with larger species like butterflyfishes, angelfishes, and surgeonfishes. Fortunately, these reef fishes will typically ignore this goby, but their presence may make an unacclimated Stonogobiops less likely to emerge from its burrow to feed. The only requirement is that the goby is acclimated to a larger tank before these larger tankmates are added.
It is a good idea to keep the whiteray shrimpgoby in a tank that contains small fishes that spend their time feeding in the water column. The presence of these active fishes can help shy fish, like the Stonogobiops spp., “feel” more secure. These tankmates, which are often referred to as “dither fish,” will encourage these gobies to leave their hiding place and investigate their new world. A newly introduced whiteray is also prone to jumping out of an open aquarium when the lights are extinguished or if it’s being bullied. Cover the tank until the fish acclimates and/or provide a night light. Stonogobiops spp. have also been known to bury under fine sand if startled.
The whiteray shrimpgoby, and its congeners, are a wonderful choice for a nano- reef. They do not require much space (I have kept them in tanks as small as 5 gallons) and are easier to observe in a diminutive aquarium. This goby is also more likely to acclimate if kept on its own (i.e., without potentially bothersome fish tankmates). One thing I should point out is that in a tank without dither fish, it may take the Stonogobiops a little longer to overcome its initial shyness. But once it does, it will be quite “happy” not having to compete with more aggressive feeders.
More than one whiteray shrimpgoby can be housed in the same tank. For example, I am currently keeping two of these gobies in a 105 gallon Oceanic aquarium (the footprint is 18 x 48 inches). In this reef aquarium, the snapping shrimp have constructed burrows on opposite ends of the aquarium. (Note: when I added the second goby-shrimp pair, I carefully introduced them to the end of the aquarium, opposite to where the other whiteray had established its burrow). Because these gobies rarely move more than 10 inches from their burrows, I have yet to see them interact. Because of their limited home ranges, I believe that I could get away with slipping another whiteray shrimpgoby into this reef tank.
Fighting in the Stonogobiops spp. consists of mouth-gaping displays, chasing and biting. Sometimes when they bite each other, or other fish species for that matter, they will tenaciously hold their opponent. For example, on one occasion I had to remove a S. nematodes from the jaw of a larger pinkspotted shrimp goby ( Cryptocentrus leptocephalus ). I assume that the larger goby threatened its smaller relative and the latter responded by clamping on with its jaws.
Placing the whiteray shrimpgoby tank in a low traffic area will also facilitate acclimation. For example, it is best not to house a whiteray shrimpgoby in an aquarium in the lobby of a dentist office, where there is a lot of human activity, including kids tapping on the glass. In this venue, the whiteray is likely to hide constantly, and as a result, it will not get enough to eat.
Another Stonogobiops husbandry prerequisite is to feed this fish at least once a day. I feed my whiteray shrimpgobies twice a day. I feed frozen mysid shrimp, Omega One flake food, and a wonderful food called Cyclop-eeze®. The latter is a very nutritious food (e.g., high HUFA and protein content), it remains in suspension longer, and my fish love it! (Ask your retailer to get it by calling 800-521-6258 or by going to www.freezerbar.com – they do not sell direct to hobbyists!). This gives smaller zooplanktivores more time to pick the food particles out of the water column. When you feed them, it is best to place the food in the out flow of a water pump, so that it moves through the water column like their natural prey.
That ends our examination of the fascinating whiteray shrimpgoby. I hope that those of you that have a passive community tank will seek this fish and its shrimp associate out and give it a try! They make fascinating pets. Happy fish watching!