Files Not Meant For Your Toolbox (or Reef Aquarium): The Genus Pervagor by Henry C. Schultz III

It's a Bird! It's a Plane! No, Istigobius!


For the past couple of months Fish Tales has strayed from its usual focus on typical reef-friendly aquarium fish. One of these unusual subjects was a corallivore, and another of the column's featured species would be happy to eat other vertebrates. Switching gears this month and getting back into a reef-friendly frame of mind, I'd like to introduce a genus of sand or substrate dwelling gobies that generally do not receive much attention from the hobby. Even so, these little fish make perfect additions to mini- and possibly even micro-reef aquariums, not to mention a biotope aquarium which has been gaining popularity lately - mangrove tanks. So don't let these small aquariums sit fishless; add a member of the genus Istigobius!

click here for full size picture
Istigobius species are wonderfully camouflaged and thus are difficult to locate against the sand background. The Rigilius goby, seen here, is a great example of how these fish can blend into their native habitat. Mimicking a sandbed that is similar to the colors of your goby will aid in their transition into captivity and likely allow for ease of viewing. Photo courtesy of Mitsuaki Takata.

Meet the Family

The Gobiidae is the largest family of marine fish with over 2,000 members, and it is still growing. Most Gobiidae are characterized by a few notable attributes. Other than the few gobies that swim above the substrate, most lack a swim bladder and lateral line. Gobies do, however, have sensory ducts surrounding their heads that make up for the lateral line's absence (Smith and Knopf, 1997). Another interesting characteristic is the condition of the ventral fins, which in most gobies are joined together and have small suction cups on the end.

As with so many fish genera, Istigobius was originally described as a subgenus, in this case, of the genus Gobius (Whitley, 1932; Murdy and Hoese, 1985). Even so, many of the current Istigobius species were not originally placed in this subgenus, but instead were spread out among genera such as Acentrogobius, Ctenogobius, and Rhinogobius.

It wasn't until 1979 that Hoese and Winterbottom reviewed the family and subsequently elevated Istigobius to generic status. Despite most often being confused with Acentrogobius, Istigobius was noted to differ by having its nose extend over the top of its lower jaw. Additionally, Istigobius was found to be most closely related to Exyrias, though Exyrias was noted to have "fully scaled cheeks and operculae," while these features are lacking in all Istigobius except I. perspicillatus (Murdy and Hoese, 1985).

The 10 species (see below) of Istigobius all have a few traits in common. Possibly most important to hobbyists is the sexually dimorphic nature of all species. Although the genital papilla is the deciding factor in all species of Gobiidae, this feature is more pronounced in Istigobius. Additionally, several other sexually dimorphic traits are also present such as the longer pelvic fins, darker pigmentation in spots or blotches, and horizontal striping, found on the males.

Gobiidae
Istigobius
campbelli
decoratus
goldmanni
hoesei
hoshinonis
nigroocellatus
ornatus
perspicillatus
rigilius
spence

In the Wild

Istigobius species are found throughout the Indo-Pacific waters, but not all members of the genus are tropical. Two species, Istigobius campbelli and, I. hoshinonis, are restricted in distribution to the temperate seas around Hong Kong and Japan, and another, I. hoesei, has been found only around Sydney, Australia. The remaining species inhabit warmer tropical waters, from the Red Sea to Samoa. Istigobius ornatus is the most abundant species in the genus and can be found from Taiwan to Fiji, down to Queensland, and over to the Red Sea.

Istigobius decoratus is one of the larger members of the genus, reaching nearly five inches. It is seen here amongst the preferred habitat of dark sand and coralline encrusted rubble. When threatened by a predator, it is more likely to remain in the open and stay still (hopefully) blending into the substrate. Photo courtesy of Roberto Sozzani of Scubabob.
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All species of Istigobius are shallow water sand-dwelling fish; that is, they freely roam the sand substrate throughout the day. During their daily activities, however, they are never far from shelter, which may consist of rock, rubble, coral, or mangroves. For such a small fish (reaching a maximum length of five inches), however, it is interesting to note that they do not utilize burrows or crevices for hiding. When burrows in the sand or rock were present while the fish were frightened, in no instance did the fish take refuge in the seemingly safe hideout. Instead, once they flee to a suitable location, they attempt to camouflage themselves by lying still among the sand and rock rubble.

Feeding in the wild will consist of sifting through sand in search of interstitial fauna. By swallowing a mouthful of sand, the sand-dwelling gobies begin the process of eating. Once the fish has a mouthful of sand, it begins to slowly expel the sand out its gills, but only after carefully sifting through it for any small invertebrates. Of course, the fish eats any invertebrates it is able to sift from the sand. Generally, copepods (about 60% of the diet), amphipods, ostracodes, nematodes, and shelled protozoa (foraminiferans) are the main food targets. Naturally, once all the sand has been expelled from the mouth, the fish will repeat the process.

Despite the habitat preference of some species for mangroves and others for coral rubble, all species prefers water less than 20 feet deep. These shallow waters, combined with silty-sand substrate, typically yield water visibility of less than 20 feet. Perhaps this limited visibility is a major reason the fish never move further than several inches from suitable cover.

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The perfect option to add fish life to your mangrove sump is Istigobius ornatus because it is rarely found outside of the shallow, silty mangrove coastal areas. Only keep one per tank, however, as with most members of this genus, the Ornate goby is found as a single individual in the wild. Photo courtesy of Robert A. Patzner, Austria.

In the Home Aquarium

Maintenance of these sand-dwelling gobies is rather simple, provided the aquarist offers them the proper habitat. Small, peaceful aquariums often provide the optimum environment for these gobies' long-term care. One major consideration, however, is the temperature of the aquarium. Maintaining any of the aforementioned temperate sea species will require an aquarium cooler than a typical reef aquarium. Otherwise, a sooner-than-should-be-expected-death will result from the increased water temperature.

The aquarium mates of Istigobius should be restricted to peaceful fish. Other gobies that maintain territories in the middle of the water column would be good choices. These would obviously include Wormfish and cleaner gobies. Gobies that maintain a territory within rocks, corals or burrows are also good choices.

Of course, predatory fish such as lionfish, groupers, or moray eels should be avoided. The gobies will become a quick snack for most any predatory fish. Additionally, predatory invertebrates such as brittle starfish from the genus Ophiarachna should also be avoided. Small gobies such as Istigobius are an easy meal for these aggressive predators. Likewise, anemones such as the Stichodactyla species should be avoided. All too often fish will fall victim to these anemones.

A photo of Istigobius decoratus taken at a depth of 10m, Rodda Reef, Great Barrier Reef,
Queensland, December 1999. The original type specimens collected in 1927 were
lost from Manila as a casualty of World War II.
Photo courtesy of Erik Schloegl.

Compatibility chart for Istigobius:

Fish

Will Co-Exist

May Co-Exist

Will Not Co-Exist

Notes

Angels, Dwarf

 

X
 

A larger aquarium will contribute to greater success.

Angels, Large

 

 
X

Large size and aggressive feeding nature.

Anthias

X
 

 

Provided the aquarium is large enough for Anthias and direct feeding is administered to the goby.

Assessors

X
 

 

Excellent choice.

Basses

 

 
X

May consume Istigobius species.

Batfish

 

 

X

Large size and aggressive feeding habits.

Blennies

 
X

 

Most blennies should do well; larger ones may harass smaller gobies.

Boxfish

 
X

 

The smaller members of the genus are the best options.

Butterflies

X

 
 

Excellent choice.

Cardinals

X
 

 

Excellent choice.

Catfish

 

 
X

May consume Istigobius species.

Comet

X

 

 

Excellent choice.

Cowfish

 
X

 

The smaller members of the genus are the best options.

Damsels

 

X

 

Most damsels can be incredibly abusive to tank mates.

Dottybacks

 

 
X

Most dottybacks will hunt and kill small gobies - Pseudochromis fridmani and P. springeri are possible exceptions.

Dragonets

X

 

 

Excellent choice.

Drums

X
 

 

Excellent choice.

Eels

 

 
X

May consume Istigobius species.

Filefish

X
 

 

Excellent choice.

Frogfish

 
 

X

May consume Istigobius species.

Goatfish

 
 

X

May consume Istigobius species.

Gobies

X
 

 

Excellent choice.

Grammas

X

 

 

Excellent choice, if Gramma is added after goby.

Groupers

 

 

X

May consume Istigobius species.

Hamlets

 

 

X

May consume Istigobius species.

Hawkfish

 

 

X

May consume Istigobius species.

Jawfish

X

 

 

Excellent choice.

Lionfish

 

 
X

May consume Istigobius species.

Parrotfish

 

 
X

Overall size and aggressive swimming nature.

Pineapple Fish

X

 

 

Excellent choice.

Pipefish

X
 

 

Excellent choice.

Puffers

 

 

X

May harass smaller gobies.

Rabbitfish

 

X
 

Should be OK provided the aquarium is large enough for the rabbitfish and enough food reaches the goby.

Sand Perches

 
 

X

Larger individuals may harass or consume Istigobius species.

Scorpionfish

 
 
X

May consume Istigobius species.

Seahorses

X
 

 

Excellent choice.

Snappers

 

 

X

May consume Istigobius species.

Soapfish

 

 

X

May consume Istigobius species.

Soldierfish

 

 

X

May consume Istigobius species.

Spinecheeks

 
X

 

Adult size may be intimidating.

Squirrelfish

 

 

X

May consume Istigobius species.

Surgeonfish

 

X
 

Aggressive feeding and swimming habits will likely require direct feeding of the goby.

Sweetlips

 

 

X

May consume Istigobius species.

Tilefish

X

 
 

Excellent choice.

Toadfish

 
 

X

May consume Istigobius species.

Triggerfish

 

 

X

May consume Istigobius species.

Waspfish

 
 

X

May consume Istigobius species.

Wrasses

 

X

 

Many wrasses are best avoided. The most peaceful ones will be good choices.

Note: While many of the fishes listed are good tank mates for Istigobius species, one should research each fish individually before adding it to the aquarium. Some of the fish listed above are better left in the ocean or for advanced aquarists.

click here for full size picture
Another photo of Istigobius decoratus, this one showing off the highly variable pigmentation possible for the Decorated goby. As opposed to the previous photo which was likely collected closer to the Eastern spectrum of its distribution, this photo was likely taken from waters near Taiwan or the Philippines. Photo courtesy of Mitsuaki Takata.

Another husbandry concern should be the life of your sand bed. Nowadays many hobbyists are concerned about predation upon the sand bed fauna. If this describes you - by all means avoid these fish. As noted earlier, they feed from the sand by sifting it and stripping the vital micro-fauna from it. If you are not concerned about the life within your sand bed, these sand sifters will do an excellent job of overturning the sand and generally keeping it clean. However, you should be concerned about where the sand gets dumped; they are indiscriminate dumpers.

Besides sifting through the sand bed, your new goby will require supplemental feedings of prepared foods. It is likely, especially in smaller aquariums, that the sand bed, by itself, will not provide enough food to sustain the fish. Instead, expect to feed smaller foods designed for a carnivore's diet. Such foods would include mysid shrimps, adult enriched brine shrimp, fish roe, and any of the copious offerings of flake foods.

The behavior of Istigobius allows a wide latitude of potential aquarium sizes. These fish have a tendency not to feel comfortable more than several inches from shelter. As a result, they should do well in aquariums as small as 10 gallons, provided predators are not present. Larger aquariums will be more suitable for those hobbyists wishing to maintain a pair of Istigobius, or those planning on including several tankmates.

Meet the Species

Only two species of Istigobius are regularly available to hobbyists, and not surprisingly, they also have the largest distribution in the genus. I'll start with the most abundant member, Istigobius ornatus, also called the Ornate goby. This goby is rarely found outside of shallow mangrove roots, and in fact is rarely spotted at depths greater than two or three feet. It is best to obtain a single specimen, as these fish do not relate as pairs in the wild. Several individuals can, however, be found spread across a small area; therefore aquariums with an ample sand bed may maintain a small harem of these fish.

The Decorated goby, Istigobius decoratus, differs slightly from other members of this genus. It prefers cleaner waters than do its close cousins. Even so, these fish are rarely found below more than five feet of depth, although collections records do show several individuals taken from as deep as 50 feet. The clean water is probably a direct result of the substrate they prefer - coarse coralline-encrusted rubble.

Another Istigobius species that prefers clear water is I. rigilius, sometimes called by its thoughtfully creative common name, Rigilius goby. It is likely that this and the preceeding species are available in the hobby solely because they make themselves available in clearer water than do their cousins. Unfortunately for hobbyists, this is the only species of Istigobius without sharp sexual color distinctions of the anal or pelvic fins. This species can, however, be sexed by its genital papillae, and on occasion males may develop a series of vertical bars across their abdomen.

Conclusion

In an attempt to find a fish that fits a niche often overlooked by many in this hobby - mini-reef and mangrove tanks - I decided to cover the sand-dwelling species of Istigobius. Their natural instincts and habitats lend a degree of flexibility that is not afforded to us by most ornamental marine fish. As such, these fish place themselves into a small, albeit focused, group of fish that do a fantastic job of filling a niche that the vast majority of fish cannot.



If you have any questions about this article, please visit my author forum on Reef Central.

References:

Baensch, H.A. 1994. Baensch Marine Atlas, Volume 1. Microcosm. Shelburne, VT. 1215 pp.

Jordan, D.S. and J.O. Snyder, 1901. A review of the gobioid fishes of Japan with descriptions of twenty-one new species.. Proc. U.S. Natl. Mus. 24(1244):33-132.

Lieske, E. and R. Myers, 1994 Collins Pocket Guide. Coral reef fishes. Indo-Pacific & Caribbean including the Red Sea. Harper Collins Publishers, 400 pp.

Michael, S.W. 1999. Marine Fishes 500+ Essential-To-Know Aquarium Species. Microcosm. Shelburne, VT. 448 pp.

Murdy, E.O. and D.F. Hoese, 1985. Revision of the gobiid fish genus Istigobius. Indo-Pac. Fish. (4):41 p

Shiobara, Y. and K. Suzuki, 1983. Life history of two gobioids, Istigobius hoshinonis (Tanaka) and I. campbelli (Jordan and Snyder), under natural and rearing conditions.. J. Fac. Mar. Sci. Tech. Tokai Univ. 16:193-205.

Smith, L. L. and Knopf, A. A. 1997. National Audubon Society: Field Guide to Tropical Marine Fishes. New York. p. 615.

Whitely, G.P. 1932. Fishes, in Sci.Rept., Great Barrier Reef Expedition. 1928-1929, 4(9):267-316.




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It's a Bird! It's a Plane! No, Istigobius! by Henry C. Schultz III - Reefkeeping.com