Fish Tales by Henry C. Schultz III

Small-Man's Complex: The Genus Stegastes


Thanks to local aquarium stores nationwide, the first fishes introduced to aquarists, and added to their aquariums, are generally damselfishes. They are sold as fish that are incredibly hardy, usually withstanding all that new hobbyists can give them, and then some. In this regard they probably are the ideal fish for first-time hobbyists. The time will likely come, however, when the aquarist will need to remove these fish from the aquarium in order to keep the peace or be able to add additional, less pugnacious fish. Unfortunately, this often either is not discussed prior to the damsels' introduction, or the aquarium store employees fail to relate and detail the tedious work required to remove the fish. The ensuing attempts to catch and remove these fish will undoubtedly stress the hobbyist, the fish they are trying to catch, and naturally any other inhabitants of the aquarium. Perhaps the most apt present for those less-than-well-liked hobbyists on your Christmas list should be damselfish of the genus Stegastes.

 
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The juvenile color form of Stegastes planifrons might as well be called the wise-man's Rock Beauty Angel because of the poor track record of the Rock Beauty when compared to the survivability of the Threespot Damsel. Adult photo (left) courtesy of John Randall. Juvenile images (above & below) courtesy of Henry C. Schultz III.
 
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Meet the Family

The common name "damselfish" is applied to over 300 marine fish and as a group name, it is accurate enough for hobbyists. Ichthyologists categorize them as belonging in the taxonomic family of marine fish family called the Pomacentridae. This family presently contains 28 genera divided among the four subfamilies. The subfamily Pomacentrinae is where you'll find Stegastes, the feature of this month's column.

Subfamilies of Pomacentridae:
Amphiprioninae
Chrominae
Lepidozyginae
Pomacentrinae

The initial naming of Stegastes occurred when Forster (1801) released his manuscript detailing a new species of fish he chose to call Stegastes lividus. Shortly thereafter, Lacepede (1802) proclaimed Stegastes nigricans as a valid species, but he opted to name it Eupomacentrus, another new generic name for damselfish. Species that are now considered Stegastes were continually added to either genus until Bleeker (1877) revised the genus, declaring Stegastes a junior synonym and a subgenus of Eupomacentrus. Subsequently, Emery and Allen (1980) reinvestigated the genus, and resurrected Stegastes, and placed Eupomacentrus as a synonym of Stegastes. Perhaps interesting to note - the species that were classified under the subgenus of Stegastes were moved to Plectroglyphidodon upon Stegastes elevation to genus.

Considering the outgoing, defensive nature of damselfish, especially those of Pomacentrinae, I find it surprising that new species are still being uncovered. Even so, new additions have been added as recently as 1999 (Stegastes trindadensis), 2000 (S. uenfi) and 2001 (S. robertsoni). Currently, there are 38 species in the genus Stegastes.

Pomacentridae
* Pomacentrinae
Stegastes
acapulcoensis
adustus
albifasciatus
altus
apicalis
arcifrons
aureus
baldwini
beebei
diencaeus
emeryi
fasciolatus
flavilatus
fuscus
gascoynei
imbricatus
insularis
leucorus
leucostictus
limbatus
lividus
nigricans
obreptus
otophorus
partitus
pelicieri
pictus
planifrons
rectifraenum
redemptus
robertsoni
rocasensis
sanctaehelenae
sanctipauli
trindadensis
variabilis
uenfi

In the Wild

Both the Atlantic and the Pacific Oceans have populations of Stegastes, and species from each ocean are common in the aquarium trade. Six species are regularly encountered in the Caribbean; the remaining 22 species are spread across Pacific waters including not only the North and South Pacific, but the Indian Ocean and Red Sea as well. Some species, such as S. fasciolatus and S. albifasciatus, range over a large geographical area incorporating most of the reefs from the east coast of Africa to as far east as Easter Island. However, whereas S. fasciolatus has a considerable expansive latitudinal distribution, stretching from the temperate seas of Japan to the temperate seas of the Great Barrier Reef, the distribution of S. albifasciatus is restricted to the tropical seas not stretching far from the equator. In contrast, S. pelicieri, the species with the smallest geographical distribution, is found only around Mauritius (Allen and Emery, 1985).

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Stegastes pelicieri is noted to remain as a solitary individual throughout its life. Photo courtesy of John Randall.

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The Australian Gregory, Stegastes apicalis, can be found along the entire Great
Barrier Reef and is rarely found deeper than 20 feet. Photo courtesy of John Randall.

Populations of Stegastes species may sometimes be found in small, loosely fit aggregations, but a solitary lifestyle is more likely, or possibly a relationship with a conspecific of the opposite sex. Despite the wide berth given to each pair by the neighboring pair, they often outnumber all other fish species on the reefs of which they inhabit. A couple of factors may play important roles in this. First, they do not actually inhabit a true reef, but instead opt for dying thickets of branching coral, large boulders, man-made structure, and even garbage. Second, they are often found in water no deeper than 20 feet, eliminating all but the juveniles of many other genera of fish from competition for their desired abode. Finally, these species are downright aggressive and are afraid of virtually nothing. They will attack anything that moves into their territory.

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Aggregations of Stegastes bicolor feed cautiously from the water column as a predator looms nearby. Photo courtesy of Henry C. Schultz III.

Allow me to backtrack for a moment. The reader may wonder why these damselfish would take up refuge in the lifeless surroundings of garbage, pier pilings, and dead coral skeletons. After all, surely a nearby reef blooming in astounding colors from its multitude of corals would be the first choice, given the other option of non-living, drably colored, and often algal-infested rubble mounds. Considering that the one doing the choosing is also among the biggest bullies with fins, I can begin to understand why you might be left at bit perplexed. The answer, my friend, lies in the healthy crop of filamentous algae typically found in these locations. What is possibly the single largest problem affecting unhealthy reef aquariums world-wide is completely relished by these nasty little fish. Not only do they desire endless fields of hair algae, but they encourage its growth by farming it. Furthermore, they will defend it to their death. They will rise no more than 10-15 feet at a maximum above their algae garden, and even then only to chase away hostiles (DeLoach, 1999). They will remain with the same patch of algae until another member forcefully ejects them or they die. The total size of the algae mat depends solely upon that particular fish's ability to defend it. The more dominant the individual, the larger its territory. The reason for this nonsense? The algae are the food source of the damsel, and the farming and defending is their way of ensuring they have a meal ready for tomorrow. Algae represent 50% - 90% of Stegastes diet, with the remainder consisting of detritus and benthic invertebrates which are consumed as the fish devour the algae mats.

Typically, the depths they inhabit, as mentioned above, are shallow. Additionally, at each locale the depth zone's range is minimal for all but a few species (Allen and Emery, 1985). As always, a few species stand out as exceptions to the rule. Stegastes altus, S fasciolatus, and S. gascoynei have all been noted to range from the surge zone to depths of nearly 100 feet at the same locale.

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The Japanese Gregory, Stegastes altus, is not widespread enough to make it a regular import for aquarium purposes. The bottom two rays of the pectoral fin are unique for the genus - they are not attached via the membrane but isntead are free-formed. Photo courtesy of John Randall.

Stegastes species use a number of methods to communicate with conspecifics, particularly during spawning. Similar to many marine fish, probably the most frequently encountered correspondence is males displaying or flashing brightly accented colors to females. Take, for example, Stegastes partitus, which is normally 50/50 black and white. When trying to attract a female, the fish becomes predominantly black and only the base of the tail remains white. The tail itself, which is normally white, matches the black of the body's torso. These color highlights are usually associated with a series of mating dances consisting of a series of quick, short bursts in one direction followed by a nearly immediate reversal of direction. Finally, individuals of Stegastes species will produce audible grunts. The grunts are most often produced at the apex of their spawning dance.

Of course, before the male does anything to attract a female he must first get the nest in ideal condition for the female's eggs. The selected site usually is a hard surface such as rock, pier pilings, or dead coral. The male removes all algae and foreign objects, as well as any offending invertebrates such as urchins or starfish, from the area. The tail is used to dust away detritus, while they grasp bulkier items such as algae in their jaws, then remove them by swimming away and dropping them. Mobile invertebrates which often have a good grasp on the rockwork are chased away in similar fashion to how these fish chase away SCUBA divers - persistent nipping of their extremities.

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A clutch of eggs laid by a Stegastes species. Note how they are spread thinly over a large area. Photo courtesy of Henry C. Schultz III.

Once a female accepts the proposition of a particular male, she follows his lead to the nest where she lays a single layer of eggs, which are attached to the rock's surface. The male follows right behind the female and fertilizes the eggs. Females then require several days of rest before spawning again, but males are able to fertilize another clutch of eggs the following morning; thus, he goes right back to work displaying to females. Additionally, it is up to the male to ensure the eggs are tended, although females occasionally may join in on the exercise. Tending the eggs requires removing detritus that has settled on the eggs, providing water movement which encourages proper oxygen levels, and removing eggs that are either unfertilized or that have contracted a bacterial infection. Roughly one week after laying, healthy eggs have hatched and enter the pelagic stage of their life cycle. After spending roughly one month at the bottom of the food chain, the larvae settle into the shallow waters away from established adult feeding and spawning territories. Perhaps in an attempt to avoid aggression from adults, the juveniles look nothing like their adult coloration. Only after they gain size will they transform into their adult coloration and venture into the adult habitat, joining other sexually mature Stegastes species.

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Some species of Stegastes exhibit a different coloration depending on locale. A good example of this is seen in the above two photos of S. fasciolatus, simply called the Pacific Damsel. The image on the left was taken in the Maldives, while the image on the right is a Hawaiian specimen. Photos courtesy of John Randall.

Naturally, a similar group of the communication tools used in spawning is also used as a precursor to attacking intruders. If these warnings are not heeded, an all out assault on the intruder will result. Unafraid of the largest parrotfish or even SCUBA divers, attacks on the skin begin. Most often, the parrotfish and other fish species will move along before outward attacks are launched, but humans are usually not as lucky. Fortunately, their small mouths and Velcro-like teeth are unable to inflict damage beyond an increase in the diver's heartbeat from being startled.

For a short video of a male both providing maintenance and defending his clutch, click the video button:  The video and pop-up window may take a few minutes to load depending on your connection speed. The QuickTime plug-in is necessary to view this video. To download the plug-in click on the image below:


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These photos of Stegastes diencaeus show just how remarkable of a color change occurs as Gregories transform from their juvenile stage to adulthood. Photos courtesy of John Randall.

In the Home Aquarium

Similar to many damsels, the members of Stegastes are characterized as popular reef aquarium fish. To say any particular damselfish, and specifically those of the genus Stegastes, is a hardy aquarium inhabitant would probably be considered an understatement by many hobbyists with experience with these fish. They are resilient to the common mistakes made by beginning aquarists, often to the extent of being able to survive for extended periods of time variations in water parameters that would kill most reef animals. This is obviously why damselfish are suggested to be the first fish into the aquarium by most local marine aquarium stores.

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A preserved specimen of Stegastes emeryi is seen here. Unfortunately, the photo does not show the wonderful blue spots that are prevalent in this species. Photo courtesy of John Randall.

Perhaps the biggest difficulty in keeping these fish is obtaining a balanced mix of tank mates compatible with the damsel. This may as well be the impossible journey, however, because unless the aquarium is of considerable size, the damsel likely will sternly object to sharing its domain with another fish. The best chances of success would be to allow the less aggressive fish to settle within the aquarium long before the addition of the belligerent damsel. Although this will not guarantee success, it will help tip the odds in your favor. Fish to avoid are obviously anything docile such as gobies, small wrasses, and cardinalfish. Some of the better prospective tankmates would be anything considerably larger than the damsel which, at the same time, is unable to swallow the damsel. Possibilities here are puffers, angelfish, and butterflyfish. Naturally, any aggressive fish of equal size will work as well. Such fish would include dottybacks, dwarf angels, and possibly other damselfish. For the full list, please see below.

Compatibility chart for Stegastes species:
Fish
Will Co-Exist
May Co-Exist
Will Not Co-Exist
Notes
Angels, Dwarf
X
 
 
Should co-exist well.
Angels, Large
X
 
 
Should co-exist well.
Anthias
X
 
 
Should co-exist well.
Assessors
 
 
X
Will likely be harassed and/or killed by the Damsel.
Basses
 
X
 
A large tank should house both with minimal squabbling.
Batfish
 
X
 
Damsels may harass Batfish, attacking excess finnage.
Blennies
X
 
 
Should co-exist well.
Boxfishes
 
X
 
Slow and unable to get out of the way, Boxfishes are likely to be excessively harassed.
Butterflies
X
 
 
Should co-exist well.
Cardinals
 
 
X
Will likely be harassed and/or killed by the Damsel.
Catfish
X
 
 
Should co-exist well.
Comet
 
X
 
Comet will likely stay hidden more than usual.
Cowfish
 
 
X
Will likely be harassed and/or killed by the Damsel.
Damsels
 
X
 
Not recommended unless paired individuals are obtained.
Dottybacks
X
 
 
Should co-exist well.
Dragonets
 
X
 
Ignored on most occasions.
Drums
 
 
X
Will likely be harassed and/or killed by the Damsel.
Eels
X
 
 
Should co-exist well.
Filefish
 
X
 
Likely to be harassed, especially Chaetoderma pencilligera.
Frogfish
 
 
X
May attempt to consume Damsel.
Goatfish
 
 
X
Will likely be harassed and/or killed by the Damsel.
Gobies
 
 
X
Varies greatly between species, but the majority will be harassed.
Grammas
 
X
 
Will likely find a quiet corner and never move from it.
Groupers
 
X
 
Will co-exist until they are large enough to swallow the Damselfish.
Hamlets
 
 
X
Will be susceptible to Damselfish attacks.
Hawkfish
X
 
 
Should co-exist well.
Jawfish
 
X
 
Not recommended, but once established a jawfish can hide in its burrow and escape damselfish attacks. May remain mostly hidden.
Lionfish
 
 
X
May attempt to consume Damsel.
Parrotfish
X
 
 
Should co-exist well.
Pineapple Fish
X
 
 
Should co-exist well.
Pipefish
 
 
X
Will likely be harassed and/or killed by the Damsel.
Puffers
 
X
 
Another slow mover that may be the object of frequent, repeated attacks.
Rabbitfish
X
 
 
Should co-exist well.
Sand Perches
 
X
 
Aggressive enough to holds its own, but it may consume smaller damsels.
Scorpionfish
 
 
X
May attempt to consume Damsel.
Seahorses
 
 
X
Will likely be harassed and/or killed by the Damsel.
Snappers
 
 
X
May attempt to consume Damsel.
Soapfishes
 
X
 
Large individuals may attempt to consume Damselfish.
Soldierfish
 
X
 
Lack of defense may be enough to warrant attention from large Damselfish.
Spinecheeks
 
 
X
Will hide continually in the presence of an aggressive fish.
Squirrelfish
 
X
 
Lack of defense may be enough to warrant attention from large Damselfish.
Surgeonfish
X
 
 
Should co-exist well.
Sweetlips
 
 
X
May attempt to consume Damsel.
Tilefish
 
 
X
Tilefish do not mix well with aggressive fish.
Toadfish
 
 
X
May attempt to consume Damsel.
Triggerfish
X
 
 
Should co-exist well except with the most aggressive of Triggers.
Waspfish
X
 
 
Should co-exist well assuming Waspfish is unable to swallow Damsel.
Wrasses
 
X
 
Should co-exist well except for the small docile wrasses.

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

Quite the conundrum is Stegastes insularis. It is very abundant at depths shallower than 15 feet, seemingly making it easy to locate. However, it has only been found at two islands, Christmas Island and Marcus Island - roughly 6,300km apart. Photo courtesy of John Randall.
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Invertebrates are, for the most part, ignored by damsels. Possible exceptions would be small corals placed into their territory that they object to. Although they will not intentionally harm the coral, they will redecorate the aquarium to suit their desires and in doing so may disturb the coral enough to cause stress. Mobile invertebrates, such as snails and crabs, will also be subject to periodic eviction, although this is obviously of less concern.

Food items offered should consist primarily of prepared algae diets, but an occasional mix of carnivorous foods are also appreciated. Algal foods, such as the dried algae commonly called nori at oriental food stores, are some of the popular options, but many frozen, freeze-dried, and pellet options abound. In regard to meaty foods, enriched brine shrimp and mysid shrimp will adequately fill this void. This is especially important for juveniles as a larger portion of their diet consists of copepods due to their lack of an algae farm. Additionally, harvesting the damsel's farmed algal bed would not be a good idea no matter how much you despise filamentous algae. In fact, you may wish to encourage its growth prior to adding the damsel, but allowing it to take over the aquarium would be going too far.

Stegastes aureus, appropriately called the Golden Gregory, is often considered the best looking member of the genus. It is, after all, the only species which is not predominantly brown or black at full adult coloration. Unfortunately, it is not common in the wild, and thus not common in the hobby. Photo courtesy of John Randall.
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The optimum aquarium size for a damsel can vary greatly depending on your interest in mixing other fish species with them. A lone individual will do well in a 40-gallon aquarium provided you do not intend to mix less docile inhabitants with it. Multiple young juveniles will do well in the same aquarium, but as they age and grow they will need to be separated to a minimum of paired individuals. Otherwise, the weakest individuals will be subjected to constant harassment and death will likely soon follow. The aquarium rockwork and aquascaping do not call for anything out of the ordinary. Traditional aquascaping which provides options for an open sandbed and also a place for the fish to retreat and become completely hidden, are key elemental considerations. These fish will spend more than 90% of their daylight hours in the water column, but they still need a place to hide and disappear in the evenings.

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Stegastes obreptus prefers to occupy murky water. It lives so close to shore that a constant wave action stirs the silt from the bottom. The preserved bodies of the juvenile (left) and adult form (right) are pictured here. Photos courtesy of John Randall.

Meet the Species

Possibly the most common Stegastes damselfish is S. planifrons, the Threespot Damsel. You'd be hard pressed not to find a plethora of these damsels on the reefs across the Caribbean. However, their lack of an attractive adult coloration doesn't warrant a high degree of demand within the aquarium trade. The results in an extremely affordable fish that is rather plentiful, but that also lags in sales. Those that do sell are the juveniles, which unlike the adults, have exquisite coloration. Reaching a maximum adult size of five inches, they can be extremely aggressive. As juveniles, they mimic Holocanthus tricolor. The common name is obviously taken from the juvenile color form which sports a single spot on each side just underneath the dorsal fin, and a single spot at the base of the tail.

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As an endemic of the Coral Sea, Stegastes gascoynei has little chance of appearing in the American marine aquarium trade. Photo courtesy of John Randall.

A damselfish with an attractive adult (for Stegastes) is Stegastes variabilis, the Cocoa Damselfish. Juveniles are predominantly yellow and royal blue, but eventually this gives way to the more traditional Stegastes coloring of dark brown or black with accents of blue and yellow. These are among the least aggressive members of the genus. During spawning they are similar to their cousins, but otherwise they make little effort to defend territories. This is because, unlike most members of Stegastes, they do not often setup a true territory, opting instead to patrol open sand areas. Because they are not farming their own algae patch, they also have different feeding requirements. In addition to algae and detritus, tunicates and feather dusters are at risk of being consumed.

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An intermediate coloration of Stegastes variablis shown (left) alongside a juvenile (right). Intermediate photo courtesy of John Randall. Juvenile image courtesy of Henry C. Schultz III.

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Up to 1,000 individuals of Stegastes nigricans have been observed on a single rubble zone flat, loosely occupying the same territory and working in conjuction with one another to drive away any intruding herbivorous fish. The juvenile (above) and adult (below) color forms are pictured here. Photos courtesy of John Randall.
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Another Stegastes not subscribing to the algae farm concept is S. partitus, the Bicolor Damsel. This species forms small aggregations of roughly 10-20 individuals and feeds on plankton in the water column several feet above their hideouts. Their feeding tendencies are more similar to the damselfish known as Chromis than with most other Stegastes, but they remain every bit as fierce to intruders as the typical Stegastes species. In fact, this species will greet intruders in squadron formation; each member of the local hierarchy is quick to join in the defense of their patch reef.

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A rather striking example of the Bicolor Damsel, Stegastes partitus. Photo courtesy of John Randall.

Conclusion

Damselfish fill the niche of a fish meant for the beginning aquarist rather well. They withstand less than ideal water parameters and remain disease resistant, allowing aquarists to learn the hobby without killing large numbers of fish. At the same time, an advanced aquarist can settle in with the knowledge that they will have years of success keeping a fish with an interesting personality. Regardless of which category you represent, do not make the mistake of trying to mix numerous other small, defenseless fish with Stegastes species.

The Blunt-snout Damsel, Stegastes lividus, is seen here in both the juvenile (top) and adult (bottom) forms. Note the change in the facial structure, hence contributing to its common name. Photos courtesy of John Randall.
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If you have any questions about this article, please visit my author forum on Reef Central.

References:

Allen, G.R. and A.R. Emery, 1985. A review of the Pomacentrid fishes of the genus Stegastes from the Indo-Pacific, with descriptions of two new species. Indo-Pac. Fish. (3):31 p.

Allen, G.R.. 1991. Damselfishes of the world. Mergus Publishers, Melle, Germany. 271 p.

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

Burgess, W.E., et al. 1991. Dr. Burgess's Mini-Atlas of Marine Aquarium Fishes MinEdition. T.F.H. Publications. Neptune City. 1023 pp.

DeLoach, N. 1999. Reef Fish Behavior. New World Publications. Jacksonville. 359 pp.

Emery, A. R. and Allen, G. R. 1980. Stegastes; a senior synonym for the damselfish genus Eupomacentrus; osteological and other evidence, with comments on other genera. Rec. West. Aust. Mus. 199-206pp.

Humann, P. 1996. Reef Fish Identification. New World Publications. Jacksonville. 396 pp.

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

Michael, S. W. 1999. Marine Fishes: 500 + Essential-To-Know Aquarium Species. Microcosm. Shelburne. 447 pp.




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Small-Man's Complex: The Genus Stegastes by Henry C. Schultz III - ReefKeeping.com