Many reef fish spend a lot of time and energy trying to avoid becoming a meal. Some smaller reef fish rely on quickness and the many hiding places within a coral reef to avoid potential predators. Other fish possess spines to make them less palatable — and in some cases these needlelike structures have associated venom glands. There are also fish that exude a mucus coating that does not taste good and/or is toxic to piscivores. One group of groupers (family Serranidae) renowned for having toxic tendencies is the soapfish. Many of these produce a poisonous slime that they excrete from the skin (known as grammistin) that will produce a white lather, hence the common name “soapfish.” The poisonous slime (grammistin) gives the tribe its name of “Grammistini.”
Although most soapfish do not appear at the top of the list when it comes to bold, bright colors, in terms of behavior they are some of the most engaging fish on the reef. In this article, we will explore their interesting lifestyles and husbandry requirements.
Just what are soapfish anyway? They belong to two tribes (a tribe is a subgroup of a subfamily) in the subfamily Epinephelinae: the Diploprioni and the Grammistini. The two groups include approximately 11 genera and 33 species (three genera and five species in Diploprioni, and eight genera and 28 species in Grammistini). Four of the 11 genera are regularly seen in the aquarium trade, while members of four others are found in stores on rare occasions.
Some of the most unusual soapfish are the members of the genus Diploprion. This genus contains two species that have more laterally compressed, deeper bodies than all of the other soapfish, and they have very long pelvic fins that extend back beyond the front of the anal fin. Unlike most other soapfish, the two Diploprion specis are active during the day, spending much of the daytime hours cruising just above the substrate or hanging under ledges or in caves. When they are hunting for crustaceans and small fish, they adopt a head-down posture as they inspect the sea floor. One of the Diploprion increases its hunting success by swimming alongside larger fish, using them as a mobile blind to sneak up on its prey. The members of this genus are thought to be sexually dimorphic, with males attaining a larger size than females.
Although different in form, the genus Belonoperca is also a member of this tribe. Unlike the Diploprion, the arrowhead soapfish (B. chabanaudi) has an elongate body and a narrow, sharply pointed head. It’s a nocturnal species that spends its days under overhangs and in caves. It shows up in aquarium stores on rare occasions but is well worth seeking out. The other species in the genus, B. pylei, exhibits an amazing color pattern, but occurs in such deep water it is unlikely to be seen in aquarium stores.
Except for two genera, most members in this tribe are not sought-after by aquarists. The only member of the genus Grammistes is the sixline grouper (G. sexlineatus), which is regularly seen in aquarium stores. It is a heavy-bodied species that looks more like the stereotypical grouper than any of the other soapfish.
Two popular species in this tribe belong to the genus Pogonoperca. The most common species in the genus is the leaflip soapfish (P. punctata). This fish is one of the most sought-after soapfish because of its pleasing markings and the leaflike appendage that hangs from the lower jaw. As a juvenile, it is black with large, yellowish-white spots. But as it grows, these break apart, and it becomes light brown overall with small white spots and black saddles. Both the sixline and leaflip spend their days tucked away in crevices and caves, and more actively hunt after dark. Both species have an unusual way of capturing their prey. When closing the distance between themselves and their potential victim, they turn on their side and begin an exaggerated swimming behavior, which may confuse the prey (this has been suggested, but no one is really sure). Both of these species also exhibit a dramatic color transformation. The juveniles exhibit bold but simple color patterns that become more complex as the fish age.
The other members of this tribe are often overlooked because they are less spectacular in appearance and/or are even more reclusive. The genus Pseudogramma (often commonly referred to as “podges”) is comprised of smaller, more secretive species. Only one of these, a western Atlantic species known as the reef bass (P. gregoryi), is seen in the aquarium trade with any regularity.
A few of the Indo-Pacific members of this and more closely related genera (Aporops, Grammistops, Suttonia) do show up in aquarium stores on rare occasions. Although ubiquitous in their natural habitat, these smaller soapfish are rarely seen because of their secretive ways. They live deep in reef crevices, among coral branches or among coral rubble. Some of them are found in more turbulent areas of the outer reef flat and reef crest. They rarely, if ever, leave their hiding places. Instead they prey on crustaceans that share their diurnal haunts.
While little is known about the biology of the Grammistini, at least one member of the tribe, the honeycomb podge (Pseudogramma polyacanthus), is known to be sexually dichromatic and this same species is reported to have large red eggs, which it probably deposits on the substrate. The honeycomb podge is thought to occur in heterosexual pairs, with numerous pairs occupying the same large rubble mound. One member of the genus Suttonia (thought to be a variant of Sutton’s podge, Suttonia suttonia) is more colorful. It is often red with a white skunk stripe on its back and is seen in the aquarium trade on rare occasions. Like the reef bass, this fish is also secretive and spends its entire life deep in reef crevices.
Tribe members of the genus Rypticus are quite different from the other soapfish. Like some in the genus Diploprion, they are laterally compressed, but they are more elongate, with long heads and eyes that can be rotated in their sockets so that they have binocular vision when they look forward. When threatening a rival, they often adopt a head-down posture and spread their gill covers. Rypticus move in a more serpentine manner than their cousins and spend more time sitting on or slinking around the substrate.
Most of these fish live their days wedged in reef crevices, in the interstices between or under rocks, in empty conch shells and among the sessile invertebrates on pier pilings. The young of some Rypticus are common in estuaries and mangrove areas. Some members of this genus have been reported to bury just under the surface of sand or mud, but I have never seen them engage in this behavior in an aquarium.
The Rypticus leave their diurnal shelter sites at dusk and hunt in the same habitat where they spend their more quiescent daytime hours. They typically feed on fish and crustaceans, including small crabs and shrimp, and may ingest several prey items in a single hunting bout. For example, the mottled or bicolor soapfish (R. bicolor) may eat as many as four large shrimp in a single night of hunting.
Like their relatives, the members of this genus have a peculiar way of stalking their prey. When they approach a potential prey item, they will adopt a head-down posture and quiver until within striking range, at which time they will dash forward to grab their victim. Members of this genus are protogynous hermaphrodites — females result from male sex changes.
One downside to soapfish ownership is the potential risk that some species pose to their tankmates because of their toxic body slime. If harassed by a tankmate or the aquarist, or if they are ill, they might secrete copious amounts of grammistin, which could result in the death of the soapfish and any other fish in the tank. Fortunately, this only happens rarely in a home aquarium. The only time I have seen this occur is when a Rypticus species was excessively handled and then placed back into a tank.
If you do notice fish kept with a soapfish breathing heavily or behaving abnormally, remove all of the animals from the tank, and separate the other fish from the soapfish immediately. Do a huge water change (around 80 percent) and use a lot of activated carbon to try and remove the toxin. It may be prudent just to start all over! Unfortunately, if a soapfish is emitting excessive amounts of toxic slime, it is likely to continue to do so if you move it to a new tank, and this will probably lead to its death. But again, this is a very rare problem, so you do not need to worry about this happening.
Also, when capturing a soapfish, use a specimen container, as this is less stressful to the fish. The spines on the gill covers are susceptible to getting tangled in an aquarium net.
Aquarium Needs For Soapfish
Soapfish are durable aquarium inhabitants, but few are highly regarded by hobbyists because of their subdued color patterns and secretive tendencies. This is unfortunate because all soapfish exhibit interesting behavior and will usually acclimate to their keeper in time. The size of tank used to house a soapfish will depend on the species. Some of the smaller members of the group will do fine in aquariums as small as a standard 20 gallon (members of the genus Grammistops, Pseudogramma), while others should be kept in nothing less than 55 to 75 gallons (Belonoperca, Diploprion, Grammistes).
Most members of this group do spend the majority of daylight hours hiding among the aquarium decor, occasionally slinking from one crevice to another. Therefore, it’s important to provide them with plenty of suitable shelter sites. After being in the tank for a while, a soapfish may learn to recognize its keeper as a source of food and become quite tame (this is especially true for members of the genera Grammistes, Pogonoperca and Rypticus).
Some of the soapfish, such as Rypticus, may adopt unusual, even worrisome postures. They have been known to lay on their sides and shove their heads into crevices, with the body and tail sticking straight up in the water column; or they perch on the side of a piece of aquarium decor with the head down and tail up. Although no one is sure why they do this, there is nothing wrong with it — this is just part of the fish’s natural, comedic repertoire.
Members of Pseudogramma and Suttonia are very secretive creatures. In fact, you may only see their heads protruding from a preferred hiding place, or they may make quick appearances in the open to intercept a passing food item. Members of these more secretive genera are best housed in a smaller species aquarium, making it easier to keep track of them and ensure they get enough to eat — this is particularly an issue if these fish are housed with more aggressive eaters, such as other groupers, larger wrasses and triggerfish.
The arrowhead soapfish (Belonoperca chabanaudi) is a secretive species that has some special care requirements. They will not do well if harassed by larger, more aggressive fish tankmates. For the true predatory reef fish aficionado, a species aquarium (perhaps 55 gallons) with a ledge or overhang, some sessile invertebrates that will do well in low to moderate light levels (e.g., star polyps, zoanthids) and an arrowhead soapfish can make a fascinating display. In nature, this species will hang — sometimes upside-down — along the roof of overhangs and caves. Be aware that this is a voracious piscivore that will eat any fish small enough to swallow whole.
Although it may be necessary to induce feeding by offering these fish live food, such as feeder fish and ghost shrimp, in time many species will readily accept bite-size pieces of fresh or frozen seafood, frozen preparations, and frozen Mysis and brine shrimp. That said, the more secretive species (Belonoperca, Grammistops, Pseudogramma, Suttonia) tend to only accept live ghost shrimp (some individuals will also eat livebearers, such as guppies and mollies).
When they feed, some soapfish simply dart out from their lairs, grab the prey item and then dash back to cover. Other species (e.g., Grammistes, Pogonoperca and some Rypticus) slowly move toward their prey and perform unusual swimming motions as they make the final approach. This behavior alone makes it worthwhile to invest the time, space and energy for these fish.
Although most soapfish may behave aggressively toward members of their own species or genus housed in tight quarters with them, they are rarely aggressive toward fish species that are not related. They are, however, very predatory and may surprise you in what they are capable of ingesting. Some of the biggest gluttons in the clan are the sixline soapfish (Grammistes sexlineatus). I have seen them swim around the aquarium for hours with the head or tail of a prey fish they could not swallow sticking out of their mouths. These fish (and others in the group) are able to eat prey items as long as they are and will consume food until their stomach looks as though it may burst.
This ends our survey of these fascinating grouper tribes. Be aware that for humans, the toxin will cause pain only if there is a cut (or orifice) it can enter.
Although not suitable for every marine fish community, these fish can provide the more discerning amateur ichthyologist with hours of viewing pleasure. Happy soapfish watching!