Hard to categorize, the Sixline Soapfish is both peaceful and hardy, as well as aggressive and suggested for experts only!

The Sixline Soapfish is brown, deep bodied fish with 8 or more closely spaced, horizontal white lines that are broken up into dashes.  The head area has white spots and can have a few “dashes” as well.  Juveniles start out black with whitish yellow spots, which, as the fish grows, eventually turn to 3 whitish yellow stripes, then 6 white stripes and eventually on to the lined dash pattern of the adult.  The fins are all rounded except the first part of the double dorsal fin.  As juveniles the fins are clearish and adults have clearish brown fins.  This ever changing fish are considered expert only and can grow to 11.7” (30 cm).  

The Sixline Soapfish is the only fish in the Grammistes genus, and the toxin found in their body slime which they can emit at will is called Grammistin.  Although listed as a grouper quite often, this fish is different due to, not only it’s smaller size, but that their skin can emit this toxin.  Juveniles up to .07” look similar to a noxious slug from the Phyllidia genus.  This coloring is more visible in the darker parts of the reef which the fish is commonly found in during the day.  That being said, yes, the fish is nocturnal and hunt at night.  When hunting, they pose with their nose pointed down and upon seeing prey, they turn their body’s sideways and swim in an exaggerated pattern, possibly to confuse it.   As the prey is texting it’s friends to come see the freak who just moved into the area, who is swimming all weird-like, the Sixline Saopfish instantly snatches up his dinner!  Even when feeding in captivity, the Sixline Soapfish will slowly approach it’s chunk of food, and snatch it up in the wink of an eye, much to the amazement of it’s owner.  This fish will also emit a poison that makes them taste very bitter to their attackers.  

This fish is marked as “expert only” due to their ability to take out an entire tank if they die or are frightened by another fish, become ill, or if the aquarist unknowingly freaks it out.  Though this is not a common occurrence, it only needs to happen once!  Sixline Soapfish, once established, are very hardy.  Leaving juveniles alone when first introduced is a good way to help them adjust.  Provide them with many places to hide and do not house them with aggressive fish that may try to attack them.  As they grow they will become more tame.  Be sure to only capture your Sixline Soapfish with a container, not a net.  They will become more stressed when captured with a net, since nets can snag the spines by their jaw and ears.  If the other fish in the tank are suddenly breathing heavily, quickly remove them to another tank, since your Sixline Soapfish may have emitted the grammistin toxin.  This toxin is also a skin irritant, so never handle your fish with bare hands or pet or kiss their body!   

Soapfish get along with all other fish, except other soapfish and very aggressive fish.  Only one per tank.  They will eat any fish up to as long as they are, to the point of not even being able to swallow the fish completely!   It is quite interesting to see your Sixline Soapfish swimming around the tank with the head or tail of their prey sticking out!  Eventually, as it is digested, the prey will disappear.  Hopefully, it was not an expensive dinner!  Other fish should not be overly aggressive like the aggressive Clown Triggerfish, since it may “trigger” the “soap up” mechanism.  See what I did there?  Triggers that trigger toxins?  Okay, moving one!  So, say you want a mandarin or a toby?  They emit toxin and should be safe, right?  Wrong!  Sixline Soapfish can eat tobies and other fish that are noxious too!  Add your soapfish to the tank as the first resident and allow your Sixline Soapfish to adjust fully before adding other compatible fish that are larger than they are.

Although 55 gallons is stated as the minimum tank size, 100 gallons (378 liters) may be wiser.  Maintain a steady temperature between 72˚ and 81˚F (22 to 27˚C).  There should be quite a bit of live rock that are formed into caves and crevices for the Sixline Soapfish to hide in during the day.  Some specimens may need live foods like feeder fish and glass shrimp etc., but are easily trained to eat bite-sized pieces of saltwater originated raw fish or shrimp.  They can be trained to eat prepared frozen/thawed foods.  They swim at the lower levels of the tank and good water movement to provide sufficient filtration is suggested.  Any light is acceptable, however a dimmer tank that does not have corals would be a better choice, unless most of the bottom of a reef tank is dark and shaded.

For more Information on keeping this fish see:
Guide to a Happy, Healthy Marine Aquarium

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Perciformes
  • Family: Serranidae
  • Genus: Grammistes
  • Species: sexlineatus
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  • Aquarist Experience Level: Expert
  • Aquarium Hardiness: Very Hardy
  • Minimum Tank Size: 55 gal (208 L)
  • Size of fish – inches: 11.7 inches (29.72 cm)
  • Temperament: Semi-aggressive
  • Temperature: 72.0 to 81.0° F (22.2 to 27.2&deg C)
  • Range ph: 8.1-8.4
  • Diet Type: Carnivore
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Habitat: Distribution / Background

The Sixline Soapfish, Grammistes sexlineatus, was described by Thunberg in 1792. 
This is the only fish in this genus.  The common names are Sixline Soapfish, Goldenstriped Soapfish, Lined Soapfish, Golden-Striped Bass, Radio Fish, Six-Lined Perch, White-Lined Rock Cod, Black and White Striped Soapfish, Grouper, Skunkfish, and Yellowstriped Soapfish.  These common names are all descriptive of the pattern, coloring or physical characteristics.   


Distribution – Habitat:
Sixline Soapfish are found in the Indo-Pacific, from the Red Sea to the Marquesan and Mangareva Islands then north to Japan’s southern tip and down to New Zealand and half way down both sides of the Australian Continent.  These fish inhabit coastal waters with corals and rocky substrates, and hide under ledges and in small caves during the day.  They can also be found in lagoon patch reefs, fore-reef slopes, reef flats, outcroppings and once in a while, in estuaries where the ocean meets the mouth of a freshwater river.  They are found at depths of 3.3 to 426 feet (1 to 130 m), with juveniles in shallow waters and adults in the deepest waters.  They feed on crustaceans like juvenile crayfish, shrimp and crabs.   Any fish the same length or smaller will be eaten.

They are found alone in the wild and should be kept singly in aquariums.  They may be similar to groupers in this aspect.  They have not been evaluated on the IUCN Red List for Endangered Species.

 Curiously, the Sixline Soapfish, when smaller, mimic the Black Striped Cardinalfish (Apogon migrofasciatus) and the Sevenstriped Cardinalfish (A. novemfaciatus).  Both the Sixline Soapfish and these cardinalfish inhabit similar hangouts, it is thought that either there is “strength in number,” or due to these cardinalfish’s small 3” to 3.5” size, they are fooled and make easy prey for the Sixline Soapfish!

  • Scientific Name: Grammistes sexlineatus
  • Social Grouping: Solitary
  • IUCN Red List: NE – Not Evaluated or not listed


The Sixline Soapfish adult has an elongated, robust body.  The color as an adult is brown with 8 or more, closely spaced horizontal white lines that are broken up into dashes from the area behind the gills to the tail fin.  The head, from the mouth to the gill plates, have white dots and possibly some dashes.  There is a double dorsal fin, with the first one having 7 spines, however the first and last spines are quite small.  The second dorsal fin is rounded, as are the rest of the fins, which are generally light brown.  They have a downward angled mouth which has large swallowing capacity, opening almost as wide as their body! 

Very small juveniles from .07”  (1.7 cm) are black with whitish yellow spots.  Juvenile Sixline Soapfish between 2 and 3.1” (5 to 8 cm), have 3 whitish yellow horizontal stripes over a dark brown body.  Once they grow to over 3.1” (8 cm) they develop 6 white stripes over a dark brown body.  Not until they are over 5.5” (14 cm) will they develop the adult pattern.  Juveniles have clearish fins that darken as they get older.  This fish grows to 11.7” (30 cm) and like groupers, may live up to 37 years.  

  • Size of fish – inches: 11.7 inches (29.72 cm) – 11.7” (30 cm)
  • Lifespan: – May be similar to groupers, which live up to 37 years.

Fish Keeping Difficulty

Like other Soapfish, the Sixline Soapfish os hardy, yet they are listed as best housed by “expert” fish keepers!  Transport, illness and inappropriate tank mates can result in death if they release all the toxins that their body slime always has present.  In larger tanks with good filtration, this is a little less of a concern.   However, if not an expert yet, an aquarist willing to go the distance will have success with this very cool fish.  Although older literature shows 55 gallons as the minimum, the newer thinking on the matter sets minimum tank size at 100 gallons.  This is not out of the question due to the nature of the fish, and risk of them soaping up.  This larger tank size will be a little more forgiving and possibly would allow enough time for the removal of all other inhabitants if the toxin is released.  This may not happen very often, but eventually the Sixline Soapfish will die of old age at least, and will emit the toxin and take out the entire tank.  Having a very good filtration system and Purigan or Polyfilters handy would be helpful.  Do not quarantine this fish.  Apparently, it is just too stressful and performing a temperature and pH adjusted freshwater dip just before putting them in the tank is usually enough.  It is suggested that your soapfish be the first fish added to your main display.  Any toxins emitted from stress should end up diluted and handled by 100 gallons until your Sixline Soapfish adjusts.  Once the fish is fully adapted, recognizes you as it’s food source, and becomes friendly, start to add other tank mates.  Adding this fish after other fish, may possibly end up in more stress and emitting of the grammistin poison.

  • Aquarium Hardiness: Very Hardy – Once acclimated, they are very hardy.
  • Aquarist Experience Level: Expert – This is due to the possibility of tank poisoning. Tank mates and habits must be followed to the “T” to prevent this.

Foods and Feeding

The Sixline Soapfish is a carnivore.  They may need live feeder fish or feeder shrimp to induce a feeding response.  Gladly, after a short time, they can be trained to eat small bits of fish or crustacean flesh that comes from saltwater sources.  These items can be obtained at the grocery store to help cut the expense of feeding this very hungry fish.  Some can be trained to eat prepared frozen/thawed foods and possibly large presoaked pellets (to expel all the air) on occasion.  Avoid silversides, since they do not have the nutritional value needed by your Sixline Soapfish.  While a juvenile will benefit with daily feedings, adults only need to be fed 2 to 4 times a week.  Do not be alarmed by their large distended belly, this is normal after eating a large meal!

  • Diet Type: Carnivore
  • Flake Food: No – Not satisfying enough for adults

  • Tablet / Pellet: Occasionally – Large pellets for carnivores; specifically, Spectrum
  • Live foods (fishes, shrimps, worms): Some of Diet – Small black mollies, small damsels and live shrimp to induce feeding.
  • Meaty Food: All of Diet
  • Feeding Frequency: Daily – Daily as a juvenile. Feed 2 to 4 times a week as an adult.

Aquarium Care

Reef tanks

  • Large Tanks 100 gallons and over, once water is aged and stable can be changed 10% bi-weekly to 20% monthly, depending on bioload.

Fish only tanks:

  • Large Tanks 100 gallons and over, once water is aged and stable can be changed 20% to 30% every 6 weeks depending on bioload.

For more information on maintaining a saltwater aquarium see: Saltwater Aquarium Basics: Maintenance. A reef tank will require specialized filtration and lighting equipment. Learn more about reef keeping see: Mini Reef Aquarium Basics.

  • Water Changes: Bi-weekly – 55 minimum (208 liters); however, 100 gallons (378 liters) would be better.

Aquarium Setup

Provide a minimum tank size of 55 gallons, although 100 gallons would be a better choice to dilute the toxins they carry in their body slime.  Use of good filtration can also help.  Do not put in a nano tank, even when small, and do not quarantine.  They need quite a few places to hide, so form live rock into caves and crevices that they can hide in during the day and use sand as substrate to mimic their habitat.  The less stress factors the better!  The temperature should be between 72 and 81˚F, with normal ocean salinity and pH between 8.1 and 8.4.  Although light is irrelevant since they hide during the day, a dimmer aquarium may be better than a bright reef.  Provide good water movement to help provide good filtration.  House alone in a community tank that does not have overly aggressive fish, or with fish, crabs and shrimp that are the same size or smaller.  

  • Minimum Tank Size: 55 gal (208 L)
  • Suitable for Nano Tank: No
  • Live Rock Requirement: Typical Plus Hiding Places
  • Substrate Type: Any
  • Lighting Needs: Any – Lower light levels would be better since they are nocturnal.
  • Temperature: 72.0 to 81.0° F (22.2 to 27.2&deg C) – 72˚ F (22˚ C) 81˚ F (27˚ C)
  • Breeding Temperature: – unknown
  • Specific gravity: 1.023-1.025 SG – Adults dwell in deeper waters in the ocean, which is a higher salinity.
  • Range ph: 8.1-8.4
  • Brackish: No
  • Water Movement: Any – Good water movement helps with filtration.
  • Water Region: Bottom

Social Behaviors

The Sixline Soapfish is peaceful to other fish, unless the fish is the same size or smaller, then it can become lunch.  They  have been known to eat their own kind as well!  Due to that fact, they are often listed as aggressive, which isn’t entirely accurate.  Semi-aggressive is more accurate since they do pose a threat to only bite sized fish.  They don’t pay attention to fish that are too big to swallow!  House as the only soapfish in the tank.  Even a male and female pair would not be a good idea since they are solitary in the wild.  

The Sixline Soapfish can be housed with any larger peaceful or semi-aggressive fish.  You will have to watch to see how other large fish react to your soapfish.  If you add a Triggerfish that is more aggressive, such as a Clown Triggerfish, and it starts to pick on your Sixline Soapfish, very bad things may happen!  Any fish should be added after your Sixline Soapfish is adjusted and happy.   You will be safe with peaceful groupers who are not overly territorial.  Tangs, large angelfish, pufferfish, semi-aggressive triggerfish, semi-aggressive eels and other large fish will be good companions.  Tobies, although they carry a toxin will be eaten by the Sixline Soapfish.

These fish will not bother corals.  They are what you consider an “aggressive reef” fish.

Inverts are okay except for crustaceans, such as shrimp or small lobsters and crabs, which are part of their diet.  Starfish are not bothered unless they are very small.  Chocolate Chip Starfish, for example, will do fine with your Soapfish.

  • Venomous: Yes – Can release toxins if stressed or if it dies
  • Temperament: Semi-aggressive – Peaceful to fish larger than they are, that cannot be swallowed.
  • Compatible with:
    • Same species – conspecifics: No
    • Peaceful fish (gobies, dartfish, assessors, fairy wrasses): Threat – As adults they can swallow any fish under 12” whole!
    • Semi-Aggressive (anthias, clownfish, dwarf angels): Threat – As adults they can swallow any fish under 12” whole!
    • Threat – As adults they can swallow any fish under 12” whole!
    • Large Semi-Aggressive (tangs, large angels, large wrasses): Safe – Only fish over 12” as adults and only added when they are larger than the Soapfish.
    • Large Aggressive, Predatory (lionfish, groupers, soapfish): Safe – Watch for aggression toward the Soapfish and remove promptly.
    • Threat – Can swallow even noxious fish whole!
    • Anemones: Safe
    • Mushroom Anemones – Corallimorphs: Safe
    • LPS corals: Safe
    • SPS corals: Safe
    • Gorgonians, Sea Fans: Safe
    • Leather Corals: Safe
    • Soft Corals (xenias, tree corals): Safe
    • Star Polyps, Organ Pipe Coral: Safe
    • Zoanthids – Button Polyps, Sea Mats: Safe
    • Sponges, Tunicates: Safe
    • Shrimps, Crabs, Snails: Threat – Will eat shrimp and crabs, may not eat snails.
    • Starfish: Safe
    • Feather Dusters, Bristle Worms, Flatworms: Safe
    • Clams, Scallops, Oysters: Safe
    • Copepods, Amphipods, Mini Brittle Stars: Safe

Sex: Sexual differences


Breeding / Reproduction


  • Ease of Breeding: Unknown

Fish Diseases

These fish are hardy, but the toxins they choose to emit when scared or sick is typically what will kill them.  Sometimes this can happen on the way home from the fish store.  Ask the fish store not to feed the fish for at least 2 days before transport for best results.  These fish do not ship or transport well, unless there is a good amount of water and oxygen.  If your transport of this fish from the fish store to your home results in an apparently almost dead fish, who obviously has released it’s own toxin don’t give up!  Do as one aquarist did and hold the fish (wear gloves), in front of the power head in the main tank to help oxygenate and clean out the toxins it expelled in the travel bag.  Never put travel bag water into the tank.  This aquarist took a few hours to see results!   His soapfish survived the ordeal, although it almost ended up in the toilet in the beginning! 

Soapfish should also be the first addition to your cycled main display to prevent the stress of being added into tanks with larger fish.  Do not use copper treatments, only quinine medications for Protozoan treatment.  Use a freshwater dip with the pH and temperature matched to the aquarium water, and skip quarantine.

For information about saltwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


These fish are found on line and are the lower middle average price for saltwater fish.


Animal-World References – Marine Fish