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Keeping Lionfishes and their Scorpaeniform Kin

Keeping Lionfishes and their Scorpaeniform Kin
Part 1: Selection, Care, and Compatibility

By Anthony Calfo and Robert Fenner

Rhinopias are some of the most magnificent fishes in the sea. They fascinate any aquarist privy to a glimpse of these uncommon beauties.  Retail prices for such specimens can exceed $1000.00.  Photo by Anthony Calfo

Overview:  Divers and aquarists alike quickly recognize the need to approach and handle these fishes with distance and respect.  The etymology of the Order says it all:  scorpion-form (from the Greek "skorpios" and Latin "forma").  While most aquarists cannot name many more members of this Order than the popular Lionfishes, this is a very large group of fishes!  Once you start looking into them, it just gets larger and larger.  Also known as "Mail-Cheeked Fishes," the Order Scorpaeniformes includes some 35 families, around 300 genera, and over 1,000 species including venomous and non-venomous members.  Species of this Order occur in fresh, brackish, and marine waters.  Marine types live in most oceans of the world, in most habitats, and over a very wide range of depths.  Due to their generally large sizes, plain or cryptic visage, and low activity, only a smattering of these families and species make their way into the pet-fish trade.  Still, with strict caution while handling the venomous ones especially, aquarists willing to accept the unique challenges of feeding, stocking, and husbandry can keep more than a few members of this Order.  Some are even suitable for beginners if given enough space and live food when necessary.  Husbandry for these fishes usually requires oversized filtration, large aquaria, above average water quality and frequent water exchanges.

Scorpaeniform fishes occur in a wide array of colors, shapes, and crypsis.  Although some members of the Order are non-venomous, certain family members are some of the most venomous fish in the world! Photos by Anthony Calfo.


Features unique to many in this group warrant special attention.  As with other scaleless or small-scaled fishes, Scorpaeniform fishes can be very sensitive to water quality (elevated ammonia in shipping containers, low dissolved oxygen, etc.) and contaminants.  Metals and medicines in the water have been historically, although variably, risky here too. Though some specimens clearly demonstrate no less tolerance for common medications, for example, than large-scaled fishes, we will advise you to error on the safe side by using half doses for extended times.   You should also avoid organic dyes and metals altogether, such as Malachite Green or heavy copper.  Copper treatments in central holding systems can be an issue with merchants that do not house Scorpions and other sensitive fishes separately.  To put a fine point on this concern, we are not saying that metals or organic dyes cannot be used, but suggest that they be applied in small frequent doses (versus large spikes), dilute if necessary, and always with close supervision on potentially sensitive fishes like some of the Scorpaeniformes.

New imports are not likely to be any more active than typically lazy, well-established specimens.  They are ambush predators and generally "act the part."  Within this Order, however, the Pteroinae  Lionfishes are somewhat of an exception and will cruise the reef actively, sometimes even by day, looking for prey rather than lay in wait like most Scorpion-, Stone- and Rockfishes.  Nonetheless, this Order overall really is quite sedate.  This behavior runs right down to their rates of respiration, which are slower than other reef fishes.  For their low activity and intent to remain inconspicuous, mail-cheeked fishes breathe at a relatively slow rate; their gill movements are about thirty times per minute (that’s only half of some typical reef fishes!).  Be mindful, however, that candidates are not instead making very labored or exaggerated gill movements, which can be a distinct sign of trouble.

Harkening back to concerns with scaleless and small-scaled fishes, we advise you to examine candidates' bodies and fins carefully.  Holes in the fins can heal easily, but broken spiny rays or sores and discolorations on the body are cause for not purchasing any animals in that system. Arguably, wounds and infections on Scorpaeniformes are more susceptible to progressing rapidly than with other fishes.  Some species with elaborate crypsis and ornate fleshy extensions have a lot of soft tissue and spines easily damaged in shipping (i.e., leafy appendages, thin webbing between spines, etc.).  Superior water quality in the merchant's display and in your quarantine tank for the first weeks after import will be crucial to help reduce the risk or spread of infections and disease.

Lionfishes and their kin can be somewhat prone to the rapid spread of bacterial infections from injury to soft tissues in transit.  Be prepared to treat such wounds in quarantine with proper antibiotics like Furan-based medications and good water quality.  Do small daily water changes in QT for the first week or more.  Photo by Anthony Calfo.


The appetite of most new imports should not be very different from what you can expect once they settle in.  Although many will demand live shrimp or small fishes initially, and may continue to do so indefinitely, it should rarely be difficult to initiate a feeding response.  Unless they’ve recently been fed, they will show interest in food offerings.  Play it safe and don’t buy fishes that don’t eat.  If you really want a specimen that is not feeding, ask the merchant to hold the fish (a deposit may be necessary and appropriate) for several more days to a week or more as needed.  While larger sedentary predators do not require daily feedings, small feedings several times weekly are about right.  Do not fool yourself into taking home a non-feeding fish with the hope and belief that it will be more likely to eat with your improved care and attention.  The additional move so soon after the last (import) could put it off its feed.  In fact, very large, well-fed individuals have been known to fast for weeks after being disturbed, as with a big décor change or other traumatic events.  Still, take heed of this admonition:  only buy fishes that feed heartily in your dealer's tanks.


It should go without saying that you should NEVER take your eyes off of these fishes when your hands are in their aquarium.  They can “sneak up” on what they perceive as a risk and inflict a painful wound in seconds. Distracted aquarists performing routine functions like scraping algae may drive a sweeping hand or arm down upon the venomous spines.  And frankly, some Scorpionfishes can be sufficiently irritated or threatened to charge offensively.

The actual environments of these fishes and their provision in captivity are highly varied.  Many species are sedentary, sitting on rocks or upon the seafloor, blending in with their personal camouflage of colors or skin flaps with possible algal and sponge growth settlements.  Some sway back and forth (e.g., Leaf Scorpions, Rhinopias spp.) to blend in with surging weedy habitats.  Others burrow partially or fully under the sand (e.g. reef Stonefish, Devilfishes) while living on open flats.  The bold Pteroinines (Turkey-, Zebra-, Lionfishes), so popular with hobbyists and public aquariums alike, stay out and about for much of the day.  But all members of this Order should be provided with a dark area of the tank to call their own - ideally, a large enough cave that they can get out of the light entirely if they wish.  Scorpaeniformes have crepuscular or nocturnal tendencies and feeding habits - more about feeding later in this chapter.  For aquarists that take the time to research exactly where their specimen comes from on the reef, the rewards can be rich in observing not only initial transformations of color and pattern to exploit their cryptic evolution… but possibly even the growth of (more) elaborate appendages and extensions, as with leafy and weedy species.  So get thee to a planted refugium!

Housing Lionfishes and Kin

Some other writers have suggested that it’s “okay” to place these fishes in small volumes of water (20 gallons for small species, 55 for larger ones) due to their sedentary natures, but please don’t do this!  After many years of being in the service side of our hobby, I have seen many systems with predatory fishes crash.  This is often caused by poor alkaline reserve, and  too much “metabolite” (heavy bio-load from heavy predators).  You can be assured that, other than good filter design and maintenance, providing extra room is your best guarantee to avoid losses and enjoy fishes that thrive and not just merely survive.  The larger space will also (importantly) give you more room to avoid being stung while working in the tank.   It seems strange to us to even feel the need to mention these realities, yet we see it time and again, having spent our lives in the hobby and industry of aquatic science.  It simply defies explanation, beyond the humane treatment of animals, from a husbandry point of view to condone or recommend the keeping of fishes that have potential growth to an adult size in an aquarium that is only as wide as that potential and not more than two to three times as long.  We cannot offer an "inches of fish, per gallon of water" rule of thumb with most any fishes, not the least of which Scorpaeniformes, due to the variety of techniques and schedules of feeding, husbandry, and hardware of various aquarists, etc.  What we can tell you is to be generous on the size of display aquariums and provide oversized filtration components for these "heavy load" fishes.  Even the very smallest species of Scorpionfish will likely require a minimum aquarium size of 50 gallons (~ 200 liters), and the popular Pterois volitans lionfishes will require very long aquariums (>6 feet/2 meters) for growth, with less risk of stunting or dying prematurely as with smaller tanks (under 75 gallons).

With an adult size of over 15" (38 cm.), Pterois volitans lionfish need a lot of swimming room… and what regal animals they are gliding in mid water!  We recommend a minimum six foot long aquarium (over 200 gallons/~750 liters) for this species at adulthood.  Photo by Anthony Calfo.


Lionfishes and their relatives have surprisingly specialized diets.  That is to say, while they are highly predatory and most will snap at anything small enough to ingest (and some things that are not!), their long term health and survival in captivity is crucially dependant on finding or being offering the right kinds of food to satisfy their specific nutritional needs.  In addition to fish, shrimp, and crabs, various Scorpaeniformes feed upon jellyfish and medusae, polychaete worms and even each other (cannibalism is not excluded in this Order by any means).  One of the easiest ways to  determine fishes' dietary needs is to research gut analysis for the target specimen; databases like and others, along with specific papers when available, detail the nature of diets for numerous species.

Aquarists frequently underestimate the importance of doing this, so we continue to have problems with long term vitality, if not survival, of species kept on unnatural diets.  In the case of mail-cheeked fishes, any old meat will not simply "do."  Much like humans, just because a fish eats certain foods doesn't mean those foods are necessarily good for them!  This sad reality plays out time and again with the Lionfish sub-family and their kin.  Many, many Lionfishes meet their death from a categorically inappropriate diet of “feeder” freshwater goldfish or the like, which are expensive, hard to digest, cause for “fatty degeneration” of internal organs, are inconvenient… and, in a word, are “bad” for them.  Don’t fall into the trap that your predators “need” feeder goldfish (where would they get these in the wild?) or cannot be trained to take killed prey and prepared foods. Pterois lionfishes and many of their relatives can be trained to even take dried carnivore food sticks or pellets!  Make no mistake that neither these nor any such predator specializes in wasting energy to catch the fastest and hardest to capture prey.  Please!  They seek the young, slow, weak, dying, or otherwise unaware specimens.  In captivity, however, most will adapt to killed or prepared foods (mostly thawed frozen meats of marine origin).

Above all, freshwater prey items are nutritionally deficient and will lead to the death of your marine predator in time.  Merchants and aquarists alike that have let their predatory fishes "train" them into thinking freshwater feeder fishes were good, necessary, or all that would be accepted need not wonder anymore why, after a year or two, the predators begin to suffer strange ailments.   These ailments include symptoms like renal/vision failure ("they sense the food in the water, but seem like they cannot see it clearly…snapping short and missing?") , or they appear to be unable to swallow the old familiar prey as if they have a "lump" in their throat (goiter, swollen thyroid).  Chalk it up to dietary deficiencies or inadequacies (like thiamin deficiency induced by a staple of feeder goldfish) taking its toll over time.  You should be determined to offer a wide variety of thawed fresh-frozen meats, dry, or otherwise prepared foods when possible and gut-loaded live prey if absolutely necessary.  Identify if your species favors arthropods (shrimp, crabs, and the like) or fishes, and adjust the given diet accordingly.

Food size is more important with fishes from this group, than with others.  What we have here, by and large, are gulping predators.  It is not uncommon in the wild or aquarium alike for a Scorpionfish to attempt to swallow prey that is too large and die in the process.  Although the advice might seem obvious, this concern speaks largely to tankmates, if any, in the company of mail-cheeked fishes.  Some gulping predatory fishes are legendary for their ambition (and often times success) at eating prey nearly as long as themselves!  Hobbyists are often surprised by the things that they hear, see and read about Scorpionfishes trying to eat – like hermit crabs. Now at first it might not seem so surprising that these dedicated shrimp and crab eaters would take a hermit crab.  What's amazing is that they will try to eat the whole crab – shell and all!  Ouch!  Talk about roughage.  There are other fishes as tankmates that present unique challenges or risks, like those with very spiny aspects about the head and gills, which can lodge into the mouth of an ambitious predator, killing both fishes out of fatigue and exhaustion if nothing else, in an unsuccessful attempt to make or break the "greeting."  In the confines of an aquarium, tragedies like this should never happen when aquarists are mindfully conservative about the things that go into the tank (food and tankmates). Small frequent feedings (2-4 times weekly or very tiny amounts daily) and very large, non-threatening tankmates are in order.  Popular staples include thawed fresh-frozen krill (freeze-dried will be accepted too by some), raw and whole cocktail shrimp (as in, shell-on and not gutted, but cut in pieces if necessary), various marine fish meats, live grass shrimp or crayfish, and even live earthworms for the occasional treat for dedicated polychaete feeders.


For all of the talk and warnings about Scorpionfish being “big-gulpers” that can swallow surprisingly larger fishes, they are remarkably vulnerable to some very common and seemingly non-threatening reef favorites.  It's still true, of course, that they should not be trusted with anything smaller than their (over-stretched) mouths can handle.  To be conservative, make sure all tankmates are at least twice as long as the Scorpaeniform in residence.  Lionfish in particular may sting their tankmates with their long spines in the inevitably crowded confines of an aquarium.  Victimized fishes may swim or become spooked into the waiting spines of a Lionfish or the envenomation can occur by attack under threatening circumstances. Erratic swimming, twitching, and sudden death will usually occur within thirty minutes of an effective sting.  But most mail-cheeked fish species are more likely to get picked on by other fish tankmates than vice versa. Turn about, as the saying goes, is fair play, and despite their spiny and venomous natures, Scorpionfishes do have their predators.  Of the threatening types that they’re likely to encounter in the wild, these include Sharks, Groupers, Frogfishes, and Moray Eels.  Perhaps more commonly, however, in captivity are prolonged, harassing attacks by "nippy" fishes like large Angelfishes, Butterflies, Triggers, and Pufferfishes.

There are also instances of intraspecific aggression in these fishes, often with apparent males facing off, directing venomous dorsal spines and stabbing each other.  These cases are uncommon, but require the separation of individuals if observed.  It's not hard to make a case for keeping most Scorpionfishes with few if any other tankmates.  While Lionfishes are somewhat of an exception and can make tolerant if not agreeable tankmates for large community fish aquariums, the most popular species used in the hobby, Pterois volitans, simply gets too large for most home-sized aquariums with a number of other fishes. And so, while their needs and husbandry may be underestimated or understated at times… their beauty never is.

Part II will examine the various species commonly encountered in the aquarium trade along with eye-popping photos.  Don't miss the next issue of Conscientious Aquarist!

WWM about Lions & their Relatives

Related Articles: Lionfish & Their RelativesThe Mystery of the Atlantic Pterois Lionfishes, by Anthony Calfo, Spiky characters; An introduction to the spiny, sluggish oddballs of the families Batrachoididae and Tetrarogidae by Neale Monks,

Related FAQs: Lions 1, Lions 2, Lions 4Lionfish Selection, Lionfish Compatibility, Lionfish Feeding, Lionfish Disease,

Taeniatus triacanthus off Taveuni, Fiji


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