Aquarium Fish: Captive Observations of the Mimic Octopus, Thaumoctopus mimicus
Most people are familiar with the basic attributes of an octopus; eight sucker lined arms (or are they legs?), excellent eyesight, an ability to change skin color and the capacity to release ink when attacked by predators. Marine aquarists also know of the octopus’s relatively short lifespan, sensitivity to water quality problems, incompatibility with many other aquarium inhabitants and the ability to escape from many types of aquariums. One group of octopuses that are not routinely kept in aquariums are the tropical “long armed” species. Expensive and delicate, few aquarists have had the experience of working with these unique animals. Perhaps the most unique of this group is the mimic octopus, Thaumoctopus mimicus. This amazing animal is a frequent subject of nature shows and underwater photographers for its remarkable ability to mimic other aquatic creatures in order to avoid predation. This octopus has been reported to be an active mimic of venomous lionfish, deadly Laticauda sea snakes, poisonous flatfish, plus stingrays, jellyfish, sea anemones, and mantis shrimp – by one count, impersonating over 15 different species.
A Primer on Mimicry
- Active mimicry
- means that the animal changes its coloration and/or behavior to match that of another species, distasteful to predators.
- Batesian mimicry
- occurs when a relatively defenseless mimic assumes the form of a distasteful or venomous model.
- Mn mimicry
- happens when one animal with certain defensive powers mimics another distasteful model, such as the “spiky”, thick-skinned mimic filefish that mimics the poisonous toby pufferfish.
- Passive mimicry
- is seen when an animal resembles the model all of the time, and does not modify its behavior, such as the viceroy butterfly mimicking the monarch.
On the question of mimicry, it is possible that some observers have been presumptive when they began to attribute so many mimicking behaviors to this species. The original researcher states that this species performed a variety of different behaviors “several of which were clearly impersonations of venomous animals” (Norman et-al 2001). The term “several” probably does not imply the 15 or so behaviors reported by some people. For example, the “stingray model” is basically the same as the “flatfish model” just with one arm trailing to resemble the ray’s tail. Is this a case of active mimicry of a stingray, or was the octopus in that case just a bit lazy and let the arm dangle a bit? The sea snake mimicry is the most compelling case, with the mimic octopus extending two striped arms in opposite directions, while the body and other arms of the octopus remain buried in the substrate. Most telling is the observations made by Norman et-al that show that the octopus performs this mimicry only when attacked by damselfish – a favorite prey item of the sea snake. Of all the possible models, that of the lionfish is the one most often described. A mimic octopus swimming with its arms extended and a strong striped color pattern certainly does resemble a lionfish. Is this active mimicry, or are both animals simply using similar aposematic coloration to warn off potential predators? These questions cannot easily be answered by captive observations because they require watching the model and the mimic, as well as the interactions of both to other species. Still, captive observations do indicate that some of these proposed modeling behaviors may be more happenstance than anything else. It may also be that the mimic octopus is actually a venomous species, and its bold striped pattern is presented for the same reason as that of the lionfish – to warn potential to give them a second thought before attacking.
One activity noted in a captive animal was its apparently “playing dead” behavior. During a photographic session to illustrate this article, a mimic octopus suddenly flipped over onto its back and rolled tentacles back in a tight ball. Observation of the resulting photograph shows that the octopus was carefully watching the photographer while it was feigning death. Even this apparently obvious mimic behavior must be questioned. While some animals, such as the hognose snake do play dead when attacked by predators, this is a dangerous ruse, as some predators simply take that as an open invitation to subsequently eat the passive animal. Octopus are very complicated creatures – what if this “playing dead”, which seems to aim the animal’s beak towards the attacking threat, is actually done to bring its venom into play as a defensive weapon? Toxicity studies must be performed on this species before the exact reason behind many of these behavioral activities can be determined.
Fish or Fishes, Octopus or Octopuses?
Some debate has transpired over the proper plural name for more than one octopus. In roughly descending order of common use, there are: octopuses, octopus, octopi, and octopodes (or octopods). Octopuses is commonly given as the most proper plural name, as derived from a Latinized Greek word. Octopus is generally used as a plural only when discussing octopus as a menu item, as in “Fresh octopus sold in fishmarkets is often used as sushi.” Octopi is not correct grammer for a Latinized Greek word. Most scientists reserve the use of Octopodes when discussing all members of the order octopoda at the same time.
Despite warnings by some pundits, the captive care of the mimic octopus is rather straightforward. They are best kept in an aquarium by themselves, with only peaceful, sedentary invertebrates such as sea stars or soft corals as tankmates. Due to their propensity to dig in the substrate, the aquarium should not rely on undergravel filtration, as the octopus may be able to dig down and get underneath the filter plate. Obviously, the aquarium needs a well-established bio-filtration system with reasonable water quality. Reports vary regarding this species ability to escape from an aquarium. Some octopuses, such as Octopus vulgaris are great escape artists, able to push aside heavy lids in order to escape. The long, spindly arms and relatively weak suckers of the mimic octopus seem to indicate that it may not be able to escape in this fashion very easily. With the cost of the mimic octopus as high as it is, the prudent aquarist will however err on the side of caution and keep the aquarium tightly covered. Remember that octopuses can squeeze their bodies through tiny openings (down to holes about the diameter of half the distance between their eyes). There is also debate about lighting requirements for this species. Some aquarists insist that like most octopus, they should be kept in dimly lit aquariums. Other people point out their diurnal, shallow water habits suggests that bright lights are not a problem for mimic octopus. While this debate is being resolved, it appears that a compromise will work well; standard fluorescent lighting at about two watts per gallon for 12 to 16 hours each day is appropriate for this species.
What’s in a Name? The Wunderpus
A striped octopus species very similar to the mimic has recently been given the scientific name of Wunderpus photogenicus. This fanciful name was approved for use in naming this species by the International Commission on Zoological Nomenclature. Humorous scientific names for animal are not unknown, science geeks often cannot resist having a bit of fun. Here are some other examples:
- Abra cadabra (Eames & Wilkins) 1957 (a clam)
- Aegrotocatellus Adrian and Edgecombe, 1995 (trilobite) Latin
for "sick puppy".
- Ba humbugi, a snail from Fiji.
- Bobkabata kabatabobbus Hogans & Benz, 1990 (parasitic
copepod) Named after parasitologist Bob Kabata.
- Corydoras narcissus Nijssen & Isbrucker, 1980 (catfish)
Named "narcissus" because the discoverers insisted that the describer
name the fish after them.
- Galaxias gollumoides (fresh-water fish) Named after Gollum because it has large eyes and was found in a swamp.
- Ittibittium, a genus of mollusks that are smaller than those named Bittium.
- Mackenziurus johnnyi, M. joeyi, M. deedeei, M. ceejayi Adrian and Edgecombe, 1997 (trilobites) As any one who went to high school in the 1970’s can tell you, they are named after members of the punk rock group, the Ramones.
- Polypterus mokelembembe Schafer and Schliewen 2006 Named for the cryptozoological Congolese dinosaur-like creature Mokele-mbembe
- Ptomaspis, Dikenaspis, Ariaspis (Devonian armored jawless fish) Remove the suffix “-aspis” to see the joke.
Is a zebra white with black stripes or is it black with white stripes? Actually, using that question is one way to tell apart the closely related mimic and Wunderpus species. In their typical coloration, the mantle of the mimic octopus has a light background with mottling and stripes of a darker color (white with black stripes), while the Wunderpus has a reddish brown background with distinct cream spots and bars (brownish red with white stripes). Of course, given the variability of their coloration, it can be difficult to tell one from the other at certain times. One additional clue that can be used is that the eyes of the Wunderpus are usually raised on stalks.
A Case Study of one Captive Mimic Octopus
This animal was collected in Indonesia in early December, 2006 and imported by a wholesale marine aquarium firm in Los Angeles. It was purchased sight-unseen (not recommended) and shipped via overnight courier and placed into a 40-gallon aquarium.
The octopus arrived in a moderately stressed condition (the shipping water was clouded with fecal matter). It seemed to acclimate well, but it initially refused all manner of live foods (shrimp, crabs, snails and small fish). Surprisingly, it accepted frozen krill by the third day when offered it on a broom straw by an aquarist desperately trying to get it to feed. Other seafood items were eventually accepted, including bits of shrimp tail meat and pieces of smelt. Reports of mimic octopus feeding on snails and hermit crabs may not apply to captive animals (at least none have reported to feed on these items in captivity). When hungry, this specimen would perform two foraging behaviors noted in wild specimens. The first is “speculative probing”, where the animal crawls along the bottom, using the tips of its arms to probe into crevices and down into the substrate looking for food. The second behavior is called “web-casting” and consists of the animal standing up on its arm tips and expanding the webbing on the arms to form a sort of net. The arm tips are then used to flush any prey items up into the umbrella-like net (Hochberg et-al). Since this animal was always fed frozen seafoods on the end of a broom straw, these foraging behaviors were only seen when the animal was very hungry, and of course, did not produce any food for it.
Possible signs of senescence were seen in this specimen as time went on. These symptoms included a cataract in one eye and abrasion to the posterior of the mantle (presumably from the octopus jetting backwards into objects in the aquarium). At the time of this writing, this animal was otherwise still eating and behaving normally, so it is unsure how these issues will progress as the animal ages.
Questions remain about the activity patterns of the mimic octopus in both the wild and in captivity. Some reports indicate that this species is mostly nocturnal (as are many other species of octopus) while other people report that the species is crepuscular – most active in the lower light levels of dusk and dawn. However, many videos and photos taken of mimic octopus in the wild show that they are active during daylight hours, an activity which is termed diurnal. Because this species has such a wide range of interesting behaviors, a time budget study was undertaken with this captive specimen using what is known as an ethogram (A way to scientifically quantify an animal’s behaviors). In these types of studies, all of the possible behaviors of a particular species are first identified through observation, and then the time an animal spends performing each of the behaviors is recorded. For the mimic octopus, nine primary captive behaviors were identified, and then the octopus was monitored for the time it spent performing each activity throughout a series of 24-hour periods. The preliminary results indicated that in captivity, the mimic octopus is mostly diurnal, so for this study, fewer observations were taken at night. Ten times each day for ten days, the activity of the mimic octopus was recorded. The results are as follows:
|Bold coloration, with webbing extended on arms||10|
|Bold coloration, flat on the bottom, not moving||5.7|
|Bold coloration, crawling, digging, exploring||18.4|
|Pale coloration, stationary, at rest||10|
|Pale coloration, crawling||10|
|Pale coloration, perched at rest||14.3|
|Actively swimming, arms trailing||2.3|
|Actively swimming, arms in an oval||2.1|
|Sleeping, eyes closed, pale coloration||22.9|
|Gathering or consuming food||4.3|
From this preliminary data, it seems that in captivity, this mimic octopus slept about 23% of the time, was is in its bold brown and white striped mode for one third of the time and spent one third of the time in its pale coloration mode. The balance of the time was spent either feeding or actively swimming. The relatively high percentage of time spent in the pale mode presents an interesting hypothesis. There are reports from the wild of another species of octopus dubbed the “blandopus”. This animal is reported to physically resemble the mimic and Wunderpus species, except that it has a plain coloration. Could it be that reports of this species are actually sightings of mimic octopus in the non-striped mode? A series of underwater photographs taken by Andrea and Antonella Ferrari show just that. What looked at first like a chance encounter and possible fight between a mimic octopus and a “blandopus” turned out to be a male and female of the same species involved in courtship and mating activity. Later in the photo sequence, both octopuses assume the typical bold color pattern of the mimic octopus. This begs the question, how many reports of divers seeing a “blandopus” are actually seeing a mimic octopus in its pale coloration phase? The implication of this may be that the mimic octopus is more common than is commonly thought, but that it is just being mistaken for a different species.
Both the mimic and Wunderpus have been collected for the pet trade since at least 1985 (Hochberg et-al 2006) but it has only been in the past four years that they have become a bit more widely available. Still rare in the pet trade and very expensive, they should only be acquired by advanced hobbyists or public aquariums who understand the ramifications of buying an animal whose natural lifespan may be measured in months, or even days (if acquired as a mature adult to begin with). With a retail cost of $250 to $500, one needs to be certain of their ability to care for the animal properly. Since many of the reported deaths of these animal in captivity occurred within a week of their importation, shipping and/or collection stress obviously plays a major role in a given animal’s long-term survivorship. For this reason, one should never buy a mimic octopus sight unseen, always watch it at the pet store for a few days and be certain that it is eating well before buying it.
|Mimic||4+ months (still alive)||frozen seafoods||40 gallons|
|Wunderpus||11 months||live foods only||15 gallons|
|Unknown||4 days||live food only||Unknown|
|Wunderpus||6 months||live food only||Unknown|
|Wunderpus||9 months||Frozen seafoods||“Small”|
|Wunderpus||5 days||Live food||Unknown|
|Mimic||< 1 month||Refused all food||50 gallons|
|Mimic||7 months||Frozen shrimp||50 gallons|
|Mimic||5 months||Shrimp, live & frozen||Unknown|
|Mimic||1 day||Refused all food||Unknown|
|Mimic||~ 5 days||Refused all food||Unknown|
|Wunderpus (3)||each < 4 months||Unknown||Unknown|
Of the 15 animals shown in the data table under the longevity column, the average captive lifespan for the group was approximately four months. While this may seem an incredibly short time, remember that many of these were collected as adults, and were ending their natural life spans anyway. To put this further into perspective, mortality rates of typical marine fishes in the pet trade can range from 30 to 60% in the first 30 days following importation from the Philippines and Indonesia (Hemdal 2006, and unpublished data).
It would be remiss not to mention that a few people feel very strongly that due to the apparent rarity of these species, they should not be collected at all. This presumption that the pet trade will adversely affect wild populations of these octopuses may or may not be valid. The mimic octopus may well be rare in the wild, or it could be that it is just rarely seen by divers because it frequents habitats that are rarely explored (muddy areas at the mouths of rivers is one habitat of this species – almost never visited by divers).
The pet trade has seriously affected populations of some traded species such as the colored carpet anemone (Hemdal 2006) but the case of the mandarin dragonet should also be considered. The first mandarins became available in the Midwest in the early 1970’s and cost upwards of $300 at the retail level. Within a few months, the price had dropped to $150, and then dropped again to around $20 – where it has remained relatively unchanged for the next 35 years. While this is obviously a case of a “rare” animal supporting a commercial trade that seems sustainable, bear in mind that the mimic octopus may or may not follow this model. Aquarists should think long and hard before ever acquiring one of these creatures. Public aquariums have “Institutional Collection Plans” that are used to analyze the appropriateness of every animal they acquire. If they cannot meet an animal’s needs, or if there are other compelling problems regarding the acquisition, they will not acquire the animal. Home aquarists are advised to “mimic” that behavior as well!
A female mimic octopus laid eggs after being in captivity for four months. Presumably, the eggs were not fertile as the octopus was acquired as a juvenile, and it is unlikely that mating had occurred prior to the animal’s capture. The egg capsules were approximately 3 mm long, but as they seemed infertile, this size may not reflect that of normally developing eggs. In one still photograph where the egg mass was partly exposed, 197 eggs were counted. The total number of eggs in the entire brood was higher, possibly over 300. The eggs were arranged in three or four strings, and were carried by the female rather than being deposited in a nest as with many other species of octopus. Position of the egg mass varied depending on the circumstances. When the octopus was active, the eggs were carried within the arm crown and held in place by the suckers. This is the same behavior reported for Wunderpus photogenicus (Miske and Kirchauser 2006). This octopus continued to feed after laying its eggs, and when it was offered food, it moved the egg mass down the length of two or three arms, leaving its buccal cavity open to ingest the food. While at rest, the octopus sometimes moved the egg mass to the end of its arms, holding them lightly in place with two or more arms.
- Hemdal, J.F. 1989. Mimicry in marine fishes. SeaScope 6:2‑3.
- Hemdal, J.F. 2006. Advanced Marine Aquarium Techniques. 352pp. TFH publications, Neptune City, New Jersey
- Hochberg, F.G., Norman, M.D., Finn, J. 2006. Wunderpus photogenicus n. gen. and sp., a new octopus from the shallow waters of the Indo-Malayan Archipelago (Cephalopoda: Octopodidae) Molluscan Research 26(3): 128-140
- Norman, M.D., J. Finn, and T. Tregenza. 2001. Dynamic mimicry in an Indo-Malayan octopus. Proceedings of the Royal Society of London B 268(Sept. 7):1755.
- Miske, V. & Kirchhauser, J. 2006. First record of brooding and early life cycle stages in Wunderpus photogenicus Hochberg, Norman and Finn, 2006 (Cephalopoda: Octopodidae) Molluscan Research 26(3): 169-171