Mermaid Care

by Jonathan Crowe

Few activities are more controversial than the keeping of mermaids (Atargatis havfruensis) in captivity. Despite being listed on Appendix I of CITES, their protected status in nearly every jurisdiction in the world and their extraordinarily challenging care requirements—to say nothing of the risks they pose to their keepers’ safety—they continue to fetch exorbitantly high prices on the black market.

Conservationists are divided on the ethics of providing care advice for this critically endangered species. One school of thought holds that mermaids should not be kept, full stop; providing information only encourages mermaid keeping. The other argues for harm reduction. The U.S. Fish and Wildlife Service estimates the number of mermaids in private collections at between 200 and 500 worldwide. Most are kept in dangerously substandard conditions. Providing basic care information would therefore go some way to improving the quality of life for those mermaids yet to be found and recovered by the authorities. Publicizing the substantial care requirements may also dissuade prospective keepers from acquiring a mermaid in the first place. We subscribe to the second view. A brief précis of mermaids’ captive care requirements follows.


Mermaid sightings in the wild are infrequent. Solitary and pelagic, mermaids seldom congregate and rarely approach boats or the shore. Most mermaids enter the exotic animal trade by way of rocky islets and skerries, where they are occasionally found in what collectors have described as a state of repose, combing their long tresses.

This vivid image is a staple of the enduring mythology surrounding this species, but it’s anthropomorphic nonsense. Mermaids are teleost fish. Their “hair” is a mass of several kinds of epithelial cells that collectively serve as both gills and sensory organs; they’re the mermaid equivalent of a lateral line. Mermaids stranded on rocky islets are simply suffocating: unable to breathe or return to the sea, they groom their “hair” with their unusually humaniform pectoral fins in an attempt to expose more of their gills’ surface area. This state of distress makes them quite tractable at the point of capture (as does the use of cobalt chloride), but contributes to their poor survival rate in captivity.

It’s unclear why mermaids strand themselves: is it accidental, or the result of some unknown self-destructive impulse? One possibility is that human activity in the oceans has been disrupting mermaids’ unusually delicate sensory organs, much as shipping noise has been found to disrupt whales’ communications networks: mermaids strand themselves because they can no longer bear the overstimulation. More research is needed to confirm this hypothesis.


Extremely fast swimmers, mermaids travel thousands of kilometres of open ocean in search of food sources (see below). Mermaid keepers consistently underestimate, by several orders of magnitude, just how immense the enclosure must be. While Olympic-size swimming pools have been used as makeshift holding tanks by mermaid rescue organizations, they do not represent even the barest minimum enclosure size; only the largest aquariums, with tanks holding more than five million litres of seawater, have had any success in terms of short-term survivability.

But simply providing a large volume of water is insufficient. For a mermaid to thrive, dissolved oxygen, pH and salinity levels must be calibrated precisely. Currents must be artificially generated: mermaids do not last long in stagnant water. Because of mermaids’ profoundly sensitive “hair,” electrical, chemical and auditory disruptions often prove fatal. In sum, mermaid requirements exceed even those of great white sharks, a species whose failure to thrive in captivity is well-known in aquarium circles.

Which is to say that the floor-to-ceiling aquariums installed in many keepers’ bedrooms—the so-called “boudoir aquariums”—provide only a fraction of the space required for a healthy mermaid.


Mermaids are active hunters, predating on most species found in the epipelagic zone. Staples include oilfish and smaller scombrids, as well as pelagic sea snakes. In captivity, live food must be provided; a varied diet is essential to avoid vitamin B1 deficiencies. Wild mermaids also occasionally supplement their fare with seabirds: a mermaid is capable of breaching three metres into the air to catch birds on the wing. This is aided not only by their unusually humaniform pectoral fins, but also by extraordinarily strong teeth and jaws; a mermaid’s mean bite force of 3,000 newtons is one-fifth that of a saltwater crocodile and is capable of shearing off human fingers—or any other appendages brought near the mouth.


Mermaids’ anterior resemblance to humans is an accident of convergent evolution. Their reproductive cycle is entirely piscine, with one caveat: mermaids are believed to be parthenogenetic. Only female mermaids have ever been captured. Poor survival rates have prevented observation of a complete reproductive cycle in controlled conditions, but on the three occasions when mermaids have spawned in captivity, the spawn emerged already fertilized.

It goes without saying—or it should—that, despite urban legends and several unverified (and long-debunked) accounts on the internet, human males are not a necessary part of the mermaid reproductive cycle.

Relationship with Humans

Mermaids are solitary creatures that have little need for social contact with one another, much less with human beings. They prefer to avoid human contact. Humans, for their part, bewitched by centuries of myth and fairy tales, do not share that aversion. It is important to emphasize this fact: mermaids are wild animals. They are not mythical creatures. They do not wish to be taken from the sea. They do not look for princes to fall in love with. They will certainly not fall in love with lonely rich men who install fish tanks in their bedrooms. They have no interest in human males at all.

You’re thinking of sirens.

© Copyright Jonathan Crowe

Jonathan Crowe blogs about maps at The Map Room. His essays and reviews have been published by AE, The New York Review of Science Fiction, Strange Horizons, and A former historian, civil servant, snake breeder, reporter, and fanzine editor, he lives in Shawville, Quebec. Visit his website at

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