There is no such thing as an extremely small shark species. There are, however, smaller shark species within the range of adult shark sizes. The truest small sharks, such as the dwarf lantern shark (Etmopterus perryi), which grows to just over 7 inches, are not available to aquarists. They live in deep ocean habitats and would not be suitable for captivity because of the physical characteristics of their natural environment.
When it comes to small sharks available to aquarists, some species will readily acclimate to the confines of a larger home aquarium. Before we take a look at some of the most aquarium-friendly small shark species, we need to go over the basics of shark care.
For our purposes, size refers to both how large the shark species you choose will be as an adult and how large an aquarium you will need. There are a number of shark species that will do well in a home aquarium as juveniles but will outgrow almost any home tank. For example, young nurse sharks (Ginglymostoma cirratum) make wonderful aquarium pets, but they typically attain adult lengths in excess of 10 feet.
It's essential when looking for a shark for your aquarium that you consider the maximum reported length of the species, which represents the largest specimen ever measured. Not all members of a species will attain that size, but it's also possible that a rare specimen may exceed the measurement. Although length data are very limited for some shark species, the listed maximum length for a species will give you a good idea of the space requirements for a given shark. Most of the species I consider suitable for a home aquarium do not exceed 40 inches.
Epaulette sharks will reproduce in large home aquariums. Photo by Scott. W. Michael
Not only are the suitable species smaller in length, they also have different lifestyles than the animals that most of us think of when it comes to sharks. The best aquarium sharks are bottom-dwelling species that live on coral or rocky reefs. These animals are used to navigating among crevices, caves and overhangs. Some of these sharks (e.g., epaulette sharks, Hemiscyllium spp.) even exhibit specialized modes of locomotion that enable them to better move about within tight spaces. Many of these sharks also spend a considerable amount of time resting in reef crevices, especially during the day.
It should not be surprising that these reef-dwelling sharks are more comfortable in the limited confines of an aquarium than other sharks. The more active species (e.g., smoothhound sharks, genus Mustelus) that spend more of their time swimming need a lot of room to move about. Although some of these sharks will occasionally rest on the sea floor, they spend more time swimming in the water column.
Bigger is always better when selecting a tank for your shark. Specifically, you should choose one with a larger footprint: more length and width rather than height for the same volume of water. Sharks will utilize the added surface area. In the cases of the sharks I will suggest, keep a tank of at least 180 gallons for an adult specimen; a larger aquarium would even be better (e.g., 300 gallons).
This doesn't mean that juveniles cannot be kept in smaller tanks. They can, but be prepared to step up to a larger aquarium as the shark grows. If you do not have the money or space to keep an adult of the species in which you are interested, don't buy a juvenile. Even if there's a public aquarium in your area, it's highly unlikely they will want to take your overgrown pet, and it is ecologically irresponsible to release a captive shark back into the ocean.
Because room to move is imperative, even for the more sedentary species listed later, keep tank decor to a minimum. Although the species recommended live in habitats that are more structurally complex, in an aquarium, you will want to provide plenty of room so they can move about, usually at night. When they hunt or attempt to create or tuck into hiding places, they may knock aquarium decor loose and dig under rocks and corals.
Place aquarium decor directly on the aquarium bottom before adding sand to the tank so that these items are less likely to crush a digging shark. To create more stable caves and crevices, use adhesives that are available for creating interesting topographical features or to attach corals to a reef. Provide your shark with a suitable hiding place, such as a cave created in a patch reef placed at one end of the tank. By placing the shelter site there, you will leave plenty of open aquarium bottom for the shark to move around. (For more detailed information on setting up and maintaining an aquarium for sharks, you may want to check out my book Aquarium Sharks and Rays ).
Now let's take a look at some of the most suitable aquarium sharks.
Sharks That Walk?
A couple of years ago, ichthyologist Dr. Gerry Allen discovered two new species of sharks in the genus Hemiscyllium (family Hemiscylliidae) that were dubbed "walking sharks” by the popular press because these fish move over the substrate by "walking” on their muscular pectoral and pelvic fins. Although the media believed these sharks were new to science, the first of the walking sharks, known to experts as epaulette sharks, was described in 1788.
Epaulette sharks are truly marvelous. They live on coral reefs around the coasts of Australia, New Guinea and Indonesia. There are seven described species, two of which were recently described in 2008 and at least two species that have yet to be scientifically described. All of the epaulette sharks have very limited distributions. The range of some species (e.g., the common Hemiscyllium ocellatum) has been erroneously extended, due to misidentification of similar sharks in the same genus.
Most of these sharks hide in crevices during the day and leave the safety of the reef at night to feed at adjacent sand flats, rubble beds or sea grass meadows. They use their sensitive sense of smell and electroreceptors to find invertebrates and small, slumbering fish.
Epaulettes have to be the best of the aquarium shark species. Most are small (with maximum lengths under 30 inches) and are handsomely marked. Also, they readily acclimate to tight spaces. As egglayers, they deposit a leathery egg capsule on the sea floor and regularly reproduce in larger aquariums. Only one species, the epaulette shark (H. ocellatum), is currently available in the aquarium trade. I believe this may change soon, as new collecting stations are beginning to open up in West Papua and Papua New Guinea. The reefs in these areas are home to more epaulette shark species than any other region. If enough adults enter the trade, captive-breeding programs could also help provide specimens to hemiscylliid-loving aquarists.
One only has to consider the common name — wobbegong — of the members of the family Orectolobidae to know that these fish are truly unique. The name originates with the Australian Aborigines, which is appropriate, given that seven of the eight described species are most abundant or only occur around Australia. (There appears to be a couple of undescribed species that occur on reefs of Indonesia and the Philippines that have long been misidentified as one of the described Orectolobus species.)
When it comes to their way of life, wobbegongs are the elasmobranch equivalent of a scorpionfish or frogfish. As with these bony fish, wobbegongs are highly sedentary, typically resting in the same spot on the reef for extended periods of time — as long as food supplies are readily available. They rely on being secretive to go undetected by passing prey items, which can include octopuses, crustaceans, smaller sharks, rays and a wide variety of bony fishes. When an unsuspecting prey item moves too close, the patient predator ambushes it.
These sharks are eating machines. Remember this if you are considering putting other fish in with a wobbegong. I once sold a 28-inch wobbegong to an aquarist who told me he was going to keep it in its own tank after I warned him of the wobby's propensity to consume aquarium neighbors. Several weeks later, he brought the wobbegong back. It turned out that he did not heed my warnings about its voraciousness and had placed it in a tank of larger fish. It ate his yellow tang, an angelfish and a large zebra moray, which it regurgitated in a partially digested state. (If a wobbegong eats something that is too large, it will not be able to digest it rapidly enough, in which case it may end up vomiting.)
Another too-large food item that wobbegongs will try to eat are slimmer shark species. I have seen cases in which the prey shark was too long to completely ingest, but that did not stop the wobbegong. It swallowed as much of the thinner shark as possible and lay there with the tail of its victim protruding from its mouth. They will even try to eat smaller wobbegongs (although they can be kept together if they are approximately the same size). You have been warned!
There are only three species in this family that are small enough to be kept in a tank of 180 to 300 gallons. These are Cobbler's wobbegong (Sutorectus tentaculatus), the dwarf ornate wobbegong (Orectolobus ornatus, not to be mistaken for the much larger ornate wobbegong, O. halei), and Ward's wobbegong (O. wardi). All of these species max out at around 3 feet, and because of their normally sedentary habits, are ideal for a larger home aquarium. My favorite of the wobbie clan is the tasseled wobbegong (Eucrossorhinus dasypogon). This species gets larger, needing a tank of 400 to 600 gallons, but it is also the most interesting — it uses its tail as a lure to attract potential prey.
The family Scyliorhinidae is large, with more than 100 species, and includes some of the most attractive of all the sharks. Unfortunately, relatively few Scyliorhinidae sharks make it into the aquarium trade. The coral catshark (Atelomycterus marmoratus) is the one that aquarists will most likely encounter. Note that there may actually be more than one species coming into the aquarium trade that are often mistaken for A. marmoratus.
The coral catshark (Atelomycterus marmoratus) is a small, nocturnal species that is ideally suited for the home aquarium. Photo by Scott. W. Michael
The coral catshark is a reef dweller that tucks itself under debris or within interstices during the day, and comes out to hunt invertebrates and small fish at night. When it hatches from its purselike egg case, it's only 4 inches long, but it can reach a maximum length of about 27 inches.
The coral catshark is a great aquarium species that will do well if provided with hiding places and plenty of surface area to move about at night. These catsharks may look rather benign, but they are efficient predators that will eat any fish or crustacean they can swallow whole.
There are some very attractive cool-water catsharks that are also available on occasion. For example, members of the genus Asymbolus are sometimes exported from western Australia. These sharks mature at a small size (around 20 inches) and would be ideal for captive-breeding programs.
There is also a small Japanese species called the cloudy catshark (Scyliorhinus torazame) that enters the aquarium trade on occasion. These rocky reef-dwelling sharks can be kept in a home aquarium if the tank is equipped with an efficient chiller; water temperature should be 60 to 68 degrees Fahrenheit.
Aquarists in Europe might also have access to the smallspotted catshark (Scyliorhinus canicula). This is a temperate water species that has readily bred in public aquariums. It reaches a maximum length of 24 inches (those species from the Mediterranean) to 3 feet (those from around the British Isles) and is sexually mature at around 17 inches.
Even the smaller species of sharks are not suitable for every home aquarium. The tank needs to be large and aquascaped specifically to house a shark. The potential shark-keeper should also put a lot of thought into the species that he or she wants to acquire.
The best aquarium sharks are not that active during the day. Do not expect them to cruise about the aquarium looking menacing! Please stay away from those species that get too large (e.g., nurse shark) or that are too active (e.g., smoothhounds), and limit yourself to the species discussed here. If you follow this advice, you will be able to keep your shark for decades!
(This article originally appeared in the October 2008 issue of Aquarium Fish International)