From the ferocious great white shark (Carcharodon carcharias) to the graceful white-spotted eagle ray (Aetobatus narinari), Elasmobranchii are a diverse group of boneless fishes that are circumglobal, inhabiting a diverse array of habitats, temperature ranges, salinity, and niches in the world’s oceans and rivers.
It is no wonder that these unique creatures, while usually boasting relatively bland coloration compared to the typical teleostei reef fishes, pique the interest of pretty much every hobbyist. This group of fishes definitely has its challenges but, with proper information and species selection, can be kept fairly easily by a moderately skilled aquarist with a generous budget.
The space-swim pattern continuum
As with every other family of fishes, sharks have a wide range of spacial considerations by species. “Go big or go home” is a decent motto for most species. Length, width, and shape are the most important factors with all elasmobranchs, with depth being a factor only for pelagic shark species.
Most hobbyists are intrigued by pelagic (open-ocean) sharks like blacktip reef sharks (Carcharhinus melanopterus) or bonnethead sharks (Sphyrna tiburo), but a typical tank will not suffice for these obligate swimmers. They prefer a kidney-bean-, figure-eight-, or at least cylinder-shaped pool or tank to do well. These sharks need large straight-aways and long corners for energy conservation.
Pelagic sharks put in boxy or undersized aquariums tend to expend more energy than they can consume and eventually perish. I recommend at least 8,000 gallons to keep even the smallest pelagic shark species, but most pelagic sharks should be left to public aquarists. I will also mention smoothhounds (Mustelus spp.) here as they are somewhat active yet are buccal-pumping versus ram-ventilating sharks. They still need a system that is several thousand gallons to thrive due to their active nature, but shape is of lesser concern.
Usually, aquarists settle for the benthic (bottom-dwelling) sharks such as members of the family Hemiscylliidae, which include the bamboo (Chiloscyllium spp.) and epaulette sharks (Hemiscyllium spp.). These sharks can do well in decently sized aquariums—around 250 gallons—with length and width being more important than height. Don’t be fooled by their lethargic nature by day; these animals are extremely active at night!
Other notable species are the coral cat sharks (Atelomycterus spp.). These are probably the smallest shark species that are readily available to hobbyists and do extremely well in tanks with a decent amount of secured rockwork in your typical reef aquarium. An aquarium of 200 gallons would be the minimum for these species.
Horn shark species in the family Heterodontidae have similar requirements as other benthic sharks. They aren’t especially active but need some space due to their eventual size at around 4 feet in length. I would recommend a minimum of 1,000 gallons of cool water for this family long term, with length and width being more important than depth.
Rarely, you may find a nurse shark at your local fish store. Nurse sharks (Ginglymostoma spp.) get extremely large, eat a ton of food, and need a large pool or tank of 5,000 gallons minimum with a state-of-the-art filtration system to compensate for the bioload that they produce (filtration will be covered in part 2—diet and water quality). Their cousin the short-tail nurse shark (Pseudoginglymostoma brevicaudatum) stays much smaller but is much more rare in the trade. I am also going to mention here the beautiful zebra shark (Stegostoma fasciatum), as it is similar in its habits and requirements. These species are not for the light-walleted.
Wobbegongs (Orectolobus spp.) are also available at times and should be kept with caution. They eat anything that fits in their large mouth but generally stay put, waiting in ambush, so they do not need as much space as their length would indicate. A tank that is two and a half times the maximum length of the wobbegong and one and a half times in width should suffice.
Rays and skates
Most rays that you see available at your fish store are benthic and tend to hang on the bottom most of their day. However, even benthic rays need quite a bit of free swimming room when they do get moving. A bottom full of obstructions does not mix well with most rays available.
A fine grade of sand and a low amount of live rock are key to stingray survival in home aquaria. Fiddler (Trygonorrhina spp.), Cortez (Urolophus maculatus), round (Urolophus halleri), yellow (Urobatis jamaicensis), and blue-spotted ribbontail rays (Taeniura lymma) are frequently sold in stores. These animals need at least a 6-foot x 4-foot space that is free of obstructions to roam when nearing adulthood. Sometimes larger species, like southern stingrays (Dasyatis americana) and reticulated whiptail rays (Himantura spp.), make their way into the hobby; avoid these species unless you have a system that can handle a 200-pound fish.
Every once in a while you will see a batoid such as a cownose (Rhinoptera bonasus) or Californian bat ray (Myliobatis californica) for sale at a store. These animals need extra space as they are pelagic and swim constantly. I would suggest a 15-foot-diameter system at the minimum for these species, but it does not need to be deep. Most of these are schooling animals, so several animals would be preferred.
Skates of the family Rajidae are rarely available to the average hobbyist, but space consideration is similar to that for benthic rays. They usually stay under 2 feet in disk size and have some interesting behaviors. A 6-foot x 4-foot space with some fine sand to bury in would be adequate.
Special accommodations required
Elasmobranchs are definitely not for the average aquarist, but with a large system, they can do quite well in captivity. If given the proper space, they are able to carry on normal behaviors that are important for shark and ray health and energy conservation. Space is merely scratching the surface of modern elasmobranch husbandry, but it’s one of the most critical components of keeping them successfully.
See Part 2 of the Elasmobranch Enthusiasts series on diet and proper nutrition, Part 3 on filtration, and Part 4 on reproduction.
Photo credit: Paul Poeschl