Ask the WWM Crew
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Of all the frauds and heartache foisted on unwitting marine aquarium hobbyists, cool to coldwater organisms offered as tropicals has got to be amongst the worst. Where it comes to these animals being the cartilaginous fishes called sharks, maybe it is the zenith of bad. Folks go to expensive and inordinate ends to secure large quarters, over-sized filtration and the money to purchase specimens to find they too-often die mysteriously, jump-out, or live greatly foreshortened lives. All unnecessarily.
Here it is my intent to reveal these fishes as what they really are; poor choices for tropical settings of any kind, and organisms requiring hundreds to thousands of gallons of room, adequate circulation, aeration and filtration to be kept happy and healthy.
Cool to Coldwater Shark Species:
Here we're referring to sharks that are collected in below room temperature water. This is one of the areas I diverge from most other shark-aquarium writers. Unless you're committed to providing a very large system with adequate cooling, please shy away from the following animals. Though often offered, cool water sharks generally fare poorly. Who are they? Many more species than you may be aware of are collected from cool/cold water and offered as tropicals... see below.
Hornsharks (with two dorsal spines), aka Pig, Bullhead, Port Jackson's, family Heterodontidae. Cool to semi to sub-tropical members of the family Heterodontidae. Most often you'll find the Californian H. francisci and southern Australian H. portusjacksoni. For aquarium use look for the more tropical and gorgeous Heterodontus zebra. One genus, eight species.
Family Scyliorhinidae, true Catsharks, Swell Sharks. With fifteen genera and some 89 described species, you'll have to check to make sure the one's you're looking at are tropical and stay small enough.
Smoothhounds, Dogfish family Squalidae: Two genera, eleven species. The Spiny or Piked Dogfish, Squalus acanthias is the most commonly dissected fish for H.S. and College anatomy classes and the most often member of the family seen offered to aquarium hobbyists.
Houndsharks, family Triakidae: eastern, western Atlantic, Indian and Pacific Oceans. Nine genera, 39 species. Some are cold, other warm water species. Of the genus Mustelus, most often seen by hobbyists are M. californicus (the Gray Smoothhound) and M. henlei (the Brown Smoothhound); both cool to coldwater animals. Both to more than three feet in length.
Habitat & Display
First of all the obvious, the bigger the tank, the better; with a beefy, high flow rate (two plus turns per hour) filtration system. Less "show tank" shape and more flat and shallow; ideally with rounded (mega-hex?) corners, otherwise minimized physical barriers to swimming around. Optimize surface area. Again, LARGE is a key word here. These are active animals that require space to move, turn about. Conceal tubes, heaters, airlifts, filters, to prevent run ins, pull ups, tunneling, breakage... Sharks of all kinds at times display occasional great bursts of energy, speeding about, crashing into things.
About substrate; finer, less angular gravels are preferred to avoid scraping. Dolomite, marble are out; fine, crushed coral sand is ideal. If you must have other decor, restrict it to some central area to keep the swimming perimeter clear. Be aware that cool to tropical water sharks are diggers and will undermine your artistic edifices; build accordingly.
A mention of the likely number two cause of death of these species: leaping out of the water. Make sure to have a secure, heavy or latched cover to keep your shark/s in the tank, and off the floor.
Temperature is key here for a two key reasons. Cooler water holds more dissolved gas, and in the opposite direction depresses metabolism and motion... both "good things" for large animals in small water volumes. If you want to keep these species healthy, for anywhere near a natural lifespan you will need a water chilling mechanism.
Salinity should be kept high, near worldwide sea level, @ 1.025 specific gravity, and constant. Reason? Sharks (actually all cartilaginous fishes), unlike bony fishes are semi-isotonic (equal in concentration) with the percentage of certain charged materials (like salts) in their general environment. To some degree they manipulate nitrogenous waste metabolism and excretion with the make-up of the surrounding water... you get the point. Large, regular water changes of the same specified specific gravity will get you by.
Monitoring water quality and avoiding metabolic waste bottle-necking should be paramount. Sharks are large, metabolically active animals. How many pounds/kilograms, make that ounces/grams of fishes do you maintain now? Humbling, isn't it? Check out the smallest sharks available; one most likely weighs in at more than all the fishes you've ever kept total. The need for good circulation, regular maintenance, over-engineered and built filtration is clear.
About metal of any sort in the system: to be avoided at all costs. Ferrous (iron bearing) matter is especially problematical. Sharks possess an acute electromagnetic sense associated with pit organs located beneath their heads (the ampullae of Lorenzini). Other metals in solution cause sharks to go anosmotically off-feed. Remove metal, even plastic or glass-encased from the system and sump, out of harm's way and to reduce affecting your shark. Even metal rebar (reinforcing steel) cast into concrete walls in public aquariums has been indicted as "driving these fishes crazy", resulting in their deaths.
My usual endorsement for marine systems cannot be more emphatically re-stated here: I would not have a marine system without a functioning protein skimmer. With such large animals as sharks, processing so much proteinaceous material (food), a foam fractionator is an absolute necessity in a closed system. Enough said, or written, I trust.
As regards standard formats for metabolite conversion, the most efficient fluidized bed, and wet-dry technologies are favored, with rapid sand and more conventional large canister filtration being just barely adequate. undergravel filtering is not endorsed at all; the metabolically active surface area is too small to be practical and too easily disrupted.
Though known to chomp on their own or other shark species in a feeding frenzy, most accounts show captive sharks steady eaters of the foods they've been trained on and not each other unless hungry and/or of a great size difference.
For hobbyists, there are exceedingly few systems that are large enough to consider having more than one shark specimen. Sharks will try to eat any invertebrate even Sea Cucumbers, Bivalve Mollusks, Hermit Crabs, shell and all. I have dissected dozens of large sharks for science and education, finding cans, rocks, bicycle parts, jewelry, etc. in them.
Is simple enough. You are encouraged to place your shark only in a "seasoned", read that as "old" system. One that has been time tested with another fish. Do be present during the entire operation, do add aeration, increased circulation in the shipping container... if the animal is large directing water flow into the sharks mouth.
Most sharks are fine with other species providing they are not mouth-size or slow-moving. Surprisingly, rather than the perpetrator, your shark may be the victim of harassment by its tankmates. Large angelfishes, triggers, puffers, et al. are recorded as opportunistic shark pickers. Large Moray Eels may eat much smaller shark tankmates.
Reproduction, Sexual Differentiation/Growing Your Own:
Sharks have an astounding reproductive biology. Different species lay eggs, give birth live with and without umbilical-like attachments; with surprisingly long gestation periods and low birth rates. If you're going to invest the money to try one out, put in the time to investigate the way the sharks make their life.
All utilize sex, that is internal fertilization, granting an easy manner of determining whether you are looking at a male or female. Males possess claspers, specialized tube-shaped pelvic fins for genetic transmission. The pelvics of females are more triangular shaped.
Locomotion and It's Importance in Practical Husbandry:
Sharks move about and aid their blood circulations by throwing their bodies into sinusoidal curves. They lack swim bladders, but to some degree compensate for the lack of a gaseous hydrostatic mechanism by their possession of relatively large, fatty livers (which float). Most sharks also utilize hydrostatic lift, capitalizing on having more surface area on their upper bodies than lower, staying in constant motion. The induced drag results in a "lift". Tail (heterocercal, with a larger upper lobe), pectoral fin shape also add lift.
The practical implications of their mode of transport is that sharks need lots of room, can't change direction or level easily, and hate square system corners.
Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes
Captive sharks in good health will feed on a wide variety of meaty items, including most tankmates. In the wild the species above consume mainly crustaceans, small fishes and various types of worms; but in captivity they can be trained to take cut fish or other meaty invertebrate foods.
Don't overfeed! Offering food two, three times per week is adequate. Sharks are known to eat infrequently in the wild. This warning against overfeeding can't be stated strongly enough. Too much, too often leads directly to two bad situations; poor water quality and a rapidly growing, large specimen.
Don't hand feed! Besides the obvious and very real danger of a nasty laceration from biting, there is an increased risk of introducing pollution. Instead, train your shark to "stick" feed with the food skewered on a plastic rod. Keep your hands out of the tank as much as possible.
Disease: Infectious, Parasitic, Nutritional, Genetic, Social
Sharks do very poorly if and when treated with many standard remedies. Copper compounds are deadly as are many dye solution treatments. I likewise strongly differ with some authors who endorse the use of organophosphate pesticides. Please see my self-cited piece on DTHP use. This bug-spray ingredient is common in several preparations worldwide under various names (Masoten, Dylox, Neguvon, among others).
Reddening due to irritation and possible Vibrio bacteria may be treated with Chloramphenicol (if you can still get it) or tetracycline administered internally via a food bolus.
I'm rather hesitant to mention freshwater and formalin baths for blatant external parasite extermination. Often the damage to the shark (and you!) from thrashing about is greater than any good the dip might do. Be careful, and follow the above recommendations in handling.
Sharks and their relatives are host to many worm, crustacean and protozoan parasites. The best way to avoid problems with them is to do your best to purchase a clean, healthy specimen, give it good care, and prevent introducing these parasites. The last is best accomplished by not using live or fresh seafoods; use frozen or freshwater instead.
Colored Anemones, more recently even dyed stony corals, injected Glassfish (family Ambassidae)... the list of scam livestock continues and evolves seemingly without end. Don't be misled to believe keeping any species of marine shark as being easy... particularly ones that live in temperate waters. They may "last" for a short while (the above pictured species have been known to live more than twenty years in captivity), but not happily. Unless you have a huge system, with a mechanism for ensuring consistent and optimized cool to coldwater conditions, leave them in the sea where they belong.
If you must try a tropical shark species, look to the Bamboo and Epaulette Sharks, these stay relatively small and are behaviorally and metabolically less active than other common shark species that are often on offer (e.g. Nurse Sharks, Wobbegongs).
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