How it works: Feeding the fish, and keeping them healthy
It’s easy to wander into an aquarium and “ooh” and “aah” over the boundless schools of fish that greet you from every tank.
But once the crowds have gone home, those fish are still there, alive, thriving … and really hungry.
How hungry? Well, just one example: At the Tennessee Aquarium, home to 12,000 different animals from fish to reptiles to amphibians and more, the annual food budget tops $165,000.
That’s in the estimation of Thom Demas, the facility’s curator of fisheries, whom we reached last month for an interview.
So how much frozen fish and other foodstuffs does $165,000 get you? Demas points to the facility’s largest marine tank, which aims to be a snapshot of the Flower Garden Banks National Marine Sanctuary in the Gulf of Mexico.
“In that tank, we average about 300 lbs of food a week, plus an additional amount of food for the large sharks, which is probably another 40 lbs,” Demas said.
And it’s not like you can just toss in some flakes and pellets and leave the ravenous marine life to tuck in. Aside from research into species’ preferred diet, staff can examine individual species’ morphology – for example, if their mouth is located low down like a ray or a sturgeon, they will tend toward food species that are bottom dwellers – to put together a menu.
Aquarium staff will try to get food similar to what a species would eat normally, but the most important thing for the fish, Demas said, is a varied diet. Some species, like sharks and sting rays, even get a little extra, in the form of custom-made vitamin supplements.
“Putting together a feeding plan, a nutrition profile for these animals is something that isn’t taken lightly, and a lot of time and effort goes into it,” he said.
If you’re wondering, food stock comes from the same vendors that supply seafood restaurants – trucked in sometimes from hours away, but frozen to preserve freshness.
“We always try to make sure we’re buying from vendors that are acquiring their seafood in a sustainable fashion, that’s very important to us,” Demas says.
“We make sure it looks good, looks fresh, we thaw it, make sure the eyes, or the whole fish are not clouded. Basic check you do, just like you would if you were purchasing food for a restaurant or any situation,” Demas said.
How to train a shark to not eat everything that moves
But always literally hovering in the background are the sharks – often kept in the same tank as smaller fish that could easily become a mouthful for a peckish predator.
You can’t always stop nature, Demas says, but you can condition a shark to live in an aquarium environment without viewing its tank mates as a handy buffet – that means no live feedings.
“Obviously sharks are top of the line predators. Do we feed them live fish? Absolutely not. Number one reason for doing that in my mind is, if you bring a live fish in, I’ve got to quarantine that animal, and I’m still running the risk of introducing a disease into that exhibit, when I put that live fish in there.”
Instead, through acclimatization and conditioning, the shark can learn to be satisfied with a mackerel on a pole.
But even still, aquarium staff know they are dealing with a predator, and have to keep the beast’s feeding schedule to an exact science. They learn the habits of each individual, make sure it’s fed 2-3 per cent of its body weight, three times a week.
It seems to work, for the most part. Demas says the six larger sharks at the Tennessee Aquarium might devour a grand total of one of their tank mates a month, if that.
“It’s about making sure they’re satiated to the point it’s not worth hunting, but we don’t want the to get overweight, because like with people, you eat too much, you get obese, you get circulatory issues you’ve got blood issues, all kinds of problems. And then if I put my sharks on a diet, they are going to want to eat everything.”
Paula Romagosa, curator of the Shaw Ocean Discovery Centre in Sidney, British Columbia, adds that the risk can be minimized by putting the sharks in with animals they are not known to prey on in the wild.
"And also by keeping them well fed. If you keep them well fed and well enriched, usually they won’t eat each other, but there’s always the risk that someone will eat someone else,” she says.
Stave off disease
That vigilance serves another purpose: Heading off disease before it becomes a serious problem.
Having the food arrive frozen kills any parasites that may be found in the feedstock, but it’s still possible some diseases might slip through, that might not be an issue in the open sea.
“Because we know there are certain diseases, common diseases, in nature, they’re just there, they don’t really bother the fish. But if you have them in a smaller system with a smaller volume of water- I don’t care how big your fish tank is, it doesn’t replicate the ocean in terms of volume – the parasites have the advantage.”
“So our goal is, even if we don’t see a disease process on the fish, to make sure these common things don’t slip through.”
Arrivals to the aquarium are put through a minimum 30-day quarantine, undergoing regular monitoring of their appearance and diet.
If staff see a sore or clouded eyes or other signs of ailment, they call in their vet to care for the animal – injecting with antibiotics or other medicine if necessary.
“The assessment is really a daily effort,” Demas says. “We do not, however, catch them up just to check them. We … allow them to live a normal life, then observation, clean exhibits and good nutrition.”
If serious enough, a diseased fish will be quarantined off-site until it is well enough to be returned to the tank.
But disease will happen – although fortunately, such outbreaks as there are have never been severe enough at the Tennessee Aquarium that a full or partial cull has been necessary.
What staff can do, Demas says, is prepare the exhibit, tank and even the water to minimize the risk of contamination in the first place.
Ozone is a useful tool – like bleaching a bathroom wall, injecting ozone into the water while it is being treated kills off all bacteria before the water is returned to an exhibit.
Then there’s every day little things to do, Demas add, like regular vacuuming of a tank, and constant monitoring of fish for erratic behaviour or visible symptoms.
“To think that any exhibit anywhere has no disease in it would be like saying people don’t have bacteria on their body. Of course they do. So it’s about good housekeeping and paying good attention,” he said.
At the Shaw Ocean Discovery Centre, Romagosa says aside from ozone, water drawn directly from the sea is put through a series of filters than can screen particles and contaminants down to 35 microns.
But, as in Tennessee, sometimes things get through, the most recent example being sea star wasting syndrome, which afflicts sea stars from California to Alaska.
Romagosa says they have had to treat and, unfortunately, euthanize one sea star that contracted the disease, but for the most part, quarantining and treatment in separate tanks is the way to go.
“We can try separate animals that show any signs of disease and quarantine them and treat them separately from the collection,” she says.
HOW IT WORKS: Check back tomorrow for the Top Ten Aquariums, and on Sunday for our feature on the world's weirdest sharks.