The Rhino with Glue-On Shoes (26 page)

Water-Breathing Dragons

by Ilze Berzins, PhD, DVM

A
lex walked into my office with a frown on his face. “Dr. Berzins, we're in trouble. The dragons are floating.”

“What do you mean?!” I asked, trying not to panic. These are not words you want to hear about any new fish shipment, especially when the transport box contains a pair of rare weedy sea dragons, the first to arrive at your aquarium.

“They're at the surface and can't seem to dive down.”

A sea dragon is not, as the name suggests, the size of the Loch Ness Monster. It is a delicate, unusual-looking, and endangered fish from Australia, related to the sea horse, the tiny S-shaped fish you can buy almost anywhere. Dragons have elaborate leafy appendages, like fronds of seaweed, attached to their colorful bodies. At most, a full-grown weedy sea dragon reaches eighteen inches in length and weighs less than three ounces.

Everyone on staff at the Florida Aquarium had been excited about the arrival of these special fish. In one way or another, we'd all helped in the planning, which had taken over a year, starting in the spring of 1998.As the aquarium's head of veterinary services, I'd been involved in every step of the preparations. Our biologists had researched ideal water conditions, housing, and what to feed the fish. Using this information, our exhibit designers had custom-built a new tank, one that would also provide a great view of the dragons for aquarium guests. Our marketing and public relations people had taken it from there, naming the new exhibit Dragons Down Under. I'd talked to a number of other fish vets about dragon medicine, just in case something went wrong.

The dragons had arrived at the aquarium that morning via special air cargo from Melbourne, Australia, with a stopover in Los Angeles. We'd planned that the fish would stay in a special holding tank for a minimum thirty-day quarantine. This would give them time to recover from the stress of transport. We'd also check them for parasites, deworm them if necessary, and keep a close eye on their feeding behavior. Next we'd move them to the new exhibit if they were healthy.

Given their long plane flight and the two days they'd spent in a dark, sealed bag, I fully expected to find one or both of the dragons acting sluggish or looking thin. These are common signs of mild stress due to shipping, since fish are not fed during transport and are in a confined space.

At worst, if the concentration of dissolved oxygen in the water had dropped more than it should have, or if a considerable level of nitrogen (the waste product of fish) had accumulated, I wouldn't have been surprised if the dragons had a high gilling rate. This sign of stress is equivalent to breathing fast. By rapidly opening and closing their gills, which are supplied by a dense network of capillaries, fish can take in more oxygen and also get rid of waste products that build up in the bloodstream.

Alex, one of our biologists, held the lid of the box open while I took my first look at the dragons. Just as he'd warned, they were floating at the surface and struggling to stay upright. I watched them for several minutes, thinking about what to do next. For whatever reason, they couldn't keep their bodies beneath the water's surface. This species of sea dragon has a long snout, and the gills sit right behind the angle of the jaw. Neither of the new dragons could keep its snout or gills under the water. They were piping, or gasping—not for air, but for water. This was a life-threatening situation. No vertebrate animal can survive without oxygen. Something must have gone wrong during the shipment, or perhaps the box hadn't been properly prepared to begin with.

I quickly directed Alex to take a sample of the shipment water to the water quality lab. He'd been instrumental in helping me get the animals to Florida, following up on every detail to make certain everything went smoothly. He looked just as worried about the dragons as I was. We tested for temperature, nitrogen waste product levels such as ammonia and nitrite, dissolved oxygen saturation, salinity, and pH. The results were normal.

If the problem wasn't in the water, it had to be inside the patients. Dragons, like many other types of fish, have air bladders (also called gas or swim bladders). This organ helps them with buoyancy control, so that they can maintain their position in the water. Maybe their air bladders had become overinflated during transport. Even worse, they might have ruptured, allowing free air into their body cavities. This excess air, whether inside the bladder or outside, would make it impossible for the fish to swim beneath the surface of the water.

I ran through the possible reasons for an overinflated air bladder. Changes in air pressure during the flight could cause this; maybe the cargo hold hadn't been properly pressurized. The lower pressure could result in gas leaving the bloodstream and forming gas bubbles in the tissues of the fish. Another possibility was that the box had been exposed to excessively low temperatures, which could have affected the concentration of oxygen and other gases in the water and bloodstream, increasing the amount of gas released into the air bladder, and then expanding when temperatures warmed up again. Or, and this last possibility was at the top of my rule-out list, the water in the sealed transport bag had been supersaturated with oxygen gas during some part of their trip.

If you've ever purchased a pet fish for your home aquarium, you may have seen the salesperson tie the plastic bag so that it puffs out with air, like a half-filled water balloon. The oxygen in the air will help keep the oxygen levels in the water at a healthy level. When fish are transported long distances, pressurized oxygen gas is added to the container to ensure that oxygen levels remain high inside the bag for several days. But if the dragons' sealed bag was inadvertently overpressurized, the gas pressure inside the air space, and thus the water, would have been initially too high, exposing the dragons to excessive, harmful gas pressures.

It was going to be difficult, if not impossible, to find out for certain what had happened to the dragons during transport, and it wouldn't necessarily change the treatment options. Time was of the essence. My priority was to confirm the diagnosis even if I couldn't be certain of the root cause. The game plan was simple: radiograph the animals to look for overinflated air bladders.

Since the dragons were small and relatively inactive, they didn't need anesthesia for radiography. We could position them on the X-ray film cassettes the way we do other small fish, take the picture quickly, and replace them in the water. Gently I picked up the first patient, wearing powderless latex gloves to minimize damage to its skin and protective mucus, and placed it on its side directly onto the cassette. Susan, my veterinary technician, positioned the X-ray beam, lined everything up, and set the machine. She got ready to hit the exposure button while I darted behind the lead screen. Seconds later, I ran back into the room to return the dragon to the water. We repeated the procedure for our second patient.

After developing the film, we could see that the body cavity of one dragon was completely filled with air. In the other, we saw the outline of an overinflated air bladder, which was most likely compressing the intestines directly below the bladder.

There might appear to be a simple solution to this life-threatening problem: place a needle into the air bladder and withdraw the excess air. But in a sea dragon, such a procedure can result in the introduction of infections or in laceration of other internal organs. To complicate matters further, the dragons' thick scales, like a coat of bony armor, make it difficult to insert a needle through the skin without squashing the fish.

I had another idea: treat the fish as you would a human. Put them in a high-pressure chamber that gradually moves the trapped gas out of the wrong places. Maybe we could take them to a dive chamber and treat them as if they had the bends, a common complication of scuba diving. Florida is a popular diving destination, and I knew there were several recompression chambers nearby.

This thinking was based on what we know about fish anatomy. The air bladder is normally filled with various gases, oxygen being one of them, thanks to a system known as countercurrent exchange. The oxygen gets there via a complex bed of arterial and venous capillaries known as the rete mirabile (Latin for “wonderful net”). The capillaries are arranged in such a manner that blood rich in oxygen flows past blood low in oxygen; the gas then moves from areas of high to low concentration. The exchange takes place near the wall of the air bladder, so it can deflate or inflate depending on the concentration of the gases passing by in the blood vessels. By exposing the dragons to high pressure, simulating a dive, maybe we could drive the gas back out of the bladder and into the bloodstream.

Fish also use countercurrent exchange to breathe. The arrangement of capillaries in the gills is not as elaborate as in the swim bladder rete, but the overall result is the same. The gas moves from high to low concentration, from the water into the bloodstream and then to the tissues. This is, of course, why our floating dragons were in big trouble. Their overinflated air bladders prevented them from keeping their gills underwater. If we could get the gas out of the air bladder and into the bloodstream, maybe it could leave via the gills.

Though we humans don't have an air bladder, the gases in our bloodstream are subject to the same rules of physics. They move in and out according to pressure as well as chemical differences. The bends, also known as decompression sickness, occurs when scuba divers ascend too quickly. The air in their tanks has been compressed under pressure, ensuring that oxygen is delivered to the tissue as they dive down. As long as the diver ascends slowly, these gases will leave the body as the pressure equalizes. However, if the diver rises to the surface too fast, the gases will expand and form bubbles in blood vessels and tissues, which can cause painful tissue damage or even death. Trapped gas in the wrong place is a medical emergency—in any species.

I decided to go for it. It sounded like a weird plan, taking tiny fish that look like seaweed into a hospital recompression chamber, but why not give it a try? I knew that our local hospital, St. Joseph's, had such a chamber. In addition to treating dive accidents, it's used in the treatment of several human diseases, including diabetes. People with this disease have very poor circulation in their feet and hands, and the increased chamber pressure helps improve oxygenation.

For people with the bends, the chamber pressure forces gas bubbles in the tissues to dissolve and go back into the bloodstream, where the gas would then be slowly released out through the lungs. In the case of the sea dragons, I hoped for the same thing: the pressure would compress the excess gas out of the air bladder and allow it to be absorbed back into the bloodstream, and out of the body through the gills.

When I called the hospital, the officials responded to my odd request by giving us an appointment for the next morning. Because running the chamber is time-consuming and expensive, they requested that the dragons share the chamber with several human patients. Grateful for the offer, and knowing the dragons couldn't survive for much longer, I accepted.

In order to keep the animals from staying at the surface overnight, we placed them in the container we'd prepared for their arrival. Using a plastic grate, we gently pushed the dragons down into the water and left the grate in place so that they would remain several inches under the surface.

The next morning, Alex filled a portable acrylic tank with about twenty gallons of water and set it in a shallow Styrofoam container to which we added ice. We wanted the water temperature in the tank to stay relatively cool, around 60° Fahrenheit. He added an air stone attached to a small portable compressed air tank that would keep the water oxygenated. Carefully I slipped the animals into the tank and, with the help of Alex and three other biologists, slowly lifted the “travel package” into a van.

An entourage of officials and public relations personnel met us at the hospital. Dragon paparazzi!! The local press wanted to film the event because it was so unusual; also because it helped highlight the fact that many of the procedures used in human medicine can be applicable to animals (in fact, many are first developed using animals).

We set the tank and accessories on a cart and wheeled it down the hall to the chamber room. The chamber itself looked like a large steel bank vault, with pressurized windows on the sides, and several chairs. There were lots of curious looks as well as a few chuckles from the hospital staff and the human patients who were waiting for the procedure to start. Maybe the sea creatures would help make a long, boring procedure a bit more exciting for everyone. After the people had taken their places in the chamber, I walked in with the tank that held the dragons and set it near one of the windows so Alex and I could watch the procedure.

The hatch was closed, locked, and sealed to deal with the pressure changes, and the process began. The pressure in the chamber would slowly increase, simulating a sixty-foot dive. The two animals in the acrylic tank gradually began to sink toward the bottom—precisely as we had hoped. There were a few thumbs-up gestures from the patients in the chamber.
Phew,
I thought,
maybe we can save these little guys after all.