Slithering on the bottom

Dear Lisa:

It sounds like your seahorse was suffering from chronic pouch emphysema, which was causing the buildup of gas in its brood pouch. I think you get the right thing by treating your stallion with Diamox to resolve the issue with Gas Bubble Disease, which is a potentially fatal condition.

However, your seahorse is now apparently dealing with negative buoyancy, the tendency to sink, which is a much less serious issue. Many times a problem with negative buoyancy is simply the result of an underinflated gas bladder or swimbladder, as explained in more detail below, Lisa:

As in many other bony fishes, the seahorse’s gas bladder functions as a swim bladder, providing the lift needed to give them neutral buoyancy (Seahorse Anatomy, 2004). In essence, the swim bladder is a gas-filled bag used to regulate buoyancy. Because the seahorse’s armor-plated body is quite heavy, this organ is large in Hippocampus and extends well down into the body cavity along the dorsal boundary (Seahorse Anatomy, 2004). It will have a whitish to silvery appearance and is a simple, single-chambered sac that begins at the bend in the neck and extends to about 1/3 of the length of the coelomic cavity (Bull and Mitchell, 2002).

The gas bladder arises as a simple pouch or outgrowth from the foregut (Evans, 1998). In newborn seahorses, this connection with the gut is retained as an open tube, called the pneumatic duct, and seahorse fry gulp air at the surface to fill their gas bladder initially. There is only a short window of opportunity to do this, since the fry lose this open connection very early in life. As a result, the air bladder is often completely closed off (physoclistous) in fry that are more than a few days old, and they can no longer inflate their gas bladders this way. Consequently, fry that miss this early opportunity to gulp air — perhaps as the result of an oily or greasy film at the surface of the water — suffer from underdeveloped swim bladders. As they grow and become heavier, they sink to the bottom and are unable to swim or feed normally. On the other hand, accidentally ingesting air after the pneumatic duct closes off, or over inflating the swim bladder by gulping too much air while feeding at the top or entrapped by the surface tension, result in fatal buoyancy problems that leave them bobbing helplessly at the surface, again unable to feed.

Past the newborn stage, the seahorse’s swim bladder is completely self-contained, with no duct connecting it to the esophagus. As a result, they can only regulate their buoyancy by resorbing gas from the swim bladder or secreting more gas into the bladder, which is a relatively slow process (Jobling, 1995).

The composition of the gas contained within the swim bladder is about 80% oxygen, with much lesser amounts of carbon dioxide and nitrogen (Evans, 1998). The oxygen that fills the swim bladder is delivered via the bloodstream, but in order to do this, the oxygen must be secreted from the blood to the lumen of the swim bladder against a strong gas pressure gradient, and once deposited therein, the gas must be prevented from diffusing back into the blood (Evans, 1998).

This is accomplished with the aid of the gas gland, a very sophisticated organ located in the wall of the swim bladder, and the rete mirable or “miraculous net,” which delivers blood to the gas gland (Evans, 1998; Jobling, 1995). With the help of the rete mirable, the gas gland is capable of extracting gases from the blood stream and concentrating them into the swim bladder. The rete mirable is basically a dense network of blood vessels running parallel to each other, which function as a countercurrent exchanger. Capillaries carrying oxygen-rich arterial blood from the gills to the gas gland run parallel to and directly alongside capillaries carrying oxygen depleted venous blood from the gland in the opposite direction (Evans, 1998). It is countercurrent exchange in the rete mirable that acts to retain the swim bladder gases. To the naked eye, the rete mirable appears as one or more circular patches of blood vessels on the surface of the swim bladder (Diseases of Ornamental Fish, 2004).

Gasses and solutes in the venous blood leaving the gas gland move into the incoming arterial blood through the rete mirable via passive diffusion and are returned to the gas gland (Evans, 1998). In this way, the rete acts as a trap that retains the gases in the swim bladder.

The respiration of epithelial cells in the gas gland releases lactic acid and CO2, and these substances are then trapped in the rete via countercurrent exchange and returned to the gas gland where they accumulate (Evans, 1998). As a result of this multiplying effect of the rete mirable, conditions within the gas gland can become 10 times more acidic than normal (Evans, 1998). This is important because hemoglobin loses the ability to bind oxygen under acidic conditions, so the oxygen-rich arterial blood flowing into the gas gland releases the oxygen it is carrying in the gland (Evans, 1998). The oxygen that’s offloaded due to the acidification of the blood becomes concentrated in the gas gland until it is finally secreted into the swim bladder itself.

Removing excess gas from the swim bladder is an entirely different matter. The gas gland plays no role in gas resorption, which occurs in an entirely different area of the swim bladder, called the oval (Evans, 1998). The surface of the swim bladder in the oval region is covered with a meshwork of thin blood vessels, which receive a different blood supply altogether than that of the gas gland (Jobling, 1995). It is there, in the oval, that gas resorption occurs. Gas removal takes place only when a fish is rising in the water column and thus experiences reduced hydrostatic pressure. At other times, the blood vessels that supply the oval are closed off by a series of muscular valves; with no significant blood flow to the oval, there can be no gas resorption (Evans, 1998).

Okay, Lisa, that’s a quick rundown on how the seahorse’s gas bladder or swimbladder regulates its buoyancy. The mechanisms described above allow the seahorse to maintain neutral buoyancy, the point at which is weightless in the water, and can therefore maneuver and swim about effortlessly. Many times when a seahorse is experiencing a problem with negative buoyancy, it will be able to resolve the problem itself by secreting more oxygen from the gas gland into the swimbladder. But this is a slow, gradual process that may take several days. As long as the seahorse is still eating and keeping up its strength, you can afford to wait and see if the problem corrects itself. So for the time being, I would recommend doing nothing as long as the seahorse is able to feed normally and keep its strength up. Just take your time and wait to see if your stallion is able to gradually secrete more gas into its swim bladder and counteract the negative buoyancy.

Good luck.

Respectfully,
Pete Giwojna, Ocean Rider Tech Support

Dear Chris:

I’m sorry to hear about the problems you are having with some of your seahorses. It’s very difficult to determine what is going on with your ponies from afar with so little to go on, but the seahorse that is “playing dead” curled up on the bottom and slithering around with labored breathing and no appetite sounds very much like it could be suffering from ammonia poisoning or nitrite toxicity, so I suggest that you check your water quality parameters immediately to see if there has been a spike in the ammonia or nitrate levels.

The most obvious symptoms of ammonia poisoning/nitrite toxicity are a loss of equilibrium, hyperexcitability, increased respiration and oxygen uptake, and increased heart rate. At extreme ammonia levels, fish may experience convulsions, coma, and death. Seahorses exposed to less extreme ammonia levels will struggle to breathe. They will be lethargic and exhibit rapid respiration. They may appear disoriented, periodically detaching from their hitching posts only to sink to the bottom.

In significant cases, you will often see the affected seahorses lying prone on the bottom unable to right themselves at all for extended periods, blindly bumping into objects on the walls of the aquarium in complete disorientation, and going into actual convulsions, accompanied by severe respiratory distress.

Ammonia poisoning is completely reversible providing the seahorses weren’t exposed to toxic levels for too long, and the best first aid you can provide for ammonia poisoning is to immediately transfer the seahorses into clean, well-aerated saltwater with zero ammonia and zero nitrite aquarium. (In your case, Chris, if the ammonia levels or nitrite levels in the aquarium are elevated, perform a major water change using freshly mixed saltwater that has been detoxified and preadjusted to the same specific gravity and water temperature as your seahorse tank, and then dose the aquarium with SeaChem Stability to boost the biological filtration.)

Exposure to moderate levels of ammonia and nitrite (or excessively high levels of nitrates) can change the normal hemoglobin in the seahorse’s blood stream to a form (i.e., methhemoglobin) that is no longer able to transport oxygen. If this becomes severe enough, it will leave the affected seahorse starved for oxygen, which makes it very weak and fatigued. As a result, the affected seahorses may detach themselves from their hitching posts periodically and rest on the bottom, unable to exert themselves in their weakened condition. As you can imagine, being deprived of oxygen really wipes them out in terms of loss of energy and stamina. And it also results in respiratory distress, and rapid, labored breathing as they try to oxygenate themselves and compensate for the lack of normal hemoglobin.

One of the properties of methylene blue is that it can reverse this process and convert the methhemoglobin in the red blood cells back into normal hemoglobin, which can then pick up and transport oxygen again as usual. That’s why it is so helpful in relieving shipping stress and treating ammonia exposure and nitrite poisoning. For this reason, you may want to pick up some methylene blue at your local fish store and keep it on hand in case it is ever needed (the Kordon brand of methylene blue is best, in my opinion).

The usual criteria for determining whether or not methylene blue is needed to help seahorses recover from exposure to high levels of ammonia is their respiration. If the seahorse has labored breathing — huffing or rapid respiration — then methylene blue is called for. Likewise, if the seahorse is experiencing convulsions or its behavior otherwise indicates it is suffering from more than temporary disorientation and loss of equilibrium, such as lying prostrate on the bottom, unable to right itself again at all after two or three hours have passed, it may benefit from methylene blue to assist its recovery.

When that’s the case, hobbyists may want to consider a quick dip in methylene blue. Commonly known as “meth blue” or simply “blue,” this is a wonderful medication for reversing the toxic effects of ammonia and nitrite poisoning. Methylene blue transports oxygen and aids breathing. It facilitates oxygen transport, helping fish breathe more easily by converting methemoglobin to hemoglobin — the normal oxygen carrying component of fish blood, thus allowing more oxygen to be carried through the bloodstream. This makes it very useful for treating gill infections, low oxygen levels, or anytime your seahorses are breathing rapidly and experiencing respiratory distress. It is the drug of choice for treating hypoxic emergencies of any kind with your fish. However, methylene blue will destroy nitrifying bacteria so it should be used in a hospital tank or as a brief bath or dip only (if used in an established aquarium, it will impair the biological filtration and the tank may need to be cycled all over again).

Here is some more information that may be helpful if you ever need to treat with methylene blue, for any reason:

If you can obtain the Kordon brand of Methylene Blue (available at most well-stocked local fish stores), there are instructions for administering it as a very brief, concentrated dip are as follows:

For use as a dip for treatment of fungus or external parasitic protozoans and cyanide poisoning:
(a) Prepare a nonmetallic container of sufficient size to contain the fish to be treated by adding water similar to the original aquarium.
(b) Add 5 teaspoons (24.65 ml) per 3 gallons of water. This produces a concentration of 50 ppm. It is not recommended that the concentration be increased beyond 50 ppm.
(c) Place fishes to be treated in this solution for no longer than 10 seconds.
(d) Return fish to original aquarium.

When you administer such a dip, hold the seahorse in your hand throughout the procedure and time it closely so that the dip does not exceed 10 seconds.

And here are Kordon’s instructions for administering the methylene blue in a hospital tank if longer-term treatment seems appropriate to reverse more severe cases of nitrite poisoning and ammonia toxicity:

As an aid in reversal of nitrite (NO2-) or cyanide (CN-) poisoning of marine and freshwater aquarium fishes:
(a) Remove carbon filter and continue to operate with mechanical filter media throughout the treatment period.
(b) Add 1 teaspoon of 2.303% Methylene Blue per 10 gallons of water. This produces a concentration of 3 ppm. Continue the treatment for 3 to 5 days.
(c) Make a water change as noted and replace the filter carbon at the conclusion of the treatment.

See the following link for more information on treating with Kordon’s Methylene Blue:

Click here: KPD-28 Methylene Blue
http://www.novalek.com/archive/kpd28.htm

If you obtained a brand of methylene blue other than Kordon, just follow the instructions the medication comes with.

Just be sure that you don’t have the methylene blue to your main tank, since that can have a negative impact on the biological filtration.

If you can provide me with photographs, that could also help be in diagnosing this problem, Chris. You can contact me off list at the following e-mail address and attach any photos that might be helpful to your e-mail:

[email protected]

Good luck in the meantime.

Respectfully,
Pete Giwojna, Ocean Rider Tech Support