I am sorry to hear about the problem that your female seahorse has been experiencing for the past week, sir. It does sound like she is having a problem with negative buoyancy (i.e., the tendency to sink), which can result from a number of causes.
For instance, it could be associated with a buildup of fluid within the coelomic cavity, which is a problem that is commonly known as abdominal dropsy or ascites in tropical fish. If the female seahorse’s abdomen appears to be bloated or swollen and she is experiencing problems with negative buoyancy, that would seem to indicate a problem with abdominal dropsy or ascites, which would require treatment with the appropriate medication in order to resolve. (Let me know if that’s the case, Don, and I will provide you with a treatment regimen that should be helpful.)
But laying prone on the bottom of the tank for extended periods could also be an indication of generalized weakness, Don. When that’s the case, the seahorse is too weak to hold itself upright in its normal posture, which can result in the sort of behavior you describe. In seahorses, this sort of generalized weakness is often associated with a lack of oxygen, which can result from insufficient levels of dissolved oxygen in the aquarium water at the bottom of the tank. Low dissolved oxygen levels and high levels of dissolved carbon dioxide can result if there is a lack of surface agitation and/or poor water circulation throughout the aquarium. Many times, this can be corrected simply by increasing the surface agitation and aeration in the aquarium in order to promote better oxygenation and facilitate more efficient gas exchange at the air/water interface.
But oxygen deprivation can also result from spikes in the ammonia or nitrite levels in the aquarium, or even excessively high levels of nitrate. When that happens, the high levels of ammonia/nitrite can convert the hemoglobin in the seahorses red blood cells into a form of the molecule (i.e., methhemoglobin) that is no longer able to transport oxygen. When that’s the case, a seahorse can be starved for oxygen even in an aquarium that has high levels of dissolved oxygen. This is a condition that can correct itself if you can simply eliminate the spike in the ammonia or nitrite levels, or reduce the levels of nitrates to <10 ppm. The best first aid measure for such a problem is to immediately transfer the seahorse into clean saltwater with zero ammonia and zero nitrite. In addition, a quick dip in concentrated methylene blue or a longer bath and less concentrated methylene blue can offer work wonders in such cases because the methylene blue is able to transform methhemoglobin back into the normal hemoglobin molecule, thereby allowing the erythrocytes to transport oxygen normally again. (Note: methylene blue can impair the biological filtration of the aquarium so it should be used as dips or baths, or administered in a hospital tank, rather than being added to the main tank.)
Finally, Don, in seahorses, many times a problem with negative buoyancy is indeed the result of an underinflated gas bladder or swimbladder, as explained in more detail below:
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, Don, 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 a few more days to see if the problem corrects itself.
If it does not, it’s possible that an infection of some sort is interfering with the gas gland, which would then indicate the need for medicating the seahorse in a hospital tank. Medications that combine trimethoprim with sulfa drugs are a good choice for such a problem.
So I would recommend that you check your water chemistry to make sure that the ammonia, nitrite, and nitrate levels are where they should be, sir. If there is any doubt about your water quality, don’t hesitate to perform one or more water changes to make sure that the water quality is optimal. In the meantime, it would also be advisable to increase the surface agitation and aeration in your seahorse setup in order to assure that the dissolved oxygen levels remain nice and high and that the levels of dissolved carbon dioxide remain low.
Let me know if there has been a spike in the ammonia or nitrite levels – or if the seahorse tank is experiencing excessively high levels of nitrate – and I will provide you with directions for performing a dip or bath methylene blue.
If you are going to be waiting to see if the problem resolves itself, it would be a good idea for you to obtain a medication that combines trimethoprim with sulfa drugs in the meantime, so you will have the appropriate medication on hand if the problem with neutral buoyancy does not correct itself. In that event, Don, the medications that I prefer are either Sulfa 4 TMP Powder or TMP Sulfa, both of which can be obtained online without prescription from National Fish Pharmaceuticals.
Sulfa 4 TMP Powder
USE: this is a special blend of four different sulfas that all have different absorption rates and solubility. The sulfas are combined with trimethoprim, which potentiates each other’s ability to kill bacteria. The result is a wide spectrum antibiotic with less chance of resistant strains developing.
DOSAGE: 1/4 teaspoon per 20 gallons of water. (1/2 pound treats 3640 gallons of water.)
25 grams for $15.28
TMP Sulfa (trimethoprim and sulfathiazole sodium)
USE: for treating bacterial infections, both gram-negative and gram-positive. The combination of trimethoprim plus sulfathiazole sodium retards resistant strains from developing. It exerts its antimicrobial effect by blocking 2 consecutive steps in the biosynthesis of the nucleic acids and proteins essential to many bacteria.
DOSAGE: add 1/4 teaspoon per 10 gallons of water every 24 hours, with a 25% water change before each daily treatment. Treat for a minimum of 10 days.
(1/4 pound treats approximately 940 gallons of water.)
*More effective than triple sulfa.
25 grams for $$15.25
You can get both Sulfa 4 TMP Powder and TMP Sulfa from National Fish Pharmaceuticals at the following URL:
Best of luck restoring your female seahorse to normal again, Don.
Pete Giwojna, Ocean Rider Training Tech Support