Pete Giwojna

Dear seahorse lover:

Many seahorses will feed upside down under certain circumstances. They will often hang with their head down and their tail anchored to a perch above in order to reach live prey or food that is just out of reach beneath them. But it is not at all normal for a seahorse to swim upside down and the fact that your female Hippocampus erectus is doing so indicates that she has a problem.

When a seahorse swims upside down it is usually because it is struggling against positive buoyancy, and the only way it can stay submerged is to use its dorsal fin to push downwards in order to counteract the tendency to float. Positive buoyancy in a female seahorse is typically the result of an overinflated swim bladder or due to gas building up within the abdominal cavity or coelom, and the concern is that the problem will worsen until the seahorse is floating at the surface of the aquarium unable to swim or feed.

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. 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

When the swimbladder is inflated with just the right amount of gas, the buoyancy provided by this gasbag exactly cancels out the pull of gravity, and the seahorse will neither tend to to float nor tend to sink. This condition is known as neutral buoyancy, and it makes it very easy for the seahorse to swim and maneuver almost effortlessly. But when the swimbladder is over inflated with gas, the seahorse will have positive buoyancy and must exert a lot of energy when swimming in order to counteract the tendency to float. And if the swimbladder is underinflated, the seahorse has negative buoyancy and must swim hard in order to avoid sinking.

The first indication of a problem with positive buoyancy is a loss of equilibrium. The seahorse’s center of gravity shifts as excess gas accumulates in its swim bladder or abdominal cavity, and it will have increasing difficulty swimming and maintaining its normal posture, especially if it encounters any current. It will become apparent that the seahorse has to work hard to stay submerged, as it is forced to abandon its usual upright swimming posture and swim with its body tilted forward or even horizontally in order to use its dorsal fin to counteract the tendency to rise.

Does this sound like the sort of thing you’re topsy-turvy female is doing, seahorse lover? Does her abdomen appeared to be swollen or bloated at all? Does she swim upside down all the time or is she able to swim up right in the normal swimming posture when she wants to?

Many times an overinflated swim bladder will correct itself as excess gas is gradually reabsorbed into the bloodstream through the "oval," an oblong region of the swim bladder that is covered with a meshwork of thin blood vessels designed especially for this purpose. In that case, you will need to do nothing; the problem will probably eventually correct itself without any intervention from the hobbyist. But if your female is indeed having a problem with positive buoyancy and it is due to gas building up within its abdominal cavity (internal gas bubble syndrome), then it will be necessary to treat the female with Diamox (the tablet form of acetazolamide) in order to resolve the problem.

Please monitor your topsy-turvy female carefully and let me know if you feel her unusual behavior is due to positive buoyancy, and if you feel treatment with Diamox is appropriate in your case, and I will provide you with suggestions on how to obtain the medication. (It’s a prescription medication and can be tricky to obtain.)

Best of luck with your female H. erectus, seahorse lover! Here’s hoping that she assumed back to normal again.

Pete Giwojna

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