Yes, from the swimming behavior you describe it certainly does sound as though Sydney is having a problem with negative buoyancy. This can be either due to an underinflated swimbladder or to ascites, a buildup of fluid within the coelom or abdominal cavity (often associated with kidney problems). If your female, Sydney, is not bloated then I suspect that the negative buoyancy is the result of an underinflated swimbladder.
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. 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).
When the swim bladder is inflated with just the right amount of gas, the seahorse achieves neutral buoyancy, which just means that if neither tends to rise or sink. It is thus weightless in the water, with the buoyancy from its gas bladder exactly canceling out the pull of gravity. This facilitates swimming and makes holding its body upright effortless.
But a number of things can disrupt the normal functioning of the gas bladder and the gas gland that inflates it, resulting in either too little or too much gas being secreted into the swimbladder. When too much gas is secreted into the swimbladder the seahorse becomes too buoyant. Hyperinflation of the swimbladder thus results in positive buoyancy and the tendency to float. Likewise, if too little gas is secreted into the swimbladder, exactly the opposite occurs in the seahorse becomes too heavy. Under inflating the gas bladder therefore results in negative buoyancy and the tendency to sink.
So I think you are correct, Claire, and that your female is struggling with an underinflated swim bladder or gas bladder. The resulting negative buoyancy makes it difficult for the armor-plated seahorse to swim normally, rise from the bottom, or even hold itself erect. An underinflated swim bladder is sometimes a problem a seahorse can correct on its own, as more gas is gradually secreted into the swim bladder from the gas gland. However, this is a gradual process and may take days to accomplish. But if Sydney has been this way for an extended period, lurching from hitching post to hitching post and making crash landings frequently, then I suspect some sort of the swim bladder disorder.
For example, an underinflated gas bladder can also result from infection, and I have seen several cases of swim bladder disease that were associated with internal parasites (digenes), which sometimes also contribute to generalized weakness, and I would ordinarily recommend treating your seahorses with a good antiparasitic that is effective against internal parasites, such as metronidazole or praziquantel as a precaution.
But I know you have recently completed treating your main tank with metronidazole/praziquantel, Claire, so you have already covered that possibility. Hopefully, Sydney will be able to correct the situation herself in time, I gradually releasing more gases into her swimbladder via the gas gland. If not, you can always consider administering an antibiotic orally via gutloaded shrimp, but I am not entirely certain if that would be appropriate or helpful in a case like this.
In the meantime, just make sure your pH and dissolved oxygen levels are on the mark, keep your temperature in the comfort zone for H. angustus, and maintain optimum water quality.
Best wishes with all your fishes, Claire!
Post edited by: Pete Giwojna, at: 2009/07/08 21:34