Your seahorse is suffering from a condition known as Gas Bubble Disease (GBD), but judging from your description I cannot tell which type of GBD he has at this time, and I will need a little more information from you in order to determine the best treatment. GBD is a serious affliction, which will eventually be fatal if you don’t intervene, but it is treatable with a good rate of cure.
Right now I am not certain if your seahorse is suffering from pouch emphysema or subcutaneous emphysema. Pouch emphysema is a form of GBD in which gas builds up within the brood pouch of male seahorses until they eventually become positively buoyant and float at the surface like a cork. As the gas accumulates, the pouch becomes swollen and bloated. This is the most common form of GBD and is fairly easy to treat.
The other form of GBD your seahorse may have is known as subcutaneous emphysema or simply tail bubbles. In this form of the affliction, blisterlike bubbles form just beneath the skin and gradually grow from day to day has gas builds up within them. These external bubbles appear most often on the tail, but may also appear in other parts of the body. In severe cases, the tail bubbles may become so large and extensive that the the tail becomes buoyant and the seahorse ends up floating. This form of GBD responds well to treatment with the right medication.
If you can let me know which form of GBD you believe your male has, Sandra, pouch emphysema or tail bubbles (or possibly both), I can provide you with detailed instructions on how to treat him. Would you say that your male has a bloated pouch or blisterlike bubbles on his tail? When treatment is begun while the seahorses still eating, the chances for a complete recovery are very good.
Best of luck resolving this problem, Sandra. If you can give me a few more details and help me determine which type of GBD your male has, we can begin treatment immediately. I hope to hear back from you very soon.