I’m sorry to hear that your new Hippocampus kelloggi has developed a problem with its tail. Unfortunately, quite a few H. kelloggi owners have been having trouble with this species lately and have been losing their seahorses to various health problems. It just doesn’t appear to be a very hardy strain at this stage in its development.
It’s very difficult to say what the bump on its tail may be without being able to examine it. The bump or lump could be a cyst of some sort. For example, pyogranulatomous cysts are often described as pimplelike bumps or nodules and can be symptoms of serious bacterial infections. If that’s the case, it’s a serious problem and the affected seahorse should be isolated and treated with broad-spectrum antibiotics in a hospital tank ASAP! Or it could be a blisterlike tail bubble developing. The blisterlike subcutaneous emphysema that form under the skin of the tail are the first indications of external gas bubble disease, and generally respond very well to treatment with acetazolamide (Diamox). It’s also possible that the bump could be an embedded parasite, perhaps the sporont stage of a protozoan multiplying within a cyst, or maybe metacercariae from digenetic trematodes, or a lesion from a bacterial or fungal infection, a granuloma, or something as simple as a little viral lymphocystis, the last of which requires no treatment and usually clears up on its own.
Like all fish, seahorses do occasionally develop various granulomas, tumors and fibrosarcomas associated with certain diseases or the aging process. Often these are benign and harmless, but they can also develop malignant neoplasms and cancerous tumors. Many marine animals are contracting papilloma virus infections these days, so it’s possible the bump could be a papilloma. If that’s the case, a wart-like viral infection such as papilloma will not respond to any readily available medications and I can suggest no treatment. Many such growths are harmless, just like the warts we ocasionally develop. If you can give me a better description of the bump, or possibly provide a photograph as discussed earlier, I may be able to give you a better idea of what the problem is and how it should be treated. If you can insert one or more digital photographs of the suspicious bump into an e-mail and send it to me at [email protected], that would be very helpful.
In any case, I can tell you that the fact that the bump is growing is an ominous sign and I would take this problem very seriously. If your new Hippocampus kelloggi has had the bump on its tail ever since it arrived three weeks ago, and the bump is due to a bacterial or fungal infection, then the seahorse was ailing when you received it and you should inform the dealer or breeder from which you obtained the seahorse about the problem immediately. If it turns out to be an infection and the seahorse subsequently expires, you may be entitled to a refund or a replacement from whomever sold you an unhealthy seahorse. Can I ask you where you obtained the H. kelloggi?
Please get back to me as soon as possible with a more detailed description of the bump and hopefully some accompanying photographs, and we’ll take it from there.
In the meantime, best wishes with all your fishes!