First of all, let me say that this post is not intended to act as medical advice for anyone. If you suspect any disease or ailment, consult your physician. I am in the medical field and many of my friends joke with me about the diseases which must be coursing through my body from drinking siphoned aquarium water. Of course, this is all in good fun and I rarely drink aquarium water...by choice, that is. The fact of the matter is there are indeed diseases which are not unique to the aquarium hobby, but are certainly more prevelant in those of us who have increased exposure to fish tanks. I have included this post as a single piece of information as I am asked quite often by friends if I am worried about getting sick from my tank or if they should be worried about getting sick from theirs. Again, I am not an expert in micriobiology or infectious diseases. The information contained herein is from my own personal research and reading on the topic. Mycobacterium marinarum is a bacteria found in both fresh and salt water. Infection occurs when there is skin trauma (cut, scrape) in the water. This allows the bacterium to grow and cause a nodule in the skin. Because this bacteria grows better in cooler areas of the body, your hands, arms,feet and legs are more likely to be affected than other parts of your body. Cases of this disease are very rare, about 3 people in 1 million will be affected annually. Most of these people are those at high risk of exposure to the bacteria: fisherman, swimmers, aquarium workers. Those exposed to salt water are more likely than those exposed to fresh water. People who swim in pools are highly unlikely to be exposed due to the chlorination of pool water. People who are immunocompromised (HIV/AIDS and people on chemotherapy) are more likely to be affected. Affected people will develop a skin lesion: a bluish nodule that can sometimes ulcerate. There are very rare complications but are generally only seen in patients with a poor immune system. Treatment is with oral antibiotics for a period of 2 to 18 months depending on severity of the infection. There is no permanent damage from the nodules and the antibiotic treatment is very effective. Again, this was just a brief snippet about this disease. Hopefully the reassuring statistic of 3 in 1 million will put some people at ease. If any of you wants further information I suggest you read a medical text which has information on the subject. DO NOT rely on infromation you find on the internet (present post excluded ) as this information is very rarely checked by medical professionals so the authors can write whatever they want.