Mycobacterium marinum

Good day, gentle reader. In this short post, I will recap a simple medical procedure that I assisted with last week. I was not able to photograph the animal or tools so words will have to suffice.

We have a snow-flake moray eel (Echidna nebulosa) that has been in pretty bad shape for some time. It has been residing in a very large display of many thousands of gallons along with myriad other reef fishes. The animal has lumps and lesions along its dorsal surface, especially toward the head. The animal has been treated with antibiotics on several occasions to no avail. It has also had to be force fed with a tube on and off throughout its nearly year-long illness. The exact pathogen is not know though we suspect "fish tuberculosis" caused by Mycobacterium marinum, symptoms of which include raised bumps and lesions. This bacteria can infect fish but it can also infect aquarists. For this reason, it was very important to glove-up for the procedure.

The animal is a mature individual of nearly 3 ft in length with a body depth of about 4 in. It had been caught out of the display by divers and had been residing in a large holding tank for about 5 weeks during which time it had not eaten. The goal of the procedure was to obtain a sample from inside one of the large lumps and send it to the lab for positive ID. If in fact it turned out to be Mycobacterium marinum, the eel would have to be euthanized as there is no treatment.

Even though the eel's health was severely compromised, it was still a large and powerful animal capable of inflicting a painful bite. To get the sample, we had to anesthetize the animal with MS 222 (Tricaine Methanesulfonate) which is commonly used for this purpose. Too much MS 222 would mean death for the eel. Too little would mean we were in danger of being bitten. Catching the animal, even in a holding tank with no decor, was a challenge but we finally prevailed. We then introduced the eel into the tub of anesthetic and waited.

After about 5 minutes, the eel was docile enough to be handled. I was in charge of holding the animal while my partner got the sample. Getting a grip on a slippery eel isn't easy. We used paper towels in our gloved hands to cradle the animal. Procuring said sample involved sterilizing the area with an alcohol wipe and then making a small incision in one of the lumps with a scalpel. Then a sterile swab would be inserted into the incision to collect a sample and then placed in a sterile tube to send to the lab. When my partner applied the alcohol, it definitely got the eel's attention and the animal quickly slithered out of my hands. Luckily it didn't turn around and bite me. We realized it needed a bit more time in the MS 222 bath before we could do what we needed to do.

Another 5 minutes did the trick and we were off and running. Again, I held the animal while the site was cleaned, incision made and sample taken. It all came off without a hitch. We're now waiting to hear from the lab. As mentioned, if it is M. marinum, the animal will be euthanized. If it's something else, we will treat accordingly.

It is sad to see such a glorious animal in this condition but I was surprised at how matter-of-factly I handled the situation. I guess having worked with fish for a while now, I'm a bit hardened to the ups and downs of life in salt water. I was also surprised at the power of this animal having never handled a fish of this size. It was like one long muscle. Finally, I was struck by the beauty of the eel's markings. Held partly out of the water, the patterns were extremely clear and vibrant. Even in its severely compromised state, this animal was absolutely gorgeous.

Hopefully, we'll get some good news, but we pretty much expect the worst.

Thanks for reading and may you and your fish be ever free of Mycobacterium marinum.

Best, Paul

Update: The lab results came back positive for "Myco." Sadly, we had to euthanize the animal using the same MS 222 that we used as an anesthetic only at a higher concentration.