Zoanthids - How Your Saltwater Aquarium Could be Your Silent Killer

Posted by sharon seals on

We regularly talk about things like how to keep our tank parameters in check, what a shame it is that uneducated hobbyists are sold fish in tiny tanks, and what type of LED lights to buy, but we rarely hear about the dangers of the aquarium hobby. It may be a bit of an exaggeration to say how dangerous it is, but the fact that there are fish and living organisms sold in stores on a regular basis that could actually kill you, and it is never mentioned, is a little ridiculous.

The living organism we are referring to are the popular beginner soft corals, the zoanthids. These soft corals are known for their range of amazing color combos and the fact that, in terms of corals, they are relatively hardy. They prefer less direct lighting, flow and are often found in the murkier bottom areas of a reef in the wild. As long as they feel comfortable, these beauties will multiply like crazy. Because of this, they are easy to frag, which also brings down the price. So far, they are the best choice for beginners in our opinion! The problem is that these corals, not all but a good majority, harbor a powerful defense mechanism called Palytoxin.

The Discovery of Palytoxin

Only recently, in 1971, was Palytoxin actually collected and named. Though the deadly poison has been a well-known thing for quite some time, its most well-known appearance is in the Pacific through the Hawaiian culture. While it has since been discovered in multiple organisms throughout the world, the natives spoke of a specific silent killer and had myths surrounding the random disappearance of the average fisherman. They knew not to disturb certain tide pools and even were said to use an unknown poison on arrows and spears, just as the Amazonians did with Poison Dart Frogs.

At its discovery, studies were conducted on mice to see just how deadly the toxin really was. Interestingly enough, this little heard of poison is apparently one of the most deadly known to man. In fact, just having your hand in the water of a tank with a poisonous zoanthid could infect you with enough to kill you within hours.

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Which Ones are the Deadly Zoanthids?


Unfortunately, scientists have very little information about where the Palytoxin comes from or which zoanthids carry it. There is documentation from when it was first discovered that a certain Zoa strain may be the culprit, but any aquarist knows that the number of available frags out there multiplies daily, and a lot of them look a lot alike.


The fact that most frags are sold by hobbyists to anyone on the market also leads to less documentation than you would think. Not all Zoas can kill you, but be wary about just grabbing any old coral from a random stranger who picked it up from the unknown.


Probably no Need to Worry

The thought of growing the most deadly substance known to man right in your home may be slightly alarming, however, it is unlikely this is the case. If you do have Zoas in your aquarium and you've bought them from an actual supplier, you are most likely fine. Caution can always be exercised though.

Taking Precautions

It is usually recommended to wear gloves when playing around with your tanks for just these types of circumstances, though few of us do. The main reason for the glove recommendation is so that we aren't transferring any unhealthy substances into our well-cared-for tank water, but keeping the growing bacteria inside a tank off of your hands probably wouldn't hurt either. Also, if you have any scratches or cuts, aquarium bacteria can cause a mean infection! An educated aquarist would most likely tell you to wear them too when handling your more sensitive corals, both for their protection and your own.

As far as is known, the Zoas that are deadly only release this toxin at certain times as a defense mechanism when they feel threatened or stressed. If you are worried that you may have a toxic beauty in your reef, at least wear gloves when rearranging. If you are planning on fragging or cutting into the corals, make sure beforehand that you don't have any tiny breaks in the skin and wash well afterward before eating.

The cases are far and few between, and there is a possible fix. The catch to treatment is that you have to know immediately once you have been infected. While we sound like we are discouraging you from adding a beautiful Zoanthid to your fish tank, this is far from the case! We love these beauties, and we hope you do too. We are here to focus on learning about the aquarium hobby and to help educate others about the good, the bad, and the deadly! 


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