Beware of Poisonous Fish in Saltwater Aquariums

Red Lionfish (Pterois Volitans)
Red Lionfish. Yiming Chen / Getty Images

Caution should be used when deciding if you want to keep a poisonous fish. Some species not only have the ability to inflict a venomous sting that kills other animals, but many can cause toxic poisoning in an aquarium which can result in the death of the other tank inhabitants, not to mention themselves. Fish such as these can also introduce a nasty poke or serious sting to humans as well!

A venomous sting that does not result in the release of plenty of toxins into the aquarium will usually only affect the fish that was stung. This is often seen by a sudden and unexplainable loss of a fish when a stinging fish is present. However, toxic fish poisoning of the whole aquarium can be noticed by how all the fish in the tank are acting. They will suddenly begin to swim erratically, having the appearance of losing their sense of direction. Heavy and rapid breathing will result, the eyes may cloud over, the fins become ragged looking, they lay on the bottom, and in the end, they will convulse and die. All of this can happen in a matter of minutes, depending on the toxicity of the poisonous fish or animal in the aquarium, and how large of a system you have. Generally, the smaller the system, the faster the toxins can act.

If quick action is not taken, ALL can be lost. If it's not too late, immediately remove any living fish and animals from the tank. We had heard that adding AmQuel to a contaminated aquarium helps to buffer and remove some of the effects of fish toxins. We tried this and have found good results. However, you still need to remove any remaining living animals from the aquarium until a complete and thorough tank/equipment cleaning and water change can be done. If the toxin from the poisonous fish is strong enough, sometimes it cannot be completely removed from the aquarium. If after having a toxic fish poisoning you have fish or other marine animals dying for no reason and everything else seems to check out, suspect residual toxins in the rocks, sand, gravel, carbon (if using for filtration), etc. This may warrant a complete strip down and sterilization of the tank to rid yourself of the problem, but this is usually only in extreme cases.

Let's take a closer look at five common fish families that aquarists need to beware of:

Fish in the Family Scorpaenidae are bottom dwellers and are masters at the art of camouflage. Their dorsal, pelvic and anal spines are able to inject poison from a poison-producing tissue along the spine. The effects of this fish family are two-fold. They can inflict venomous stings AND cause toxic tank poisoning, both of which can kill other tank inhabitants. As far as human interaction, stings are usually not fatal (unless you are allergic to the toxin), but are extremely painful and can sometimes persist months after the event occurs. Immediate steps can be taken to lessen the effects of a Stonefish sting, but time seems to be the key to recovery.

The Volitans Lionfish (Pterois volitans) is probably the most common Scorpionfish species kept by saltwater aquarists. The Hawaiian Turkeyfish (Pterois sphex) and the Hawaiian or Green/Dwarf Lionfish (Dendrochirus barberi) are two of the most common Scorpionfishes found in Hawaiian waters and are kept by aquarists as well. Lionfish stings are not fatal (unless you are allergic to the venom), but can be nasty to deal with. As far as the potency of their poison, no telling what it might to do your other tank inhabitants. I remember when I was working in a doctors office (long before I knew anything about saltwater aquariums) and we had a tank in the waiting room with two beautiful Volitans Lionfish in it, along with some other nice marine critters. One day just before our lunch hour the maintenance guy came to clean the tank and got stung. He immediately took himself to the emergency room, as he was in extreme pain and his hand started to redden and swell up. When we returned from our lunch hour, EVERYTHING in the tank was dead!!

No matter how hard we tried to re-establish the tank with new saltwater animals, everything just kept dying. The doctor finally got fed up, completely stripped the tank and started over with a freshwater tank, with no further problems after doing so. In regards to the maintenance guy, he was fine, but complete recovery from the injury took some time. Make note, it is wise to wear rubber gloves for protection when dealing with any potential stinging marine animal.

The docile looking Leaf fish falls into this family, so caution is advised when dealing with these fish as well.

When startled, frightened or harassed, the fish in this family have the ability to release a fatal toxin from their bodies. That's why we dubbed them with the name Neutron Bomb Boxfish. They can kill every living thing in your aquarium, including the themselves, leaving you with just your decorations, rocks and tank standing. Use extreme caution when mixing these fish in an aquarium, unless you want to take the risk of possibly loosing everything. If you desire to keep them, they are best kept in a non-aggressive species tank. Cowfish are also part of the Ostraciidae family and have this same characteristic trait.

Pufferfishes (Family Tetraodontidae (Chonerhinidae)

Also known as Balloon, Blow, Globe, Toadfishes, and referred to as Fugu, these fish have the ability to store tetrodotoxin, a toxin found in some species of Pufferfishes. Considered to be a delicacy by the Japanese, Fugu can result in severe food poisoning in humans, sometimes resulting in death, if not prepared properly. Two of the most common types of Fugu in Hawaii are the Green Whitepot/Stars & Stripes Puffer (Arothron hispidus) and the Brown Whitespot/Speckled Puffer (Arothron meleagris). Some of these fish have the ability to exude their toxins too, so caution should be used when mixing these fish in your aquarium. We have had the experience of putting a Brown Whitespot Puffer in a catch bucket with a few other fish while collecting, and when we brought the fish up from diving to take them home, everything in the bucket was dead.

Some fish in the Sharp-Nosed Puffer Family (Canthigasteridae) fit into the Tetraodontidae category. We were told, years ago when we started our fish business, that the Spider-Eye Puffer (Canthigaster amboinensis) is one of the most toxic puffers in the Canthigaster Family. Caution should be used, as some of the fish in the Canthigaster Family can exude a toxic poison.

Tobias Heinloth / Getty Images

Squirrelfishes (Family Holocentridae

The dorsal spines of Squirrelfishes have the capability to inflict a nasty poke that can result in something in comparison to a mild bee sting. For some people, this is merely a painful nuisance, but to others, it may cause more serious problems. Nothing to the point of resulting in death, just redness and swelling that may take time to recover from.

In closing, while some of these fish families do not have the capability to exude their toxins, some do have parts of their bodies that can be toxic. If left in a tank after death, other fish may eat the flesh and become sick or possibly die.

We cannot stress enough that being prepared for potential problems that may arise from owning any of these fish and that knowing all you can about them is of the utmost importance. To learn more about poisonous/venomous fish, as well as dangerous Octopuses, Nudibranchs/Sea Slugs and other marine animals, refer to these resources:

  • Poisonous/Venomous Species Resources
  • Human First-Aid Resources for Cuts, Bites & Stings
Humberto Ramirez / Getty Images