Aquaria Information from



   The biggest thing a fish has to worry about in the wild is being eaten by a bigger fish. Most successful species have developed a defense to prevent this. Those which most concern the fish handler are the toxic chemicals produced, usually in conjunction with sharp spines, by catfish and scorpion fish. 

   Toxins are generally grouped into two types: hemotoxin, which acts predominantly on blood and soft tissue, and neurotoxin, which interferes with the transmission of nerve impulses. Although both types of toxins cause some type of distress, the neurotoxic substances produced by scorpinidae are by far the most dangerous. 

   Anyone who has handled freshwater catfish will eventually find out what a mild hemotoxin feels like. It stings, producing an ache which can last half an hour. But usually that's the end of it. You should be careful of the spines on the dorsal and pectoral fins of any freshwater catfish. 

   Saltwater catfish are neurotoxic and can give a very serious sting. Other neurotoxic fish are all types of lion fish and stone fish. Care should be taken to avoid stings. 

   Puffer fish, both brackish and salt water, have a substance called tetrodotoxin in their bodies. It is a deadly neurotoxin. Fugu (puffer meat) is prepared in Japan by special chefs who separate the poisonous parts from the non-poisonous parts. Still, people die every year from eating it! All puffers should be considered toxic and not handled with bare hands, especially if open cuts are present. 

   There are a few toxic fresh water fish not in the catfish family. Freshwater groupers and freshwater stonefish should be considered toxic, and all scats have toxic dorsal fins.

   In your collection you may have several species of tarantulas and emperor scorpions. These animals are primarily hemotoxic, and although not considered deadly, should be handled very carefully. There are other types of scorpions but many stores declines to carry them due to their dangerous nature. 

   Some amphibians have toxic substances. California newts have some of the same toxic substances in their bodies as puffers, and firebelly newts are coated with a toxic slime. If you rub your eyes after handling a firebelly toad, you will experience severe burning from a toxic substance in their skin. Poison tree frogs contain a deadly form of nerve toxin. 

   Different fish and amphibians have different levels of toxins; some produce a combination of hemotoxic and neurotoxic venoms. Familiarize yourself with the characteristics of each species by reading any of several excellent books on fish and reptiles available through the pet industry. 

   Anemones have stinging cells at the end of their tentacles which can cause a rash and swelling ranging from mild to severe, depending on species; most other toxic invertebrates are not carried by pet shops.

   In rare instances people may be allergic to what is an innocuous sting to others. Always be alert for a possible severe reaction from these animals (and bees and hornets as well), and get medical help as soon as possible. A good rule of thumb is to remember that saltwater stings are more dangerous than freshwater stings.

Return to Table of Contents