The Toxin Excreting and Venomous Stinging Fish and Invertebrate Species Profiles Index contains information about marine animals which contain toxins which may affect aquarists and other aquarium inhabitants.
This little fish might look harmless, but when frightened it will release a TOXIC POISON to protect itself. When in the wild if this fish does its thing it can easily escape from its own poison, but in a small aquarium, it poisons itself.
The Hawaiian Sphex Lionfish's Dorsal spines contain a powerful toxin.
The Leaf Scorpionfish has venomous stinging spines and therefore should be kept and handled with great caution and care!!
Although related, Porcupine or Burrfishes are not poisonous, but there are many species of Puffers that do excrete tetrodotoxin.
Most of them are ugly (Warty Sea Cucumber), some of them are quite beautiful (Sea Apples), but they all produce toxins. Usually more of a danger to your other tank inhabitants than yourself, these critters should be added to your tank with caution.
The Scrambled Egg Nudibranch or Sea Slug (Phyllidia varicosa) and other Family Phyllidiidae members typically feed on poisonous sponges, of which they store the toxins eaten in their own bodies and then use it as a defense mechanism to prevent predation. This and other related phyllidids are highly toxic animals that should NOT be kept in aquariums.