The soapfish

 A type of Grouper, not found, and found on Wikipedia (the astute observer will not that https://en.wikipedia.org/wiki/Grammistin has a link to soapfish, which takes you to the main Grouper article.  Grammistin is the "soap" that the soapfish creates. 

The species in the tribes Grammistini and Diploprionini secrete a mucus-like toxin in their skin called grammistin, and when they are confined in a restricted space and subjected to stress, the mucus produces a foam that is toxic to nearby fish. These fishes are often called soapfishes. They have been classified either as their own families or within subfamilies,^[13] although they are classified by the 5th Edition of the Fishes of the World, classifies these two groups as tribes within the subfamily Epinephelinae