Wiktionary
ichthyotoxin
n. 1 Any chemical compound that is toxic to fish. 2 Any toxin produced by fish.
Wikipedia
Ichthyotoxin
Ichthyotoxins are compounds which are either toxic to fish or are toxins produced by fish. They include euglenophycin and prymnesins, made by algae and can cause large scale fish deaths, and ostracitoxin made by boxfish.