Sentence:  <WSD>Ichthyotoxins</WSD> are sufficiently widely present in the reef fish of tropical oceans, and with a sufficiently unpredictable occurrence, as to render the large-scale commercialization of snappers, groupers, jack, and other large, marketable fish a chancy business; in some iland groups, such as (it is claimed) Johnston and Phenix, very high percentages of species are toxic. 
Meaning of the word marked with <WSD> tags:  Any toxin produced by fish.