Here's a breakdown:
* Pfiesteria:
* "Pf" is pronounced like "F"
* "ie" is pronounced like "ee" in "see"
* "ste" is pronounced like "ste" in "step"
* "ria" is pronounced like "ree" in "tree"
* piscicida:
* "pis" is pronounced like "piss"
* "ci" is pronounced like "si" in "sigh"
* "cida" is pronounced like "si-duh"
Let me know if you'd like to hear an audio pronunciation!