Order Saprolegniales is a group of filamentous water molds that are known to cause serious diseases in fish, crustaceans, and other aquatic species. The term Saprolegniales is derived from the Greek words sapros, which means decaying, and legne, which means timber. Saprolegniales are often referred to as water molds or fungus-like organisms because they resemble fungi in both their ecological habits and their morphology. There are various synonyms for Order Saprolegniales, including the following: 1. Saprolegniaceae 2. Oomycetes 3. Peronosporales 4. Pythiales 5. Phycomycetes 6. Water molds 7. Fungus-like organisms Despite having different names, these terms are all used to refer to the same group of organisms that are responsible for some of the most devastating diseases affecting aquatic species.