viral infections, such as esocid lymphosarcoma found in Esox species.[8] bacterial infections, such as Pseudomonas fluorescens leading to fin rot and fish dropsy fungal infections water mould infections, such as Saprolegnia sp. metazoan parasites, such as copepods unicellular parasites, such as Ichthyophthirius multifiliis leading to ich Certain parasites like Helminths for example Eustrongylides