Coloured scanning electron micrograph (SEM) of a Saprolegnia parasitica infected salmon egg. The fungus causes saprolegniosis (water mould disease) which affects wild and cultured freshwater fish and fish eggs worldwide. The disease is characterised by abundant mycelial growth on the egg surface, first established on dead eggs and then extending to neighbouring healthy eggs. In fish, the fungus invades the skin of the head or fins with subsequent spread over the entire body. Saprolegniosis is mostly reported from temperate areas, such as Northwest Europe, Chile, Japan and Canada, where it has a large impact on fish health and the aquaculture industry. Magnification: x10 when printed at 10cm wide.