page_title: Fish disease and parasites
section_title: Disease
hierarchical_section_title: Fish disease and parasites / Disease
caption_attribution_description: English: A vet, giving a goldfish an injection because of an eye infection. The name of the goldfish is Hannes. GNU-FDL. Picture can be published with permission of the vet.
context_page_description: Like humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and non-specific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. If pathogens breach these defences, fish can develop inflammatory responses that increase the flow of blood to infected areas and deliver white blood cells that attempt to destroy the pathogens.
  Specific defences are specialised responses to particular pathogens recognised by the fish's body, that is adaptative immune responses. In recent years, vaccines have become widely used in aquaculture and ornamental fish, for example vaccines for furunculosis in farmed salmon and koi herpes virus in koi.
  Some commercially important fish diseases are VHS, ich and whirling disease.
context_section_description: All fish carry pathogens and parasites. Usually this is at some cost to the fish. If the cost is sufficiently high, then the impacts can be characterised as a disease. However disease in fish is not understood well. What is known about fish disease often relates to aquaria fish, and more recently, to farmed fish.
  Disease is a prime agent affecting fish mortality, especially when fish are young. Fish can limit the impacts of pathogens and parasites with behavioural or biochemical means, and such fish have reproductive advantages. Interacting factors result in low grade infection becoming fatal diseases. In particular, things that causes stress, such as natural droughts or pollution or predators, can precipitate outbreak of disease.
  Disease can also be particularly problematic when pathogens and parasites carried by introduced species affect native species. An introduced species may find invading easier if potential predators and competitors have been decimated by disease.
  Pathogens which can cause fish diseases comprise: 
  viral infections, such as esocid lymphosarcoma found in Esox species.
  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
caption: A veterinarian gives an injection to a goldfish
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