Disease
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
- 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
Read more about this topic: Fish Diseases
Famous quotes containing the word disease:
“In a country where misery and want were the foundation of the social structure, famine was periodic, death from starvation common, disease pervasive, thievery normal, and graft and corruption taken for granted, the elimination of these conditions in Communist China is so striking that negative aspects of the new rule fade in relative importance.”
—Barbara Tuchman (1912–1989)
“The fantasies inspired by TB in the last century, by cancer now, are responses to a disease thought to be intractable and capricious—that is, a disease not understood—in an era in which medicine’s central premise is that all diseases can be cured.”
—Susan Sontag (b. 1933)
“Hastiness and superficiality are the psychic diseases of the twentieth century, and more than anywhere else this disease is reflected in the press.”
—Alexander Solzhenitsyn (b. 1918)