''Saprolegnia'' is a genus of

water moulds Oomycota forms a distinct phylogeny, phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are mycelia, filamentous and heterotrophic, and can reproduce both Sexual reproduction, sexually and Asexual reproductio ...

often called cotton moulds because of the characteristic white or grey fibrous patches they form. Current taxonomy puts ''Saprolegnia'' as a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of the heterokonts in the order Saprolegniales.

Habits

''Saprolegnia'', like most oomycetes, is both a saprotroph and

necrotroph A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...

. Typically feeding on waste from fish or other dead cells, they will also take advantage of creatures that have been injured. An infection is known as

oomycosis Oomycota forms a distinct phylogeny, phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are mycelia, filamentous and heterotrophic, and can reproduce both Sexual reproduction, sexually and Asexual reproductio ...

. ''Saprolegnia'' is tolerant to a wide range of temperature, , but is more prevalent in lower temperatures. While it is found most frequently in freshwater, it will also tolerate brackish water and even moist soil. ''Saprolegnia'' filaments (

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e) are long with rounded ends, containing the zoospores. Saprolegnia generally travels in

colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...

consisting of one or more species. They first form a mass of individual hyphae. When the mass of hyphae grows large enough in size to be seen without use of a microscope, it can be called a

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...

. Colonies are generally white in color, though they may turn grey under the presence of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

or other debris which has become caught in the

fibrous Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...

mass.

Reproduction

It has a

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

life cycle which includes both

sexual Sex is the biological distinction of an organism between male and female. Sex or SEX may also refer to: Biology and behaviour *Animal sexual behaviour **Copulation (zoology) **Human sexual activity **Non-penetrative sex, or sexual outercourse ** ...

and asexual reproduction. In the asexual phase, a

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

of ''Saprolegnia'' releases

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

s. Within a few minutes, this zoospore will encyst, germinate and release another zoospore. This second zoospore has a longer cycle during which most dispersal happens; it will continue to encyst and release a new spore in a process called polyplanetism until it finds a suitable substrate. When a suitable medium is located, the hairs surrounding the spore will lock onto the substrate so that the sexual reproduction phase can start. It is also during this stage of polyplanetism that the ''Saprolegnia'' are capable of causing infection; the most

pathogenic In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

species have tiny hooks at the end of their hairs to enhance their infectious ability. Once firmly attached, sexual reproduction begins with the production of male and female gametangium, antheridia and

oogonium An oogonium (plural oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in larg ...

respectively. These unite and fuse together via fertilization tubes. The

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

produced is named an oospore.

Characteristics of infection

''Saprolegnia'' is generally a secondary

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

, though in the right circumstances, it can act as primary. It most frequently targets fish, both in the wild and in tank environments. Through

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

of the skin, ''Saprolegnia'' will spread across the surface of its host as a cotton-like film. Though it often stays in the epidermal layers, the mould does not appear to be tissue specific. A ''Saprolegnia'' infection is usually fatal, eventually causing hemodilution, though the time to death varies depending on the initial site of the infection, rate of growth and the ability of the organism to withstand the stress of the infection. The extensive mortalities of

salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...

and migratory

trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salmoni ...

in the rivers of western

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

in the 1970s and 1980s in the UDN outbreak were probably almost all ultimately caused by the secondary ''Saprolegnia'' infections. Historical evidence suggest the ''Saprolegnia'' species affecting Australian freshwater fish may be an introduced strain, imported in the 1800s with exotic salmonid species.

References

*Bruno, D.W., and Wood, B.P. (1994). ''Saprolegnia and other Oomycetes''. CABI Publishing *Meyer, F.P. (1991). ''Aquaculture disease and health management''.

External links

''Saprolegnia mixta'' - videoGenetic breakdown - ''Saprolegnia ferax''
{{Taxonbar, from=Q134922 Water mould genera Saprolegniales Fish diseases