The there are more than a few

present need to increase the world supply of food for the mounting human
population has resulted in the development of exhaustive production of aquatic
life under controlled conditions. In intensive fish culture the fishes are reserved
at high densities in an inadequate space and provided with supplementary
feeding. Hard work have also been in steps forward to culture the fish in
sewage-fed ponds or other extraordinary conditions such as to bring up them in
warm water used for cooling atomic reactors at optimum temperature all through
the year. Rearing the fish in high compactness in limited water with
supplementary feeding, keeping it at relatively high temperature level and the
risks of pollution are all factors predisposing to the increase of serious
disease problems in fishes. Among the freshwater mycotic fish diseases
saprolegniosis disease is one of the most economical diseases. Saprolegniaceous
fungi are usually known as water molds, are ubiquitous constituent of aquatic environment
and are capable of growth and reproduction throughout the year. Oomycetes are traditional
saprophytic opportunists, multiplying on fish that are physically injured,
stressed or infected (Pickering and Willoughby 1982a). Nevertheless there are more
than a few reports of Oomycetes as primary infection agents of fish (Willoughby
1978, Pickering and Christie 1980). These water molds are the most significant
fungi affecting cultured fish and are measured by some next only to bacterial
disease in terms of economic importance to aquaculture (Meyer 1991). Numerous
species of Saprolegniales infecting fish, fish eggs, amphibians and crustaceans
have a major impact on freshwater ecosystem (Densmore and Green, 2007; Fernandez-Beneitez
et al.,2008; Kiesecker et al.,2001b; McAllister, and Robison 2016).
Saprolegnia parasitica and Saprolegnia diclina are closely related
and are the best studied aquatic oomycetes of the order Saprolegniales
(Dieguez-Uribeondo et al., 2007). The
Salmon fish farming of countries with temperate climate, such as North-west
Euorpe, Chile, Japan and Canada are mostly reported to be infected by S. parasitica and S. diclina. (Hussaein & Hatai 2002, Gordon Ritchie, personal
communication) stated that there are losses estimated at tens of pounds annually
in the salmon aquaculture business in Scotland, Scandinavia, Chile, Japan,
Canada and USA. 50% “winter kill” in catfish was caused by S. parasitica in USA resulted in economic
loss of 25 million (Bruno and Wood 1999). The rapid increase in the aquaculture
production of salmonids has been followed by a rise in several diseases. In
particular, Saprolegniosis can account for at least 10% of the annual economic
loss in salmonids. (Sandoval-Sierra et
al., 2014), also Sandoval-Sierra et
al.,2014; represents the first detailed molecular characterization of  Saprolegnia
species involved in Saprolegniosis in Chile, and the first study showing
specific association of different Saprolegnia
species with different stages in the salmonid life cycle.


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