Environmental Engineering Reference
In-Depth Information
infection in salmonids reared in SW has been caused by
C. rogercresseyi
. The monitoring
program of Intesal reported an average value of 3.38 adult
Caligus
per fish between 1999 and
2002. However, an increasing load between 2004 and 2007 was observed with an average of
3, 5 and 10
Caligus
per Coho salmon, rainbow trout and Atlantic salmon, respectively.
Moreover, the abundance levels increased up to 29, 20 and 34
Caligus
per fish in the same
mentioned species in 2007 (Rozas & Asencio, 2007). In order to get relevant information and
establish strategic control measures, the national fisheries service -Sernapesca- established
the Official Monitoring Program focused in marine and estuarine areas (Sernapesca, 2009).
After this program was established and executed, the average load has significantly
dropped (Sernapesca, 2010). However, the lower number of fish in sea sites may also explain
this decrease in parasite loads after the infectious salmon anaemia event in 2007.
Between 1993 and 1994, new pathogens were detected, such as the protozoan
Nucleospora
salmonis
(Bravo, 1995), which clinically affected certain strains of Atlantic salmon in SW; the
metazoan
Kudoa
sp. has been sporadically diagnosed in Atlantic salmon, and the protozoan
Hexamita
, has been described in trout and Atlantic salmon fries in FW (Bluth et al., 2003). In
1995, the presence of an atypical form of
Aeromonas salmonicida
causing mortalities in
Atlantic salmon in SW was confirmed, but was restricted to only a few areas in Los Lagos
region (Bravo, 1999, 2000). However, in recent years, this bacterium has been diagnosed in
other locations of the country and spread widely over many host species, and reported from
FW sites (Godoy et al., 2010). The infection is restricted to Atlantic salmon reared in FW. It
has been more frequently registered in lakes, usually after stress events. Infections are
common in broodstock kept in FW from areas where the infection is endemic. There have
been cases in which infection with atypical
A. salmonicida
is considered secondary in relation
to other infections by bacterial agents such as
Flavobacterium sp
. or
Francisella sp.
and viral
such as Infectious Pancreatic Necrosis virus, IPNv (Godoy, 2009b).
Among the emerging diseases of bacterial etiology with economic impacts in salmonid
farming,
Vibrio ordalli
(Colquhoun et al., 2004) and
V. anguillarum
(Avendaño-Herrera et al.,
2007) are the most important. In Chile, vibriosis occurs mainly in estuarine and sea sites,
resulting in cumulative mortality up to 20%. Since 2003, vibriosis outbreaks due to
V. ordalli
have been occurring in Chile affecting initially Atlantic salmon (Colquhoun, 2004) and
subsequently rainbow trout and Coho salmon.
The first cases of Amoebic Gill Disease (AGD) were reported in Atlantic salmon in 2007
(Bustos et al., 2011; Rozas, 2011). The pathogen agent in Chile is
Neoparamoeba
sp
. with
99.61% of relatedness with
N. perurans
(Bustos et al., 2011; Rozas, 2011). Clinically affected
fish show white patches over the gill arches, excess of mucus and bad general condition.
High salinity due to low rainfall is associated to higher prevalence of the disease. Farm sites
reported with AGD infection showed two times higher risk of ISA outbreaks (Rozas, 2011).
Before 1997, Chilean salmon aquaculture was hit primarily by bacterial diseases. However,
by mid-1998 the presence of a new disease in Atlantic salmon stock was confirmed, known
as viral Infectious Pancreatic Necrosis (IPNv). In Chile, IPNv was first isolated from rainbow
trout with no clinical signs (McAllister & Reyes, 1984). This event was the first report in
South America, suggesting that IPNv was introduced through imported eggs from North
America (McAllister & Reyes, 1984). The virus is widely distributed in the different areas
where salmon farming takes place. IPNv affects Atlantic salmon, and cases in Coho salmon
are considered sporadic; however, in recent years the frequency and virulence of the
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