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International Journal of Aquaculture, 2014, Vol.4, No.04
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26
and later its causative agent, IHHNV, was first
described as the cause of acute epizootics and mass
mortalities (> 90%) in juvenile and subadult of
L.
stylirostris
farmed in super-intensive raceway systems
in Hawaii (Brock et al., 1983; Lightner et al., 1983,
1983a; Brock and Lightner, 1990). Shortly after its
discovery in
L. stylirostris
, the virus was found in
L.
vannamei
being cultured at the same facility in Hawaii
and these
L. vannamei
were shown to be
asymptomatic carriers of the virus (Lightner et al.,
1983a; Bell and Lightner, 1984). Hence, the economic
and production impacts of IHHNV infection in
L.
vannamei
are due to reduced and irregular growth and
small sized shrimp at harvest and not to elevated
mortality. To mitigate this effect, several strategies
have been used. With one strategy, selected lines of
L.
stylirostris
, which were not only resistant to IHHN
disease, but are also refractory to infection, were
developed (Dhar et al., 2001). IHHNV-free lines of
L.
vannamei
were also developed as SPF (specific
pathogen-free) lines and these stocks were the first
developed in the SPF stock development program
(Pruder et al., 1995).
2.3 White muscle disease
In the present study WMD (White muscle disease)
was observed at shrimp farms in Tamilnadu and
Andrapradesh. The epizootic of WMD was first
recorded in November 2001 in few hatchery reared PL
of
M
.
rosenbergii
in Andrapradesh and Tamilnadu
states. More than 18 cases of WMD in freshwater
prawn hatcheries with PL mortalities ranging from
30% to 100% were recorded from November 2001 to
December 2002. The first sign related to this disease
was the poor feeding (mineral deficiency in water,
poor quality feed) and lethargy of the prawns
especially during the first 5 days of PL settlement
resulting in slow mortality (Figure 4 & 5).
Figure 4 White muscle disease in bigger size
L. vannamei
As the morphological and clinical signs of the disease
reported by Chen et al. (2001) were similar to the
WMD recorded in this study. It is likely that the
involvement of the Gram-positive
cocci
,
Lactococcus
garvieae
in WMD
found by those workers could
possibly have been a secondary infection. The disease
progressively destroyed the abdominal muscular
organization of the prawns especially the striated
muscles finally leading to mortality. Several authors
reported white muscle disease in shrimps and prawns
(Chen et al
.,
1992; Sudhakaran et al, 2006; Ravi et al.,
2009)
.
Besides the above, this white muscle disease
also recorded in
L. vannamei
in the present study.
Figure 5 White muscle disease in small size of
L. vannamei
2.4 White gut disease (WGD)
In the present study white gut disease observed in
L.
vannamei
shrimp farms from Tamilnadu and
Andrapradesh. Vibriosis is one of the major disease
problems in shellfish and finfish aquaculture.
Vibriosis is a bacterial disease responsible for
mortality of cultured shrimp worldwide (Lightner and
Lewis, 1975; Adams, 1991; Lightner et al., 1992;
Lavilla-Pitogo et al., 1996; Lavilla-Pitogo et al., 1998;
Chen et al., 2000).
Vibrio
species are widely
distributed in culture facilities throughout the world.
Vibrio
-related infections frequently occur in hatcheries,
but epizootics also commonly occur in pond reared
shrimp species. Vibriosis is caused by gram-negative
bacteria in the family Vibrionaceae. Outbreaks may
occur when environmental factors trigger the rapid
multiplication of bacteria already tolerated at low
levels within shrimp blood (Sizemore and Davis,
1985), or by bacterial penetration of host barriers. The
exoskeleton provides an effective physical barrier to
pathogens trying to penetrate the external surface of
crustaceans, as well as the foregut and hindgut (Figure
6A & B).