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mv
AF
N
N
L
L
LP
V
5
μ
m
Fig. 3.1
Transmission electron microscopy of enterocytes in the hindgut of spotted wolffish fry exposed to
V. anguillarum
. Notice the severe necrosis-like damage in lamina propria (LP). Key: mv, microvilli; AF,
apical microvillous brush border fragment; L, lipid droplet; N, nuclei; V, vacuole; arrow, bacteria-like
profile. Scale bar
=
5
μ
m. (Source: Ringø
et al
. 2006. Reproduced with permission of John Wiley & Sons.)
chum salmon
naturally infected
with
V. anguillarum
and
V. ordalii
. The naturally infected
fish showed haemorrhages in muscle, gill and digestive tract. Additionally, necrosis of the
mucosa and muscularis was observed; the posterior region was more severely affected than
the anterior region.
V. ordalii
were commonly revealed in pyloric caeca. Experimentally
V.
ordalii
infected chum salmon showed histopathological changes similar to those observed in
naturally infected fish, and a similar pattern was seen with experimentally infected coho and
Chinook salmon (Ransom
et al.
1984). The authors suggested that the infection began in the
rectum and descending intestine. In another study on ayu, fish were challenged by immersion,
direct contact, cohabitation patch contact (filter paper soaked in bacterial suspension) and intu-
bation (Kanno
et al.
1989). From this study it was concluded that waterborne infection was
the primary mode of transmission of the disease although infection was also established by
oral and anal intubations. Olsson
et al.
(1992) investigated the entry and colonization of
V.
anguillarum
in turbot and a closely related fish species, the dab (
Limanda limanda
L.). All of
the isolates investigated (intestinal isolate 14 from dab, intestinal isolate 4:45 from turbot, skin
mucus isolate 7:12 from turbot and
V. anguillarum
HI 11345) grew in and adhered to turbot
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