9.6.1 Acanthocephalus spp.
Several species of Acanthocephalus have been described
from salmonids from Japan, North and South America.
Fish may tolerate heavy infections in the intestine, but this
results in chronic catarrhal inflammation, haemorrhage,
compression of intestinal folds and loss of columnar appearance of epithelial cells, and consequently poor growth. The
host’s epithelial lining is eroded through the action of the
armed retractable proboscis. Spindle-shaped eggs are produced in the intestinal tract and pass into the water where
they are ingested by various isopods and amphipods. The
representatives of the genus Acanthocephalus are primarily
recognised by their morphology and the number of hooks on
the proboscis. In stained histological sections the
distinguishing features include a thin, non-rigid acellular
cuticle and thick hypodermis consisting of layers of fibres
overlying thin bands of circular and longitudinal smooth
muscle. In cross section, distinctive lacunar channels are
seen as clear oval or circles in the hypodermis. Consequently
raised subserosal nodules occur in the gut mucosa with a
severe granulomatous reaction (Fig. 9.46).
9.6.2 Pomphorhynchus spp.
Pomphorhynchus laevis is a frequent parasite of European
and North American fresh water fish. Grayling, Atlantic
salmon, brown and rainbow trout are reported susceptible
hosts. P. patagonicus is reported affecting several fresh
water species including rainbow trout in fresh water lakes
in the Patagonia region of South America (Fig. 9.47).
A hooked proboscis penetrating the intestine wall results in
a chronic proliferative host response with the formation of
whitish, fibrous capsule of inflammatory cells including
EGCs and fibroblasts. Mechanical damage to the intestinal
epithelium is the principal lesion with severe infections
blocking the lumen and depriving the host of nourishment.
In some cases the parasite may penetrate through the intestine and cause a proliferative reaction in other organs such as
the liver and pancreas.
Diagnosis is based upon the finding of adult worms in
the intestine or invasive larvae within the body cavity. The
shape of the proboscis, the number and arrangement of the
hooks are also diagnostic features.
9.7
Maxillopoda
Sea lice are the most economical important parasitic copepod affecting salmon culture worldwide, and typically infest
the external surface of marine and brackish-water fish.
Infestation can result in significant morbidity and mortality
of hosts in addition to being expensive to control (Table 9.2).
9.7.1 Lepeophtheirus salmonis
Lepeophtheirus salmonis is a parasitic marine copepod
belonging to the family Caligidae referred to as sea lice.
These occur on wild and farmed salmonids in both the North
Atlantic and North Pacific oceans and is considered the most
important ectoparasite in salmon farming. Affected species
include Atlantic and Pacific salmon, sea-run strains of rainbow trout, brown trout and Arctic char. Recently L. salmonis
have been shown to develop, although not to complete a full
life-cycle, on the three-spined stickleback in coastal areas of
British Columbia.
Sea lice are seldom reported in large numbers from wild
fish. However, farmed salmon may become heavily infested
Fig. 9.46 Acanthocephalus sp. in the intestine of grayling. Low power Fig. 9.47 Whole mount of Pomphorhynchus patagonicus from rainbow trout
9.7 Maxillopoda
143
Several species of Acanthocephalus have been described
from salmonids from Japan, North and South America.
Fish may tolerate heavy infections in the intestine, but this
results in chronic catarrhal inflammation, haemorrhage,
compression of intestinal folds and loss of columnar appearance of epithelial cells, and consequently poor growth. The
host’s epithelial lining is eroded through the action of the
armed retractable proboscis. Spindle-shaped eggs are produced in the intestinal tract and pass into the water where
they are ingested by various isopods and amphipods. The
representatives of the genus Acanthocephalus are primarily
recognised by their morphology and the number of hooks on
the proboscis. In stained histological sections the
distinguishing features include a thin, non-rigid acellular
cuticle and thick hypodermis consisting of layers of fibres
overlying thin bands of circular and longitudinal smooth
muscle. In cross section, distinctive lacunar channels are
seen as clear oval or circles in the hypodermis. Consequently
raised subserosal nodules occur in the gut mucosa with a
severe granulomatous reaction (Fig. 9.46).
9.6.2 Pomphorhynchus spp.
Pomphorhynchus laevis is a frequent parasite of European
and North American fresh water fish. Grayling, Atlantic
salmon, brown and rainbow trout are reported susceptible
hosts. P. patagonicus is reported affecting several fresh
water species including rainbow trout in fresh water lakes
in the Patagonia region of South America (Fig. 9.47).
A hooked proboscis penetrating the intestine wall results in
a chronic proliferative host response with the formation of
whitish, fibrous capsule of inflammatory cells including
EGCs and fibroblasts. Mechanical damage to the intestinal
epithelium is the principal lesion with severe infections
blocking the lumen and depriving the host of nourishment.
In some cases the parasite may penetrate through the intestine and cause a proliferative reaction in other organs such as
the liver and pancreas.
Diagnosis is based upon the finding of adult worms in
the intestine or invasive larvae within the body cavity. The
shape of the proboscis, the number and arrangement of the
hooks are also diagnostic features.
9.7
Maxillopoda
Sea lice are the most economical important parasitic copepod affecting salmon culture worldwide, and typically infest
the external surface of marine and brackish-water fish.
Infestation can result in significant morbidity and mortality
of hosts in addition to being expensive to control (Table 9.2).
9.7.1 Lepeophtheirus salmonis
Lepeophtheirus salmonis is a parasitic marine copepod
belonging to the family Caligidae referred to as sea lice.
These occur on wild and farmed salmonids in both the North
Atlantic and North Pacific oceans and is considered the most
important ectoparasite in salmon farming. Affected species
include Atlantic and Pacific salmon, sea-run strains of rainbow trout, brown trout and Arctic char. Recently L. salmonis
have been shown to develop, although not to complete a full
life-cycle, on the three-spined stickleback in coastal areas of
British Columbia.
Sea lice are seldom reported in large numbers from wild
fish. However, farmed salmon may become heavily infested
Fig. 9.46 Acanthocephalus sp. in the intestine of grayling. Low power Fig. 9.47 Whole mount of Pomphorhynchus patagonicus from rainbow trout
9.7 Maxillopoda
143