DISEASES OF MARINE FISHES
47
parasites can increase costs of packaging up to 80%. Of particular
significance were Sphyrion “ buttons ” in redfish, Porrocaecum larvae
in cod, and Stephanostomurn metacercariae in flounders.
Larval nematodes are most likely to produce consumer complaints
if found in marketed fish. Eustoma (Anacanthocheilus) larvae occur in
mesenteries and gonads of European herring. Mann (1964) reported
them as infrequent in small herring but common in adult herring of
the Norwegian coast. Larval Anisakinae are also common in herring
of the North American east and west coasts. Larval nematodes invade
the liver of gadoids, disrupt normal function and often cause extensive
atrophy. This condition is prevalent in haddock, where larval worms
may occur in the flesh as well. Presence of conspicuous larval cod
worms (Porrocaecurn) in the flesh can lead to rejection of infested fish.
Certain inshore grounds off Canada have not been fished for cod
because of a history of consistently high nematode parasitization.
VI. VARIATIONS IN DISEASE PREVALENCE
Description of the role of disease in marine fish populations must
include consideration of the dynamic relationships of host, parasite
and environment. Some of the consequences of these interactions are
reflected in variations in the occurrence or prevalence of particular
diseases with age of the host, with geographic location within the
host’s range, and with time. Thus, a disease may be characteristic
only of juveniles or only of adults; it may occur in one gulf and be
absent in another ; or it may be abundant today and very rare ten years
from now. Examples of such variability are available, although the
underlying causes are sometimes obscure.
A. Geographic variations
Evidence has accumulated to provide a reasonable picture of
geographic variations in the occurrence and abundance of the parasitic
copepod Sphyrion in redfish of the western North Atlantic. Major
centers of abundance exist in the Gulf of Maine and off the coast of
Labrador; minor centers occur on the south-east slope of the Grand
Bank and in the south-eastern Gulf of Saint Lawrence. The parasite
is absent from other major fishing banks of the western North Atlantic.
Templeman and Squires (1960) have reviewed possible reasons for such
marked variations, which apparently persist from year to year. Redfish
do not undertake extensive migrations and are closely associated with
the bottom; both factors may be important in maintaining enzootic
centers of infestation.
Studies have been made during the past decade of parasitic diseases
47
parasites can increase costs of packaging up to 80%. Of particular
significance were Sphyrion “ buttons ” in redfish, Porrocaecum larvae
in cod, and Stephanostomurn metacercariae in flounders.
Larval nematodes are most likely to produce consumer complaints
if found in marketed fish. Eustoma (Anacanthocheilus) larvae occur in
mesenteries and gonads of European herring. Mann (1964) reported
them as infrequent in small herring but common in adult herring of
the Norwegian coast. Larval Anisakinae are also common in herring
of the North American east and west coasts. Larval nematodes invade
the liver of gadoids, disrupt normal function and often cause extensive
atrophy. This condition is prevalent in haddock, where larval worms
may occur in the flesh as well. Presence of conspicuous larval cod
worms (Porrocaecurn) in the flesh can lead to rejection of infested fish.
Certain inshore grounds off Canada have not been fished for cod
because of a history of consistently high nematode parasitization.
VI. VARIATIONS IN DISEASE PREVALENCE
Description of the role of disease in marine fish populations must
include consideration of the dynamic relationships of host, parasite
and environment. Some of the consequences of these interactions are
reflected in variations in the occurrence or prevalence of particular
diseases with age of the host, with geographic location within the
host’s range, and with time. Thus, a disease may be characteristic
only of juveniles or only of adults; it may occur in one gulf and be
absent in another ; or it may be abundant today and very rare ten years
from now. Examples of such variability are available, although the
underlying causes are sometimes obscure.
A. Geographic variations
Evidence has accumulated to provide a reasonable picture of
geographic variations in the occurrence and abundance of the parasitic
copepod Sphyrion in redfish of the western North Atlantic. Major
centers of abundance exist in the Gulf of Maine and off the coast of
Labrador; minor centers occur on the south-east slope of the Grand
Bank and in the south-eastern Gulf of Saint Lawrence. The parasite
is absent from other major fishing banks of the western North Atlantic.
Templeman and Squires (1960) have reviewed possible reasons for such
marked variations, which apparently persist from year to year. Redfish
do not undertake extensive migrations and are closely associated with
the bottom; both factors may be important in maintaining enzootic
centers of infestation.
Studies have been made during the past decade of parasitic diseases