64
CARL J. SINDERMANN
( c ) The marine environment is less amenable to manipulation than
is the fresh-water environment, and problems of disease control in the
sea have seemed insurmountable to some people.
The widely-scattered world literature on marine fish diseases
encompasses a body of knowledge that is growing rapidly with increasing
scrutiny of the oceans and their inhabitants as actual and potential
food sources for an expanding human population. The species of
fishes studied are primarily members of commercially important
groups such as gadoids and clupeoids, and attention has been paid t o
those conditions which affect survival or marketability. Diseases of
marine fishes are important economically because they : ( 1 ) reduce the
number of fish available to man; or (2) reduce the quality of fish as
food. Important to (1) are epizootics and resultant mass mortalities
caused by infectious agents. Less conspicuous but also important are
" background " effects of disease that result in continuous direct or
indirect subtraction of individuals from a population. Important t o
(2) are parasites that inhabit and sometimes degrade the muscles of
marine fishes. Conspicuous in this group are the Microsporidea,
Myxosporidea, larval worms and tissue-invading copepods.
Infectious diseases produce dramatic effects, such as epizootica
and mass mortalities. Bacteria, fungi and protozoans have all been
implicated in marine diseases of serious consequence. Severe shortterm effects of outbreaks on population size and on commercial landings
have been observed in Atlantic herring, white perch and other species.
Repeated outbreaks of certain infectious diseases, such as red disease
of eels and Ichthyophonus disease of herring, have been recorded.
Among the invasive diseases, larval cestodes, trematodes and
nematodes can be found, often in large numbers, in the flesh and
viscera of marine fishes, where they may interfere with metabolic
activities and with growth, or they may otherwise reduce the value of
the parasitized fish to man. Tissue-invading copepods may act in
similar ways. Enzootic centers exist for certain parasites, for example
larval nematodes and some copepods ; occasionally parasites such as
monogenetic trematodes increase in abundance locally to produce
epizootics.
Abnormalities, including tumors and skeletal deformities, are
known for many marine species. Most of the morphological variations,
other than tumors, can probably be attributed to defects in embryonic
development-in fact a wide range of abnormalities has been seen in
larval fishes, especially those reared in environments in which oxygen,
salinity, light or other factors deviated from normal.
Studies of captive marine fishes have provided much information
CARL J. SINDERMANN
( c ) The marine environment is less amenable to manipulation than
is the fresh-water environment, and problems of disease control in the
sea have seemed insurmountable to some people.
The widely-scattered world literature on marine fish diseases
encompasses a body of knowledge that is growing rapidly with increasing
scrutiny of the oceans and their inhabitants as actual and potential
food sources for an expanding human population. The species of
fishes studied are primarily members of commercially important
groups such as gadoids and clupeoids, and attention has been paid t o
those conditions which affect survival or marketability. Diseases of
marine fishes are important economically because they : ( 1 ) reduce the
number of fish available to man; or (2) reduce the quality of fish as
food. Important to (1) are epizootics and resultant mass mortalities
caused by infectious agents. Less conspicuous but also important are
" background " effects of disease that result in continuous direct or
indirect subtraction of individuals from a population. Important t o
(2) are parasites that inhabit and sometimes degrade the muscles of
marine fishes. Conspicuous in this group are the Microsporidea,
Myxosporidea, larval worms and tissue-invading copepods.
Infectious diseases produce dramatic effects, such as epizootica
and mass mortalities. Bacteria, fungi and protozoans have all been
implicated in marine diseases of serious consequence. Severe shortterm effects of outbreaks on population size and on commercial landings
have been observed in Atlantic herring, white perch and other species.
Repeated outbreaks of certain infectious diseases, such as red disease
of eels and Ichthyophonus disease of herring, have been recorded.
Among the invasive diseases, larval cestodes, trematodes and
nematodes can be found, often in large numbers, in the flesh and
viscera of marine fishes, where they may interfere with metabolic
activities and with growth, or they may otherwise reduce the value of
the parasitized fish to man. Tissue-invading copepods may act in
similar ways. Enzootic centers exist for certain parasites, for example
larval nematodes and some copepods ; occasionally parasites such as
monogenetic trematodes increase in abundance locally to produce
epizootics.
Abnormalities, including tumors and skeletal deformities, are
known for many marine species. Most of the morphological variations,
other than tumors, can probably be attributed to defects in embryonic
development-in fact a wide range of abnormalities has been seen in
larval fishes, especially those reared in environments in which oxygen,
salinity, light or other factors deviated from normal.
Studies of captive marine fishes have provided much information