DISEASES OF MARINE FISHES
61
specific immunological competence in fish further indicates that controlling factors in epizootics are not fundamentally different from
those for other vertebrate groups. Individual variability in susceptibility to pathogens has been demonstrated, and the course of certain
fish diseases shown to be alterable by environmental factors such as
temperature and diet.
Little basis exists for pessimism as to the possibility of disease
control in the sea, despite the seeming immensity of the problem.
True, we now stand in marine disease studies almost where our ancestors
of the Middle Ages did when confronted with the great pestilences of
those days. Yet the advances made since then in understanding and
control of human diseases suggest that technology and techniques
impossible to foresee now can lead to manipulation of the marine
environmeiit and the factors that influence population size of marine
fish. Some approaches have already been suggested. Certain diseases
of inshore species (such as Ichthyophonus disease of herring) might be
artificially supported at a level just high enough to maintain population
resistance at a point where epizootics would not occur. It might be
possible to overfish a population deliberately as soon as evidence of an
incipient epizootic is discovered. These methods are, of course, based
on present knowledge and do not constitute a legitimate portrayal of
future control based on the acquisition of new information.
The severe effects of epizootics on marine fish populations have
been partially documented for Ichthyophonus disease of herring, red
disease of eels and Pasteurella disease of white perch. Significant
reduction in population size was indicated in each outbreak by reduced
catches during the post-epizootic periods. It is tempting to speculate
on the basis of these observations that certain of the unexplained
major past fluctuations in abundance of commercial marine species
may have been caused by disease. As an example, drastic decline in
mackerel abundance on the Atlantic coast of North America in the
late nineteenth century may have been related t o disease. During the
1954-55 fungus-disease epizootic in herring of the Gulf of Saint
Lawrence, mackerel were found to be susceptible and heavily infected.
Mackerel landings in the southern Gulf declined at that time to half
their previous total, and have remained low to the present time.
Available catch records for mackerel of the western North Atlantic,
beginning in 1804, show periodic fluctuations which have been correlated with deviations in air temperatures by Taylor, Bigelow and
Graham (1957), but which may well have had more immediate causes,
such as periodic epizootics. It seems logical that wherever unexplained
catastrophic declines in a fishery have occurred, disease must be
61
specific immunological competence in fish further indicates that controlling factors in epizootics are not fundamentally different from
those for other vertebrate groups. Individual variability in susceptibility to pathogens has been demonstrated, and the course of certain
fish diseases shown to be alterable by environmental factors such as
temperature and diet.
Little basis exists for pessimism as to the possibility of disease
control in the sea, despite the seeming immensity of the problem.
True, we now stand in marine disease studies almost where our ancestors
of the Middle Ages did when confronted with the great pestilences of
those days. Yet the advances made since then in understanding and
control of human diseases suggest that technology and techniques
impossible to foresee now can lead to manipulation of the marine
environmeiit and the factors that influence population size of marine
fish. Some approaches have already been suggested. Certain diseases
of inshore species (such as Ichthyophonus disease of herring) might be
artificially supported at a level just high enough to maintain population
resistance at a point where epizootics would not occur. It might be
possible to overfish a population deliberately as soon as evidence of an
incipient epizootic is discovered. These methods are, of course, based
on present knowledge and do not constitute a legitimate portrayal of
future control based on the acquisition of new information.
The severe effects of epizootics on marine fish populations have
been partially documented for Ichthyophonus disease of herring, red
disease of eels and Pasteurella disease of white perch. Significant
reduction in population size was indicated in each outbreak by reduced
catches during the post-epizootic periods. It is tempting to speculate
on the basis of these observations that certain of the unexplained
major past fluctuations in abundance of commercial marine species
may have been caused by disease. As an example, drastic decline in
mackerel abundance on the Atlantic coast of North America in the
late nineteenth century may have been related t o disease. During the
1954-55 fungus-disease epizootic in herring of the Gulf of Saint
Lawrence, mackerel were found to be susceptible and heavily infected.
Mackerel landings in the southern Gulf declined at that time to half
their previous total, and have remained low to the present time.
Available catch records for mackerel of the western North Atlantic,
beginning in 1804, show periodic fluctuations which have been correlated with deviations in air temperatures by Taylor, Bigelow and
Graham (1957), but which may well have had more immediate causes,
such as periodic epizootics. It seems logical that wherever unexplained
catastrophic declines in a fishery have occurred, disease must be