40
CARL J. SINDERMANN
for example, found that exposures Lo low temperatures (0 to S O C )
during early incubation produced malformed larvae of bream, Abramis
ballerus L., and pike (probably Esox lucius L.). Sharp changes in
temperature during early development could also produce malformations or death. Physiological abnormalities in larvae are less easily
identified, except as they are reflected in lack of growth and death of
individuals.
V. EFBECTS OF DISEASE
The significance of marine fish diseases may be assessed from the
viewpoint of the host population or from that of the human predator.
Epizootics may reduce the numbers of fish available to man, and in a t
least some marine species disease may be a primary mechanism for
regulation of population size. Diseases that weaken or disorient fish,
or make them more conspicuous, can be of great importance in determining survival of individuals. Protozoan, helminth and copepod
parasites of the flesh, although not often direct causes of death, can
act to weaken or slow the host and are also of great economic significance in the landed catch.
A. Epizootics and mass mortalities
Mass mortalities of marine, estuarine and anadromous fishes are
common, even though many such events may escape scientific attention.
Newspapers and interviews with fishermen would probably provide
the best criteria for evaluating the extent of mortalities, except for
those events that occur beyond the continental shelves. Many factors
may, of course, contribute to mass deaths of marine fishes, including
physical and chemical changes in the environment (BrongersmaSanders, 1957), as well as the biological realities of starvation, predation
and disease. Disease is often suspect, but has infrequently been proved
without question to be a cause of mass mortalities. Too often scientific
study is not made, or is made too late, or the results of the study are
inconclusive. Interest in the event is usually proportional to the
numbers of fish dying a t the particular moment ; long-term studies
necessary to understand the role of suspected pathogens have rarely
been carried on.
The often dramatic increase in disease prevalence that we term an
epizootic is the result of interactions of such variables as susceptibility
of the host population, virulence and infectivity of the pathogen,
effectiveness of transmission and physical factors in the environment.
Fundamentally, an epizootic of an infectious disease requires that one
or more of the following conditions exist: (1) the pathogen must be
CARL J. SINDERMANN
for example, found that exposures Lo low temperatures (0 to S O C )
during early incubation produced malformed larvae of bream, Abramis
ballerus L., and pike (probably Esox lucius L.). Sharp changes in
temperature during early development could also produce malformations or death. Physiological abnormalities in larvae are less easily
identified, except as they are reflected in lack of growth and death of
individuals.
V. EFBECTS OF DISEASE
The significance of marine fish diseases may be assessed from the
viewpoint of the host population or from that of the human predator.
Epizootics may reduce the numbers of fish available to man, and in a t
least some marine species disease may be a primary mechanism for
regulation of population size. Diseases that weaken or disorient fish,
or make them more conspicuous, can be of great importance in determining survival of individuals. Protozoan, helminth and copepod
parasites of the flesh, although not often direct causes of death, can
act to weaken or slow the host and are also of great economic significance in the landed catch.
A. Epizootics and mass mortalities
Mass mortalities of marine, estuarine and anadromous fishes are
common, even though many such events may escape scientific attention.
Newspapers and interviews with fishermen would probably provide
the best criteria for evaluating the extent of mortalities, except for
those events that occur beyond the continental shelves. Many factors
may, of course, contribute to mass deaths of marine fishes, including
physical and chemical changes in the environment (BrongersmaSanders, 1957), as well as the biological realities of starvation, predation
and disease. Disease is often suspect, but has infrequently been proved
without question to be a cause of mass mortalities. Too often scientific
study is not made, or is made too late, or the results of the study are
inconclusive. Interest in the event is usually proportional to the
numbers of fish dying a t the particular moment ; long-term studies
necessary to understand the role of suspected pathogens have rarely
been carried on.
The often dramatic increase in disease prevalence that we term an
epizootic is the result of interactions of such variables as susceptibility
of the host population, virulence and infectivity of the pathogen,
effectiveness of transmission and physical factors in the environment.
Fundamentally, an epizootic of an infectious disease requires that one
or more of the following conditions exist: (1) the pathogen must be