DISEASES OF MARINE FISHES
63
Another critical question concerns the effects of disease on the
very early life history stages of fishes. It is generally accepted that
much of the mortality of a given year class occurs in the embryonic
and larval stages. Variables such as oxygen. temperature, salinity and
food supply are undoubtedly important, as is the very obvious and
extensive predation on eggs and larvae. Effects of disease, which niay
also be significant, are less clearly understood, but are amenable to
descriptive and experimental studies.
Another research area deserving greater attention concerns the
role of viruses and bacteria in marine fish populations. Enough
evidence is already available to prove that bacteria can be significant
primary or secondary invaders, and causes of mortality in natural as
well as captive populations. Identification of bacterial pat hogens is
not simple ; the classification is at present confused ; reinfection from
cultured organisms is often unsuccessful ; and disease-free experimental
fish that have not been exposed in the past to the same or related
organisms may be very difficult to obtain. Other basic and related
problems immediately present themselves-such as the role of marine
bacteriophages in populations of bacteria potentially pathogenic to
fish (Spencer, 1963), and the role of antibiotics elaborated by many
marine organisms in suppressing bacterial populations (Lucas. 19.55 ;
Nielsen, 1955). Knowledge of viruses as pathogens of marine fishes is
even more rudimentary than is that for bacteria, except for tumorinducing agents. Currently available established cell cultures of
marine fish origin should do much to improve our understaiding of
viruses in the oceans.
XI. SUMMARY
Diseases of marine fishes are less well known than those of freshwater species because :
( a ) Mortalities and epizootics in the sea are so much less apparent
and less frequently observed than are those in the more restricted
fresh-water habitat, that the true role of disease in the sea has not
been fully appreciated.
( b ) Fresh-water hatcheries and aquaria are much more numerous
than comparable salt-water facilities.
Problems associated with
crowding, artificial feeding and disease control for salt-water species
have not had to be confronted with the same intensity of research as
for fresh-water species. Much of the impetus for research and the
advances in understanding of disease in fresh-water fishes have
originated in the hatchery or aquarium environment ; this impetus
has been largely lacking for marine species.
63
Another critical question concerns the effects of disease on the
very early life history stages of fishes. It is generally accepted that
much of the mortality of a given year class occurs in the embryonic
and larval stages. Variables such as oxygen. temperature, salinity and
food supply are undoubtedly important, as is the very obvious and
extensive predation on eggs and larvae. Effects of disease, which niay
also be significant, are less clearly understood, but are amenable to
descriptive and experimental studies.
Another research area deserving greater attention concerns the
role of viruses and bacteria in marine fish populations. Enough
evidence is already available to prove that bacteria can be significant
primary or secondary invaders, and causes of mortality in natural as
well as captive populations. Identification of bacterial pat hogens is
not simple ; the classification is at present confused ; reinfection from
cultured organisms is often unsuccessful ; and disease-free experimental
fish that have not been exposed in the past to the same or related
organisms may be very difficult to obtain. Other basic and related
problems immediately present themselves-such as the role of marine
bacteriophages in populations of bacteria potentially pathogenic to
fish (Spencer, 1963), and the role of antibiotics elaborated by many
marine organisms in suppressing bacterial populations (Lucas. 19.55 ;
Nielsen, 1955). Knowledge of viruses as pathogens of marine fishes is
even more rudimentary than is that for bacteria, except for tumorinducing agents. Currently available established cell cultures of
marine fish origin should do much to improve our understaiding of
viruses in the oceans.
XI. SUMMARY
Diseases of marine fishes are less well known than those of freshwater species because :
( a ) Mortalities and epizootics in the sea are so much less apparent
and less frequently observed than are those in the more restricted
fresh-water habitat, that the true role of disease in the sea has not
been fully appreciated.
( b ) Fresh-water hatcheries and aquaria are much more numerous
than comparable salt-water facilities.
Problems associated with
crowding, artificial feeding and disease control for salt-water species
have not had to be confronted with the same intensity of research as
for fresh-water species. Much of the impetus for research and the
advances in understanding of disease in fresh-water fishes have
originated in the hatchery or aquarium environment ; this impetus
has been largely lacking for marine species.