Nonetheless, viruses like Salmon Anemia Virus cause million

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Fish diseases and the
environment Paul R. Earl and Arcadio Váldez
González Facultad de Ciencias
Biológicas Universidad Autónoma de Nuevo
León San Nicolás, NL 66451
pearl_at_dsi.uanl.mx
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Healthy fishes are compromised by unfavorable
changes in their habitatThe major feature of
the epidemiology of fishes is the rise of the
proverbial opportunistic pathogen. Fishes are
normal in healthful environments, and this is
obvious. The same fishes and the waters they live
in usually carry the same microorganisms, many of
which are opportunistic pathogens. Overcrowding
leading to disease is quite likely in commercial
ponds of fishes.
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Overcrowding with low oxygen and high secreted
ammonia is the major cause of disease, and
ciliated protozoa can be leading pathogens as
aeromonads and other bacteria might be. Viruses
are much less often causes of disease.
Nonetheless, viruses like Salmon Anemia Virus
cause millions of dollars of quick losses without
considerations of environmental deterioration.
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Billions of humans demand more and more
nitrogen-based fertilizer to make food. Some
consequences are 1. elevated CO2, 2. climate
change via greenhouse gases, 3. land-use
change, 4. loss of biodiversity, 5. biological
invasions, and 6.
increased N fixation. Human activities are
having global consequences.Nitrogen and other
gases of the global warming trend are poorly
studied in regard to fishes. Nearly one third of
the Earth's land surface is devoted to raising
crops and domestic animals. Large areas of
diverse natural vegetation with soybeans, peas,
alfalfa and other leguminous crops have changed
the environment. The burning of fossil fuels such
as coal and oil releases previously fixed
nitrogen, causing the further escalation of
atmospheric nitrogen.
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The waters of some streams and lakes are also
being acidified by industrial pollutants like
sulfides. Excess nitrogen is being transported by
rivers into estuaries and coastal waters. Has
this unprecedented nitrogen loading contributed
to long-term declines in coastal fisheries and
accelerated losses of biological diversity in
both aquatic and land-based ecosystems?Overextrac
tion of freshwater by pumping in many places can
lead to salination, and the invasion of salt
tolerant fishes as in the Rio Grande. Pollution
and overextraction of freshwater are foremost
problems and relate to human overpopulation.
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References for fish healthThe purpose of this
lecture with its Spanish version is to acquaint
you with fish diseases (fds), assuming you are
interested in fresh or saltwater fishes as food,
sport or in decorative aquaria. As a scientific
field of interest fds are poorly developed,
lacking organization and cohesiveness.
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More literature on the
netSouthern Regional Aquaculture Center (SRAC),
the University of Florida (UF) and the
University of Texas (TAMU) are congratulated for
their excellent contributions to fish
health.SRAC 4700, Saprolegniasis (winter
fungus) and Branchiomycosis
of Commercially Cultured Channel
CatfishSRAC 472, Submitting a Sample for Fish
Kill Investigation SRAC 473, Medicated Feed
for Food FishSRAC 474, The Role of Stress in
Fish DiseasesSRAC 475, Proliferative Gill
Disease (Hamburger Gill Disease)SRAC 476, Ich
(White Spot Disease) SRAC 477, ESCEnteric
Septicemia of CatfishSRAC 478,Aeromonas
Bacterial Infections-Motile Aeromonad
SepticemiaSRAC 479B, Columnaris Disease
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NutritionWide ranging
fishes can choose a balanced diet, whereas
confined fishes cannot. Complete rations
sometimes called aquafeed must be formulated to
meet all nutritional requirements. About 3,500
kilocalories per kg of diet with 100 mg protein
daily is also needed.Minerals and vitamins are
of course needed. The growth should be 2 times
the ration per kg of gain. Blood hemoglobin is 10
g/dL, hematocrit 32 . The erythrocyte count is 1
million per cm of blood.
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Aquaculture and moreGlobal
production of farmed fishes and clams has more
than doubled during the past 25 years, growing
from 10 million metric or megatons (mt) to over
29 mt at the turn of the century. Meanwhile,
harvests of ocean fishes have remained at around
90 mt. Regardless, wild fish stocks are
overfished. Today aquaculture the farming of
fish, shrimp, clams and oysters supplies more
than one-fourth of all commercial fishes. A
kilogram of the high-market-value species like
salmon can cost 3 kg of cheap fishes.
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Between 1986-97, 4 of the top 5, and 8 of the top
20 wild species harvested from the ocean were
small fishes used in production of animal feed
anchoveta, Chilean jack mackerel, Atlantic
herring, chub mackerel, Japanese anchovy, round
sardinella, Atlantic mackerel and European
anchovy.As aquaculture production continues to
increase and intensify, both its reliance and
impact on ocean fisheries are likely to expand
even further. The future balance between farmed
and wild-caught fish, the total supply of fish
available for human consumption, and the health
of the marine environment will depend on trends
in aquaculture practices.
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Deterioration of the environment and
toxicityDifferent fishes live in a) fresh, b)
brackish and c) saltwater. Seawater can have
salts at g/L as NaCl 28.014 MgCl2
3.812 MgSO4 1.752 CaSO4 1.283 K2SO4
0.816 CaCO3 0.122 KBr 0.101 SrSO4 0.028
H2BO3 0.028
as 3.5 NaCl.
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Fish killsTypical
questions on a fish kill are Where and when
was the fish kill discovered? Size and depth of
the pond? Source of water? What is the water
temperature? What type and how many aquatic
plants? Any recent agricultural spraying or
animal waste runoff? Any recent thunderstorm or
hot, cloudy weather? What species of fish were
killed? Was just one species of fish killed?
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A simple explanation of a fish killThe 100
disaster was likely due to the shortage of
oxygen. A fish kill can occur in fresh, brackish
or saltwater. The degradation of domestic waste
absorbs oxygen and promotes nitrite that uses
oxygen to go to nitrate. Algae and protozoan
dinoflagellates bloom enormously. A marine fish
kill happens at the shore.In sunlight,
microorganisms produce oxygen. At night, this
plankton community uses it.You can see what will
happen to the fishes and invertebrates in the
early morning hours,More than one million
fishes, primarily menhaden, were reported killed
on August 20, 2003 in Narragansett bay, Rhode
Island, USA. A fish kill of this magnitude
demonstrates the fragility of the environment.
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Organic wastes, nitrogen and acid lakes
Coal-fired electric utility plants are the major
source of pollution in the US, especially via the
production of acid rain. Coal is of course the
major competitor of oil.Our culture depends upon
burning fossil fuels.Also nitrogen, relating to
food demand, increases and supports the global
warming trend. Aquaculture and overfishing are
merely the RESULTS of social changes, including
human overpopulation. However, the invention of
ammonia production by Fritz Haber (1868-1934) for
fertilizers solved the food shortage problem as
visualized by Malthus (1766-1834). About 1900,
the human population skyrocketed and so did
nitrogen production thanks to the Haber process.
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Pesticide toxicityMany
of these compounds are anti-enzymes. For
instance, mammals and fishes do not have the same
enzymes that the invertebrate pests have. Lack
of specificity is the main fault of the
disinfectants formalin, copper sulfate, potassium
manganate and outcompetimg introduced rainbow
trout rotenone might be used to eliminate all
fishes, and trout reintroduced over a year later.
Abate?
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Immune responseFishes do
not have lymph nodes and do not produce gamma
globulin. Otherwise, they are rather similar to
mammals. B T lymphocytes are seen. Vibrio spp.
and other bacterins have been commercially
introduced. However, research in vaccines is far
behind what it might be and this implies lack of
incentive. One successful example is given. The
disease ich or white spot can be controled by
injecting vaccine of ground Ichthyophthirius
multifilis. ALSO ! cilia from related Tetrahymena
thermophia (T.
pryriformis) give protection. By 3 weeks,
injected or bathed fish were protected. Still,
protection duration is merely guesswork.
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Cancer Some fishes,
particularly bottom-feeding ones, develop
papillomas on the skin, lips, opercula and fins.
These growths are infections caused by viruses
that are sometimes intimately associated with
carcinomas in man, i. e., papilloma viruses.
Regardless, cancers (tumors) like visceral
granuloma and fibromas and other neoplasms
(cancers !) are rare in fishes, possibly because
they don't live long enough.
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Endangered speciesHealthy fishes
are of course compatible with their environment.
Fishes fill a given niche within ecological
limits. Pollution diminishes their survival.
Diseases can be approached with concern for
physical factors like osmotic pressure,
temperature, pH and oxygen saturation that are
often neglected. The viability of fish eggs is
still another inquiry.
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The world fisheries are not sustainable.Large
marine sanctuaries have been suggested. Georges
banks at northeastern USA near the Canadian Grand
banks has been closed for several years, because
of depleted stocks of cod, haddock and flounder.
Herring mackerel have rebounded in 10 years.
However, the species composition changed ! Will
herring mackerel now compete strongly with cod
and other large fishes ? The food chain has
changed.