field examination of fishes chapter 14. 14.2 routine examination- basic observations (cont.) sorted...
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Field Examination of Fishes
Chapter 14
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14.2 Routine Examination-Basic Observations (cont.)
• Sorted by species• Limit handling of live fish• Weights and measures
taken• Scales taken for age and
growth
Otolilth
Scale
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Basic Observations
• External sexing done (immature fish cannot be sexed externally)– Brighter coloration in males– Difference in genital opening– Difference in shape of head – Dissection can be used to
sex
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Analyses of diet
• Stomach content preservation
• Lavage...non lethal–Washing out of gut contents
• If small, entire specimen (fish) preserved
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Necropsy-Based Fish Health Assessment (cont.)
• Condition and organ indices– K or C- ratio of weight to the
cube of length• The higher, the plumper the fish
– Organosomatic indices- ratio of organ to entire body• Decrease in starved fish• Increase in fish subjected to toxins
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Necropsy-Based Fish Health Assessment (cont.)
– Hepasomatic index- liver weight/body weight
– Gonadosomatic index- ovary weight/body weight• Indicates time of spawning
• Condition and organ indices
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Necropsy-Based Fish Health Assessment
• Systematic condition assessment– Comparison with past
observations• Blood constituents
(hematocrit, leukocrit and plasma protein)
• State of maturity• Condition of gills,
pseudobranch, mesenteric fat, spleen etc
• Damage to extremities
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14.3 Emergency Examination
• Definition of Health and Illness in Wild Fishes:– Healthy fish may have pathogens or
stress– Diseased fish are affected to reduce
growth, slow reproduction, or die
• Refer to box 14.1 for list of Pathogen-Induced Fish Diseases
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Pathogens not the only cause of disease
• Degraded water quality
• Toxic pollutants
• Poor nutrition
• Overcrowding (encourages transmission of pathogens)
• Excessive competition
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Limitations of Field Diagnosis
• Health cannot be completely assessed through clinical signs
• Laboratory examination necessary
• Pathogen must be identified before positive diagnosis
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Investigations of Fish Kills
• Expertise in biology, chemistry, and statistics needed
• Requires immediate response
• Water samples inside and outside kill taken
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Investigations of Fish Kills
• Basic water quality characteristics measured on site
• Individual fish examined for ill health and frozen
• The cause of a kill is often not immediately known
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Data may be used in legal proceeding (cont.)
• Data should:– be well documented– not easily lost or altered
• Identify person responsible for each measurement
• Notes should be duplicated and stored separately from original
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• Photos and videos can be valuable
• Use "chain of custody" for samples
Data may be used in legal proceeding
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Primary role of fisheries biologist in fish kills
• Determine number, size and species killed
• Areal extent of kill
• Monetary value of fish killed
$$$
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Behavioral Signs
• "Piping" or gulping air at surface– response to low DO
• "Flashing" ... fish rubbing itself against the bottom
• Convulsions• Whirling
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External Signs (cont.)
• Body conformation and color– Excessive mucus
production on body and gills
– Fins clamped close to the body and shimmying
– Faded or blotchy coloration
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External Signs (cont.)
• Kill the fish in humane way– Is body shape
normal?– Protruding
eyeballs– Exopthalmia
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External Signs (cont.)
• Fins– Should be intact to the
end of the rays– Free of slime or
cottony fungus (Saprolegnia spp)
– No hemorrhagic areas
– Frayed fins (Flexibactor spp)
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External Signs (cont.)
• Skin, scales and mucus– Scales- lie flat and firmly
attached– Mucus- thin, clear and
evenly distributed – Surface- free of Reddened areas (Aeromonus spp), bloody sores, nodular growths, fungus
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External Signs
• Gills– To inspect gills, pull
operculum back– If freshly killed,
should be bright red, NO thick mucus covering
– Usual site for ectoparasites
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Internal Signs
• Technique for opening fish– Lay fish on side–Make incision above
vent, along rib cage– Scissors work best up
to 0.5 kg
• Check digestive tract, kidney, and muscle
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14.4 Sampling for Disease Organisms
• Diagnostic Expertise- important
• Should be sent to fish health expert
• Consult state fish and wildlife agency
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Sampling for parasites (cont.)
• Selection and care of specimens– Live fish mandatory for
parasite identification– Requires good
dissection microscope– Thorough examination
requires compound microscope
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Sampling for parasites
• Basic parasite examination– Kill the fish– Keep the surface moist– Remove the portions of fins and examine– Take mucus scrapings - examine under
compound microscope– Cut gill arch and examine – Dissect fish and examine internal organs
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Sampling for bacteria (cont)
• Selection and care of specimens– Fish must be alive
or freshly killed– If cannot be kept
alive, freeze in individual plastic bags
X
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Sampling for bacteria
• Bacterial indentification requires training
• Bacterial isolation fairly simple– see page 443 of
text for protocol
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Sampling Viruses
• Requires specialized procedures and equipment
• Select fish suspected of viral disease
• Transport to fish health laboratory
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14.5 Sampling Blood and Tissue
• Rationale for collection of blood and tissue samples– If no obvious
environmental stress factor
– No pathogens found– Useful for evaluation
of sublethal stress
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Sampling Blood (cont.)
• Techniques of obtaining blood– Tapping blood
vessels in hemal arch– If less than 15cm,
must be sacrificed– Larger than 15cm,
may use syringe on anesthetized fish
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Sampling Blood • Preservation of samples – Could be stored for several
hours– Hematocrit should be run
within minutes of blood collection
–Most blood characteristics determined from plasma• Centrifuge and separate
immediately
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Sampling for Histology (cont.)
• Postmortem changes histological features
• Samples have to be taken from fish collected alive
• Make small thin slices– Promote rapid penetration of fixative–Minimize concerns of inaccurate
artifacts
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Sampling for Histology
• Drop in labeled vials of fixative– Bouin's fluid excellent fixative– Ten per cent formalin– Volume of fixative should be 10 times
that of tissue
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Sampling for Residue Analysis• Tissue taken from any
fish that is not putrid• Heavy metal- store in
plastic• Organic compounds-
store in foil• Sample white muscle,
as is edible portion