Biological field and laboratory methods for measuring the quality of ...

4.0 SAMPLE ANALYSIS
4.1 Data Recording
The sample records should include collection
number, name of water body, date, locality, and
other pertinent information associated with the
sample. Make adequate field notes for each collection.
Write with water-proof ink and paper to
ensure a permanent record. Place the label inside
the container with the specimens and have the
label bear the same number or designation as the
field notes, including the locality, date, and collector's
name. Place a numbered tag on the outside
of the container to make it easier to find a
particular collection. Place any detailed observations
about a collection on the field data sheet.
Record fishery catch data in standard units such
as number or weight per area or unit of effort.
Use the metric system for length and weight
measurements.
4.2 Identification
Proper identification of fishes to species is important
in analysis of the data for water quality
interpretation. A list of regional and national
references for fish identification is located at the
end of this chapter. Assistance in confirming
questionable identification is available from
State, Federal, and university fishery scientists.
4.3 Age, Growth, and Condition
Changes in water quality can be detected by
studying the growth rate of fishes. Basic
methods used to determine the age and growth
of fish include:
• Study of fish length-frequencies, and
• Study of seasonal ring formations in hard
bony parts such as scales and bones.
The length-frequency method of age determination
depends on the fact that fish size varies
with age. When the number of fish per length
interval is plotted on graph paper, peaks generally
appear for each age group. This method
works best for young fish.
The seasonal ring-formation method depends
on the fact that fish are cold-blooded animals
and the rates of their body processes are affected
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FISH IDENTIFICATION
by the temperature of the water in which they
live. Growth is rapid during the warm season and
slows greatly or stops in winter. This seasonal
change in growth rate of fishes is often reflected
in zones or bands (annual rings) in hard bony
structures, such as scales, otoliths (ear stone),
and vertebrae. The scales of fish may indicate
exposure to adverse conditions such as injury,
poor food supply, disease, and possibly water
quality.
Note the general well being of the fish - do
they appear emaciated? diseased from fungus?
have open sores, ulcers, or fin rot? parasitized?
Check the gill condition, also. Healthy fish will
be active when handled, reasonably plump, and
not diseased. Dissect a few specimens and check
the internal organs for disease or parasites. The
stomachs can be checked at this time to determine
if the fish are actively feeding.
5.0 SPECIAL TECHNIQUES
5.1 Flesh Tainting
Sublethal concentrations of chemicals, such as
phenols, benzene, oil, 2, 4-D, are often responsible
for imparting an unpleasant taste to fish
flesh, even when present in very low concentrations.
Flesh tainting is nearly as detrimental to
the fisheries as a complete kill.
A method has been developed (Thomas,
1969) in which untainted fish are placed in cages
upstream and downstream from suspected waste
sources. This procedure will successfully relate
the unacceptable flavor produced in native fish
if exposed to a particular waste source.
To ensure uniform taste quality before exposure,
all fish are held in pollution-free water for
a IO-day period. After this period, a minimum
of three fish are cleaned and frozen with dry ice
as control fish. Test fish are then transferred to
the test sites, and a minimum of three fish are
placed in each portable cage. The cages are suspended
at a depth of 0.6 meter for 48 to 96
hours.
After exposure, the fish are dressed, frozen on
dry ice, and stored to OaF until tested. The control
and exposed samples are shipped to a fishtasting
panel, such as is available at the food
science and technology departments in many of