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

BIOLOGICAL METHODS
technique, or combination of techniques, will
completely sort out or make more readily
discernible all types of organisms from all types
of substrate material. In the end, the total
sample must be examined. If technicians are
routinely conducting the picking operation,
these techniques may lead to overconfidence
and careless examination of the remainder of the
sample. If used with proper care, such aids are
not objectionable; however, they are not recommended
as standard techniques.
As organisms are picked from the de bris, they
should be sorted into major categories (i.e.,
insect orders, molluscs, worms, etc.) and placed
into vials containing 70 percent ethanol. All vials
from a sample should be labeled internally with
the picker's name and the lot number and kept
as a unit in a suitable container until the
organisms are identified and enumerated, and
the data are recorded on the bench sheets. A
typical laboratory bench sheet for fresh-water
samples is shown in the Appendix.
4.5 Identification
The taxonomic level to which animals are
identified depends on the needs, experience, and
available resources. However, the taxonomic
level to which identifications are carried in each
major group should be constant throughout a
given study. The accuracy of identification will
depend greatly on the availability of taxonomic
literature. A laboratory library of basic
taxonomic references is essential. Many of the
basic references that should be available in a
tenthos laboratory are listed at the end of the
chapter.
For comparative purposes and quality control
checks, store identified specimens in a reference
collection. Most identifications to order and
family can be made under a stereoscopic
microscope (up to SOX magnification). Identification
to genus and species often requires a compound
microscope, preferably equipped with
phase contrast (la, 45, and lOOX objectives) or
Nomarski (interference phase) optics.
To make species identifications, it is often
necessary to mount the entire organism or parts
14
thereof on glass slides for examination at high
magnification. Small whole insects or parts
thereof may be slide-mounted directly from
water or 70 percent ethanol preservative if CMC
mounting media is used. Label the slides
immediately with the sample log number and
the name of the structure mounted. Euparol
mounting medium may be preferable to CMC
for mounts to be kept in a reference collection.
Place specimens to be mounted in Euparol in
95 percent ethanol before mounting.
To clear opaque tissue, heat (do not boil) in a
small crucible (5-ml capacity) containing 5 to 10
percent KOH solution (by weight) until it
becomes transparent. The tissue can be checked
periodically under a stereoscopic microscope to
determine if it is sufficiently cleared. Then transfer
the tissue stepwise to distilled water and 95
percent ethanol for 1 minute each and mount
with CMC or Euparol. Several different
structures can be heated simultaneously, but do
not reuse the KOH solution.
The above methods work well for clearing and
mounting midges, parts of caddisflies, mayflies,
stoneflies, other insects, crustaceans, and
molluscs; however, worms, leeches, and turbellarians
require more specialized treatment before
mounting (la, 47).
Larval insects often comprise the majority of
macroinvertebrates collected in artificial
substrate samplers and bottom samples. In
certain cases, identifications are facilitated if
exuviae, pupae, and adults are available. Collect
exuviae of insects with drift nets or by skimming
the water's surface with a small dip net near the
shore. Obtain adults with sweep nets and tent
traps in the field or rear larvae t9 maturity in the
laboratory.
The life history stages of an insect can be
positively associated only if specimens are reared
individually. Rear small larvae individually in 6to
12-dram vials half filled with stream water
and aerated with the use of a fine-drawn glass
tubing. Mass rearing can be carried out by
placing the larvae with sticks and rocks in an
aerated aquarium. Use a magnetic stirrer inside
of the aquarium (41) to provide a current.