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17.4.2 Activityoforganismsasstress indicator
2008). Moreover, for ecotoxicological purposes, IA may
help to interpret behaviour patterns. Juchelka and Snell
(1994) reported the effects of several types of toxicants
on rotifer ingestion rate, by quantifying gut fluorescence
(in this experiment, rotifers ingested fluorescently labeled
latex spheres).
IA may also provide adequate tools to quantify motil-
ity of organisms, which is currently the most studied
activity pattern for detecting various types of stress. The
ability of the unicellular flagellate
Euglena gracilis
to ori-
ente in the gravity field, its mobility and velocity were
found to be sensitive to a number of toxic compounds.
Therefore, a warning system for monitoring the quality
of water has been developed using a real time IA sys-
tem which quantified the movement parameters of this
species (Tahedl and Hader, 1999). The software used the
vectors of the tracks to calculate the number of motile
cells, the percentage of cells moving upwards, their mean
velocity and their precise orientation. Statistically sig-
nificant changes in the parameters indicated variability
in water quality, even over very short time periods. In
similar studies, Unterstainer et al. (2003) showed that,
after only 9 h of high copper exposure, a significant
decrease of the average swimming velocity of
D. magna
was observed. In their experiment, they recorded the co-
ordinates of daphnids from two frames and automatically
reconstructed their trajectories. Lee et al. (2005) showed
that individual medaka fish (
Oryzias latipes
), affected
by diazinon (an insecticide) were less active, and their
movement behaviour was more erratic than that of unaf-
fected/control specimens. Finally, note that motility of
gametes (a task that will not be developed here) may also
help to assess, among other things, the potential haz-
ards of environmental pollutants on reproduction (see
a review in Kime et al., 2001, and further developments
for fish in Van Look and Kime, 2003 and Marco-Jimenez
et al., 2006).
Bacteria play an important part in the functioning of
aquatic ecosystems (e. g. crucial link in food webs, carbon
cycling and degradation of heavy metals), and imagery
methods for detecting physiologically active bacteria in
natural microbial communities have been developed.
Ogawa et al. (2003) presented a simple multicolor digital
IA system, which differentiated between actively respiring
bacteria and non-respiring bacteria based on distinc-
tive color information using epifluorescence microscopic
images. They also developed an algorithm to distinguish
bacteria from detritus based on color segmentation, which
produced bright fluorescence in different colors. Utilis-
ing a similar approach, a two-dye fluorescence bacterial
viability kit rapidly distinguished between live and dead
bacterial cells (Amalfitano et al., 2008).
Phosphorus concentrations, the main nutrient
responsible for eutrophication, can be assessed indirectly
by estimating the activity of various organisms. Using the
'easy image analyzer 2000 software', Kragh et al. (2008)
analysed freshwater bacterial abundance, biovolume and
growth efficiency. They were able to demonstrate exper-
imentally that the availability of phosphorus has major
implications in growing processes and, subsequently, for
the quantitative transfer of carbon in microbial food webs.
The regulated phosphatise activity of several phytoplank-
ton species, based on external phosphorus concentration,
were also demonstrated by fluorescence quantification
(enzyme-labelled fluorescence technique) ( Strojsov a
et al., 2005). From fluorescence microscopy coupled with
IA, Znachor and Nedoma (2008) quantified silicon (Si)
deposition over time and distinguished between diatom
cells that were actively depositing Si and those that were
not. They showed that, at the water surface, silica depo-
sition by diatoms was limited by phosphorus deficiency.
Burbank and Snell (1994) developed biomarkers of
sublethal toxicity in the freshwater rotifer
Brachionus
calyciflorus
based on the reduction of enzyme activity.
Esterase and phospholipase A2 activity was quantified in
single rotifers using IA and a fluorescence detection sys-
tem. Quantification of enzyme activity demonstrated that
toxic stress reduced rotifer activity in a dose-dependent
manner. Johnson and Delaney (1998) showed that growth
of the waterflea
Daphnia magna
may be a useful short-
term (7 day) indicator of chronic toxicity (i.e. zinc and
3,4-dichloroaniline exposure) based on the body length
measured on day 0, 2, 4, and 7 using an IA method.
Population growth rate (PGR) of
D. magna
can also be
used to estimate environment suitability (Hooper et al.,
17.4.3 Fluctuatingasymmetryasstress indicator
Fluctuating asymmetry of bilateral traits (FA) refers to a
population-level pattern of slight bilateral morphometric
asymmetries observed in individuals, with no consistent
directional pattern being observed in the population as
a whole. Although a low FA is not the
'unambiguous
measure of well being and good genes that has been claimed'
(Rasmuson, 2002), FA can increase under various stress
conditions and, subsequently, is a potential indicator of
past and present factors of stress. Servia et al. (2004)
measured FA levels in various structures of the head
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