Locomotion and Behavioral Toxicity in Larval Zebrafish: Background, Methods, and Data - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 151

Figure 12.2 Effect of lighting conditions on activity. Larvae (n¼164) were tested under alternating
10min periods of light and dark. The bar in the lower portion of the figure denotes lighting condition.
Activity is presented as unfiltered and filtered data; filtering (see the text for details) eliminated minor
movements that did not qualify as locomotion to a trained observer. Each point represents meanSEM
distance moved in 2min. Filtering the data reduced the magnitude of activity, but did not distort the pattern
of activity over time or lighting condition.
well. For this reason, a sampling rate of 200ms and a minimumdistance of 0.135 cm
were used to measure locomotion, which agreed with visual observation of the
larvae. The data collected with this constraint can therefore be technically referred
to as filtered data. Figure 12.2 shows a close correspondence between filtered and
unfiltered data, although filtering results in lower activity as expected. While
Fig. 12.2 indicates that similar results can be obtained regardless of filtering, it
is likely that some chemical exposures could produce divergent results owing to
minute displacements similar to those produced by tremor or shaking in studies on
locomotor activity in rodents.
An obvious question concerned the importance of the length of the light and dark
periods. The results of these experiments have been published (MacPhail et al., 2009).
In brief, duration of the initial dark period (either 10 or 20min) had no effect on either
the level of activity in subsequent light or the increase in activity when the larvaewere
returned to dark. Duration of the light period did, however, affect subsequent dark
activity, being higher following 15min of light than following 5min of light.
Given the substantial effect on activity of switching between light and dark,
especially the rapid initial activity decrease in light, further studies investigated the
influence of light intensity on locomotion. Accordingly, the apparatus was modified
electronically to allow manipulation of light intensity over a broad range of values.
Figure 12.3 shows the results of one experiment. The bright light level is the same as
used in the experiments described above, while the lower intensity is noticeably dim to
an observer. Under both lighting conditions, activity increased to an equivalent stable
level, although that level was reached faster at the lower intensity. In addition, the