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Fig. 2. Rectified electromyograms representing typical raw data from feeding
behaviours in O. mykiss (left) and S. jardinii (right). Data
for five sampled muscles are shown: SH, sternohyoideus; PH, protractor
hyoideus; AM, adductor mandibularis; EP, epaxialis; HP, hypaxialis. Measured
variables are indicated with brackets: a, activity onset time, relative to EP
activity onset (vertical dotted lines); b, activity duration; c, activity mean
amplitude [in analyses corrected with highest muscle-specific amplitude
(spike) during an experiment]; d, integrated area, an intensity measurement of
the area defined by the rectified curve and the baseline of the muscle
activity signal (grey shading). In O. mykiss, SH dist. is
sonomicrometry data on strain, measured with two piezoelectric electrodes
sutured to the ventral coracoid and urohyal keels, at the sternohyoideus
origin and insertion. Note that in some rakes (rake 1) SH activity does not
equal contraction and SH stretching results from HP or PH activity. In other
rakes, exhibiting greater SH activity (rake 2), the initial stretching is
compensated for by much higher levels of SH activity. In S. jardinii,
isolated chewing behaviour is uncommon and not illustrated, whereas raking is
preceded by muscle activity driving a ubiquitous prey repositioning behaviour
with EMG profiles closely resembling chewing EMG profiles (see O.
mykiss). We only analysed raking EMG data that were clearly distinguished
from this early behaviour (by at least 50 ms pause in activity for all
muscles; rake A). Less discreet behaviour complexes (rake B) were omitted from
analysis.
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