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Abstract(s)
Although sound production in teleost fish is often associated with territorial
behaviour, little is known of fish acoustic behaviour in other agonistic contexts
such as competitive feeding and how it changes during ontogeny. The grey
gurnard, Eutrigla gurnardus, frequently emits knock and grunt sounds during
competitive feeding and seems to adopt both contest and scramble tactics under
defensible resource conditions. Here we examine, for the first time, the effect of
fish size on sound production and agonistic behaviour during competitive feeding.
We have made sound (alone) and video (synchronized image and sound)
recordings of grey gurnards during competitive feeding interactions. Experimental
fish ranged from small juveniles to large adults and were grouped in four size
classes: 10–15, 15–20, 25–30 and 30–40 cm in total length. We show that, in this
species, both sound production and feeding behaviour change with fish size.
Sound production rate decreased in larger fish. Sound duration, pulse duration
and the number of pulses increased whereas the peak frequency decreased with
fish size, in both sound types (knocks and grunts). Interaction rate and the
frequency of agonistic behaviour decreased with increasing fish size during
competitive feeding sessions. The proportion of feeding interactions accompanied
by sound production was similar in all size classes. However, the proportion of
interactions accompanied by knocks (less aggressive sounds) and by grunts (more
aggressive) increased and decreased with fish size, respectively. Taken together,
these results suggest that smaller grey gurnards compete for food by contest
tactics whereas larger specimens predominantly scramble for food, probably
because body size gives an advantage in locating, capturing and handling prey.
We further suggest that sounds emitted during feeding may potentially give
information on the motivation and ability of the individual to compete for food
resources.
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Citation
Ethology, 111, 256-269