2. Behavioral Biology TALKS - Deutsche Zoologische Gesellschaft

esults imply that instead of using only single electrical ‘snapshots’ of an object, fish
have to make use of temporal modulations of a series of electric images caused by
movement to reliably detect object shape.
����12 Michael Blum
The electric eel economizes on its electric organ discharges, required to paralyze
prey until it is swallowed up
Authors: Michael Blum 1 , Stefan Schuster 1 , Wolfram Schulze 1 , Peter Machnik 1
Affiliation: 1 Department of Animal Physiology, Bayreuth
The electric eel (Electrophorus electricus) is well known for its ability to generate
strong Electric Organ Discharges (EODs) for self-defense and hunting. The electric eel
is an obligate mouth breather and dies when access to water surface is denied.
Accordingly its mouth mucosa is extremely thin and strong supplied with blood, so it
is sensitive and susceptible to injury. To minimize this risk, Electrophorus electricus
paralyzes its prey with strong EODs. It seems reasonable to think that the shocks are
maintained as long as the prey is swallowed up, perhaps as a simple reflex that
generates EODs while prey is in its mouth.
Here we show, that Electrophorus electricus just uses its strong EODs until the prey is
paralyzed, then it switches them off and just restarts pulsing if the prey starts moving
again. So the strong EODs are just used when required.
The obvious benefit of this tactic is that the electric eel is able to conserve energy.
Furthermore there is another advantage. While the prey is getting shocked, its
muscles contract thus fins erect, which could hurt the highly sensitive mouth cavity,
especially if the prey has fin rays. So, its economic discharging behavior also keeps
Electrophorus electricus from worrying about, if prey has fin rays or not.
����13 Sabine Feyl
Orientation in electric fields: More than line-following in electrosensory predators?
Authors: Sabine Feyl 1 , Peter Machnik 1 , Wolfram Schulze 1 , Stefan Schuster 1
Affiliation: 1 Department of Animal Physiology, University of Bayreuth
In contrast to almost all other sensory systems the electrical sense does not seem to
allow easy localisation of the sender. A number of thorough studies have convincingly
shown that territorial electric fish approach discharging conspecifics by following the
current lines and initially without knowing distance and direction to the source of the
discharges.
This strategy is safe but useless when the sender deactivates its discharges and it
requires more time than a direct approach. Both may be important in a hunting
context. According to this we asked if the ability to localise sender position efficiently
is better developed in fish that hunt on the basis of electric signals. Such a situation is
known for the electric eel Electrophorus electricus that preys on the weakly electric
fish Gymnotus carapo. By mimicking the discharges of Gymnotus we analyse if
Electrophorus can take a direct approach to the sender and detect it even when it
goes silent.
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