Animations & Cartoons

As scientists and educators, it is our responsibility to share scientific information and engage with audiences beyond academia. This is critical for the society.

About electric fishes

Diana Marques created the animation for the electric fish exhibit at the National Zoological Park under my supervision.

What are South American Electric Fishes?
This group consists of over 250 species of freshwater fish in the order Gymnotiformes. They possess at least one electric organ that allows them to generate their electric field, which is represented by the orange line along the body in Animations 1 and 2.

How is the electric discharge generated?
The electric organs consist of modified muscle or nerve cells called electrocytes. These cells receive synchronized signals from the brain to fire, and when they do, they act like serially connected batteries with asymmetric polarization. Weak electric organ discharges (EODs) are categorized into two types: pulse and wave.

Can electric fish give you an electric shock?
Most of them can't! The majority of the electric fish species only produce weak EODs (ranging up to 2300Hz). It is used for navigation and communication. In addition to weak EODs, the electric eels (genus Electrophorus) generate strong EODs up to 860V for hunting and self-defense (Animation 3).

Animation 1: Pulses EODs are brief all-or-none events of the order of 1 ms or a few milliseconds separated by much longer intervals (orange graphic in the bottom). Heard in a speaker (turn speakers on!), a buzzing sound or single clicks at very low discharge rates are heard. For example, in species of banded bluntnose electric knifefishes (genus Steatogenys).

Animation 2: Wave EODs have no pauses between them. Thus that they represent a continuous wave and are of a constant frequency that may be modulated when the fish is excited (orange graphic at the bottom). Heard in a speaker (turn speakers on!), wave EODs sound like a musical instrument playing a constant tone. For example, in species of glass electric knifefishes (genus Eigenmannia).

Animation 3: Electric eels possess three electric organs: Main, Hunter’s, and Sachs'. Main and Hunter’s electric organs produce high-voltage electric organ discharges (used for self-defense and predation) and Sachs' generates the low-voltage EODs (pulse EODs used for navigation and communication). Nonetheless, all three electric organs fire during the high-voltage EODs. Electric organs are composed by thousands of electrocytes organized as batteries in series. Electrocytes when at rest, have a negative ion charge inside (relative to the positive ion outside) and therefore a charge of 0 mV. However, when activated (by the motor neuron activities) the positive ions flow inside the electrocyte, causing a potential reverse of c. 150mV. So, when the electrocytes are excited at the same time they produce voltages up to 860 V.

Fed in a speaker, electric eel pulse EODs are single clicks that can be slow (eel resting or swimming slowly) or fast (eel swimming fast) depending on the fish's activity