To Eat or Not to Eat

            Hello all I am very excited to introduce you all to prey capture in electric fish and how climate change may affect identification and response time when capturing prey.  Many species of both strong and weakly electric fish relay on their electric organ to communicate to conspecifics to locate prey. However, challenges may arise when signals of what the electric fish may think of being prey is a predator (Milam et al. 2019).  In the last post, on communication we spoke about how electric fish can discern between multiple signals.

           A study by MacIver and colleagues investigated prey capture in Gymnotid fishes and how water conductivity may influence their forging behavior (MacIver et al. 2001). Electric fish utilize high and low electric frequencies to find prey items.  In ghost knifefish they usually are locating small insects and crustaceans(MacIver et al. 2001). These small prey items produce a large signal because of the difference in the impedance of the organism to the surrounding water (MacIver et al. 2001). From my limited knowledge of Physics, an electrical impedance can be thought of as the resistance in a closed circuit; this means that the muscle of the organism produces a much larger impedance than the impedance of the water which produces a high current (Hyperphysics 2019). This fact may be important when investigating the effects of climate change on prey capture in electric fish, because the conductivity of the water may decrease which would therefore decrease the impedance between the organism and the water.

           Electric fish tend to show a C-start behavior when trying to capture prey (MacIver et al. 2001). This behavior can be characterized by an initial velocity then a quick stop and turning of the body. This behavior is typically done in prey animals to avoid predation. The C-start behavior has been determined to start from a two, large, neuron in the hindbrain called a mauthner cell (Machnik et al. 2018).  In the MacIver study the electric fish detected the prey from the dorsal side of their body with having a successful (for the electric fish) interaction 97% of the time (MacIver et al. 2001).  Electric fish also exhibit a body roll behavior that orientates prey to the dorsum of the electric fish.  It is not a coincidence that this position has a higher success when capturing prey
(Maclver et al. 2001).

Small weakly electric fish
Carl Hopkins, ElectricFish, CC BY-SA 3.0

           One of the many questions I had about electric fish prey capture is how they were able to differentiate between different objects that give out an electrical impulse.  It turns out that they can differentiate by tuning neural signals sort of make a shape out of what they are picking up (Charcron et al. 2005). 

          Electric fish posses many adapted abilities to locate prey however, it may become more difficult for them to successfully perform these tasks due to the changing climate. Because any change in the environment can compromise the electric organ.

Electric Eel
Steven G. JohnsonElectric-eel2CC BY-SA 3.0

Literature Cited:

1. Chacron MJ, Maler L, Bastian J. Electroreceptor neuron dynamics shape information transmission. Nature Neuroscience. 2005;8(5):673–678. doi:10.1038/nn1433

2. Impedance. [accessed 2019 May 8].

3. Machnik P, Leupolz K, Feyl S, Schulze W, Schuster S. The Mauthner cell in a fish with top-performance and yet flexibly tuned C-starts. II. Physiology. The Journal of Experimental Biology. 2018;221(13):jeb175588. doi:10.1242/jeb.175588

4. MacIver MA, Sharabash NM, Nelson ME. Prey-capture behavior in electric fish. :15.

5. Milam OE, Ramachandra KL, Marsat G. Behavioral and neural aspects of the spatial processing of conspecifics signals in the electrosensory system. Behavioral Neuroscience. 2019 May 2 [accessed 2019 May 8]. doi:10.1037/bne0000320

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