Finally the grim weather gripping the UK has finally begun to lift just in time for the spring field surveying season. This week we trade in the toxins of the Koppie Foam Grasshopper for an electrical issue. Hope you guys enjoy.
Issue #112 – Electric Eel
Kingdom – Animalia
Phylum – Chordata
Class – Actinopterygii
Order – Gymontiformes
Family – Gymnotidae
Genus – Electrophorus
Species – electricus
Related Species – Despite appearances Electric Eels are not related to true eels and are instead a member of the Knife Fish family. (1)
A Shocking Development
Electric Eels are the largest members of the Knife Fish family, reaching a length of 2m and a weight of 20kg, although slightly larger specimens have been recorded. Unlike the majority of fish, the Electric Eel is an obligate air breather, and has to surface every ten minutes to take a gulp of atmospheric air (2). Electric eels are almost blind, not being able to distinguish anything more than the difference between light and shadow, and instead navigate via echolocation and electroreception. To aid in navigation all the eel’s vital organs are located in the front 20% of the fishes body, with the remaining 80% lined with three electric organs; the Main Organ, the Sach’s Organ and the Hunter’s Organ.
When used solely for the navigation, electrical discharges are emitted by the Sach’s Organ and are kept at a low level (around 10V and 25Hertz). When a potential prey item disturbs the electrical field around the Electric Eel, the fish opens ionic channels from the Sach’s Organ to the main and Hunter’s organs, stimulating the electricity producing cells and creating a short yet powerful electrical discharge of over 800V and 1 ampre of current, stunning or even outright killing their prey. In addition to attack the electrical discharges are used in defence, with an adult electric eel able to cycle intermittent electrical shocks every few seconds for up to an hour (3).
During the breeding season male electric eels build nests of saliva, before attracting the female to his territory by modulating the electrical discharges from the Sach’s Organ. After laying the eggs in the nest the female eel leaves, and the male aggressively defends both the eggs and newly hatched fry from predation until their electrical organs develop enough to create their own electrical discharges.
Ecology 101: An Introduction to Environmental Mechanics #13 – Electroreception in Nature
In 1750, history states that the well renowned scientist Benjamin Franklin gathered the electrical energy of a thunderstorm using a kite with a key attached, becoming the first person to harness atmospheric electrical energy. However long before 1750, the natural world had harnessed the power of electricity for communication, navigation and defence. The organisms that can detect and harness electricity are referred to as being electro-receptive and are mostly amphibious or aquatic due to the increased conductive abilities of water.
The most basic electro-receptive ability is electro-location, which is where an animal can detect biological and geological electric fields. A number of fish; such as sharks, sturgeons, lungfish and gars, are able to detect electrical fields, effectively using them to locate hard to find prey and evade obstacles. In addition to fish, both the Platypus (Ornithorhynchus anatinus) and the Western Long-beaked Echidna (Zaglossus bruijini) can also detect electrical fields, with the latter being one of the few terrestrial examples of electroreception, although it has far less electroreceptors than the Platypus.
The actual use of electrical fields is far rarer than their detection, with only a few groups such as the Knife fish, Elephant Nosed Fish, Torpedo Rays and a few others actively creating electrical fields for navigation. The majority of these fields are too weak for predatory usage, often peaking at an output of 1-3V, and are labelled as ‘weakly electric fish’. Despite their limited output these fields are useful for navigation and communication, with most of these ‘weakly electrical fish’ living in murky water or are nocturnal. In some instances such electrical fields can be used to deceive predators, with the Bluntnose Knifefish (Brachyhypopomus sp) mimicking the passive discharge pattern of the electric eel to dissuade larger fish from attacking it.
Only three groups of fish (Knifefish, Torpedo Rays, Electrical Catfish) create active electrical discharges for predatory reasons. While the electric eel is the most well-known of these ‘strongly electric fish’, it is the Torpedo Rays that produce the deadliest discharges, partially due to the greater conductivity of salt water in comparison to fresh water. While the voltage from the ray is much lower, peaking at 200V, the discharge reaches a current of 30amperes, allowing it to stun larger prey and predator species.
While Benjamin Franklin may have been the first person to harness atmospheric electricity, it was the ancient Egyptians who were the first people (on record) to use electricity. The Electric Catfish (Malapterurus electricus) was well known to the Egyptians, with carvings of the fish on the walls of tombs dating back 5000 years. Fishermen on the Nile had a healthy respect for the fish referred to in ancient texts as ‘the Thunderers of the Nile.
2 - Johansen, Kjell (1968). "Gas Exchange and Control of Breathing in the Electric Eel, Electrophorus electricus". Z. Vergl. Physiologie (Springer Berlin / Heidelberg) (Volume 61, Number 2 / June, 1968): 137–163.
3 – Catania, Kenneth C. (2015-10-29). "Electric Eels Concentrate Their Electric Field to Induce Involuntary Fatigue in Struggling Prey". Current Biology25: 1–10
4 – Stoddard, P. K. (1999). "Predation enhances complexity in the evolution of electric fish signals".Nature400(6741): 254–256
1 - http://cdn1.arkive.org/media/52/5265073B-F144-463E-ABD8-EE9D0EED8CF4/Presentation.Large/Electric-eel-in-habitat.jpg
2 - http://images.nationalgeographic.com/wpf/media-live/graphic/map-electric-eel-160-20040-cb1273160910.gif
3 - http://www.aqua.org/~/media/Images/Animals/Electric%20Eel/animals-electriceel-slide1-web.jpg
4 - http://animal.memozee.com/ArchOLD-4/1126845155.jpg
5 - https://upload.wikimedia.org/wikipedia/commons/b/b5/Malapterurus_electricus_1.jpg
Talk about an electrifying issue, all this discharge is bound to cause an overload somewhere down the line. As for clues on next week’s animal; well it can fly, is nocturnal, uses echolocation and eats fruit…sounds simple right. Well we’ll see next week, but until then critic, comment and suggest future issues as well as making sure you check past issues in Impurest’s Bestiary.