There are four groups of teleost fish belonging to two distantly related taxa (the Ostariophysi and the Osteoglossiformes) that posses electroreceptor organs (Beckmann 2004: 975). These receptor organs detect weak bioelectric fields that emanate from living prey items. In addition, some fish have tuberous receptor organs that generate weak electric fields. In a process called active electrolocation, fish use a measure of their electric organ discharges (EODs)--which are essentially outputs of wave frequencies--to detect the presence of a nearby object. They do so by transmitting small electrical pulses (i.e., frequencies) through their organs; when these pulses hit an object near-by they are reverberated back to the fish. The fish then uses the change in the amplitude of these frequencies to recognize the presence of that object; some weakly electric fish are even able to identify some material properties of the object itself. The process is described thoroughly in Dr. Beckmann's paper. Studying the intricacies of such processes can lead to the development of sensors that cause minimal disturbance to the marine life that pass through their electric fields.
Future underwater vehicles will be increasingly called upon to work in cluttered environments and to interact with their surroundings. These vehicles will need sensors that work efficiently at short range and be highly maneuverable at low speed. To obtain insights into principles and mechanisms of low-speed operation in cluttered environments, we examine a fish that excels in this regime, the black ghost knifefish Apteronotus albifrons. This fish hunts in dark or turbid water using a short-range self-generated electric field to sense its surroundings. Coupled with this unique mode of sensing is an unusual ribbon fin propulsion system that confers high multidirectional maneuverability at low speeds. To better understand the relationship between body morphology and common maneuvers of this fish, we utilized an idealized ellipsoidal body model, Kirchhoff's equations, and an optimal control algorithm for generating trajectories. We present evidence that common fish trajectories are optimal, and that these trajectories complement the sensory abilities of the fish. We also discuss prototypes of the sensing and propulsion systems of the fish with a view to providing alternative approaches for underwater vehicle design where high maneuverability in geometrically complex environments is needed.
Evolution of Time-Coding Systems in Weakly Electric Fishes
Weakly electric fishes emit electric organ discharges (EODs) from their tail electric organs and sense feedback signals from their EODs by electroreceptors in the skin. The electric sense is utilized for various behaviors, including electrolocation, electrocommunication, and the Jamming avoidance response (JAR). For each behavior, various types of sensory Information are embedded in the transient electrical signals produced by the fish. These temporal signals are sampled, encoded, and further processed by peripheral and central neurons specialized for time coding. There are time codes for the sex or species Identities of other fish or the resistance and capacitance of objects. In the central nervous system, specialized neural elements exist for decoding time codes for different behavioral functions. Comparative studies allow phylogenetic comparison of time-coding neural systems among weakly electric fishes.
A Shocking Group of Fish and Eels
by Frank Sherwin, M.A. *
Imagine going to a doctor with a flare-up of gout or a migraine. To your utter shock, the physician calmly instructs you to reach into a water tank and hug an electric fish. This is what Roman physician Scribonius Largus prescribed in his Compositiones Medicae in 46 AD, and it worked too well, probably killing the patient.
Some of the more amazing fish are those that are designed to produce electricity. The South American electric eel of the genus Electrophorus can produce almost 600 volts, enough to stun a man and even knock a horse off its feet. Like the pacemaker in a heart patient's heart, these creatures use bioelectric generators to build up, then rapidly discharge a shock. The neurotransmitter acetylcholine is released from electromotor neurons (nerve cells) to the eel's neatly-stacked electrocytes (the voltage-generating cells) and zap!
The Pacific electric ray (Torpedo) can also deliver a jolt when bothered. And a family of fish called stargazers, with heavy, large heads, are designed to remain motionless on the bottom until a victim swims nearby. Then the prey is stunned with a 50-volt punch and eaten.
Researchers long ago learned that these aquatic creatures had bundles of muscle fibers that act much like a car battery. These fibers are highly efficient, able to deliver discharges hundreds of times per second at different voltages according to the creature's need. How do electric fish and eels generate their charges, as well as use them for a wide variety of purposes? Is there a cogent and compelling evolutionary explanation?
In 2004, British and French scientists discovered that weakly electric fish in Africa and South America send out pulses and waves of electricity, respectively. This is fascinating because they hunt tiny larvae at night, when their eyes are useless. So the Creator gave them electric eyes. Neuroscientist Curtis Bell of Oregon Health & Science University described how the fish can “see their three-dimensional electrical world.”1
Christian Graff of the Laboratoire de Biologie du Comportement in Grenoble, France, and three others used the term "electroperception" to describe how the fish can discern distances, shapes, motions, and textures.2 Each object the fish encounters has its own electrical signature. The fish detects that signature with special nerve structures in its skin that act like a retina, although these sensors are tuned to electricity rather than light. The rich amount of information received is coordinated and mapped to produce a 3D color image.
Electric eels have stimulated the field of medical implants. Researchers at Yale University and the National Institute of Standards and Technology seem to recognize superior design, if not the obvious implication of the superior Designer:
Applying modern engineering design tools to one of the basic units of life, they argue that artificial cells could be built that not only replicate the electrical behavior of electric eel cells but in fact improve on them.3
NIST engineer David LaVan also used this creation language while addressing model electric eel cells.
Do we understand how a cell produces electricity well enough to design one--and to optimize that design?4
If humans, as intelligent agents, have a difficult time reverse-engineering biological mechanisms like these electricity-producing organs, then it is reasonable to assume that nature, as an unintelligent non-agent, was not responsible for the initial engineering. As shocking as this idea is to worshippers of nature, that glory belongs to the Creator.