General info
Fish that can generate electric fields are called electric fish or electrogenic. Fish that can detect electric fields are called electroreceptive. All electrogenic fish are electroreceptive. Some fish such as sharks, rays and catfish can detect electric fields, but cannot generate electric fields. There three types of electric fish: fish that can detect electric currents, strongly electric fish, and weakly electric. Fish that can detect electric currents include sharks, rays and paddlefish. These fish locate their prey by detecting the electric currents produced by the prey animal. All living cells, tissues and organisms produce electromagnetic fields. Sharks and rays use electroreceptor organs called the Ampullae de Lorenzini to detect electric the electric currents produced by all living things allowing them to find prey that is hidden in the sand. Strongly electric fish can discharge strong electric shock to stun their prey and for defense. Strongly electric fish include the electric eel and electric rays. These fish can produce an electric discharge ranging from 10 to 500 volts with up to a 1 Amp current producing 500 watts of power. This is a strong enough current to be fatal to humans.
Weakly electric fish produce weak electric fields used for sensing their environment and possibly for communicating with other weakly electric fish. Weakly electric fish produce an electric discharge of less than a volt. There are two types of the weakly electric fish, the Gymnotiforms that originated in South America and the African Mormyriforms. Weakly electric fish emit either "hums" or "clicks" as a way of mapping their environment. "Hummers" have a wave-type electric discharge organ (EOD) and emit a wave-like hum, whereas "clickers" have a pulse-type EOD and emit short pulses
Black Ghost Knifefish
The black ghost knifefish, Apteronotus albifrons, is a tropical fish belonging to the ghost knifefish family. The black ghost knifefish lives in fast moving, sandy bottom creeks in a tropical climate. They are native to South America in the Amazon Basin. They are popular in the aquarium trade and are tank raised in Asia. The fish is all black except for two white rings on its tail, and a white blaze on its nose, which can occasionally extend into a stripe down its back. It moves mainly by undulating a long fin on its underside. It will grow to a maximum length of 20 inches. They are nocturnal, but they are weakly electric fish and use an electric organ and receptors distributed over the length of their body in order to locate insect larvae. Black Ghosts can become aggressive with same sex members of their own species and members of other, similar species. Other than that, they are usually quite timid.
Black Ghost Knifefish Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gumnotiformes
Family: Apteronotidae
Genus: Apteronotus
Species: albifrons
Care and Maintenance
Black Ghost Knifefish are carnivores. In the wild they are nocturnal, when the sun sets and throughout the night they feed on insect larvae. The aquarium for the Black ghost should be larger than 50 gallons with a small-grained substrate. It should be fairly densely planted with many floating plants. The floating plants will help the fish overcome its shyness, as it is nocturnal and sensitive to bright lights. Driftwood is also recommended along with some sort of inert piping for the fish to hide in. They require good hiding places and will not do well with aggressive tank mates. The water should be soft, and kept at a temperature between seventy-five and eighty-two degrees. The pH should be neutral to acid. Feeding should be a mix of live tubifex brine shrimp and meaty frozen foods. The Black ghost is sensitive to water pollutants, changes in water conditions, and medications. They are sensitive to some fish medications such as copper and those containing formalin.
Description
The black body of the Black Ghost Knifefish is flat and elongated. It has a continuous fin along the underside formed by a joining of the caudal and anal fin and moves with an undulating motion. Although they appear clumsy, they have a built in radar system that uses low voltage electricity to help them navigate. This and their undulating lower fin allow them to gracefully move forwards and backwards through the aquarium.
Weakly Electric Fields
Weakly electric fish generate a discharge that is typically less than one volt in amplitude. Electric fields of on volt or less are too weak to stun prey, but are used for navigation, object detection (electrolocation) and communication with other electric fish (electrocommunication).
Electroreception
In passive electroreception the animal senses the weak bioelectric fields generated by other animals. In active electroreception, the animal senses its surrounding environment by generating electric fields and detecting distortions in these fields using electroreceptor organs. Active electrolocation is especially important in murky water, where visibility is low. Animals that use active electroreception include the weakly electric fish, which generate small electrical pulses using an organ in the tail consisting of two to five rows of modified muscle cells. Weakly electric fish characterize the environment in which they live by sensing distortions in their self-generated electric field. These distortions result in electric images forming across their skin. Weakly electric fish can discriminate between objects with different resistance values, which may help in identifying the object. They can also communicate by modulating the electrical waveform they generate, an ability known as electrocommunication. Active electroreception typically has a range of about one body length, though objects with an electrical resistance similar to that of the surrounding water are nearly undetectable.
Electric Organ
Electrocytes, electroplaques or electroplaxes are cells used by rays, electric eels and other electric fish for electroreception. They are flat disk-like cells that are positively charged on one side and negatively charged on the other. The cells function by pumping positive sodium and potassium ions out of the cell with transport proteins powered by ATP. The electric organ is made up of modified muscle or nerve cells, which became specialized for producing electric fields. For most electric fish, the electric organ is located in the tail. The output of the organ is called the electric organ discharge and is abbreviated EOD. Electric organ discharge (EOD) is the electric current generated by the organs of animals including electric fish. In some cases the electric discharge is strong and is used for protection from predators; in other cases it is weak and it is used for navigation and communication. A fish using electrolocation determines an objects shape and location relative to its own body simply by the shape and location of the electric image the object makes. Where the electric image falls depends on where the impeding object lies, so analysis of the electric image location on the body will tell where the object is in relation to the body. Similarly, the shape of the electric image reflects the shape of the object.
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical axis, plotted as a function of time. Although an oscilloscope displays voltage on its vertical axis, any other quantity that can be converted to a voltage can be displayed as well. In most instances, oscilloscopes show events that repeat with either no change, or change slowly.
Oscilloscopes are commonly used to observe the exact wave shape of an electrical signal. In addition to the amplitude of the signal, an oscilloscope can show distortion, the time between two events and relative timing of two related signals. The digital storage oscilloscope, or DSO for short, is now the preferred type for most industrial applications. It replaces the unreliable storage method used in analog storage scopes with digital memory, which can store data as long as required without degradation. It also allows complex processing of the signal by high-speed digital signal processing circuits.
Respirometry
Respirometry is a number of techniques used to determining the metabolic rate of an organism. The metabolism of an animal can be determined by recording the rate of carbon dioxide production and the rate of oxygen production. The following two measures of metabolic rate are usually determined: the resting or basal metabolic rate and the highest or maximal rate. The rate of carbon dioxide production is designated by VCO2 and the rate of oxygen consumption by VO2. VO2max is the maximum oxygen consumption by the test organism and is recorded while the organism is undergoing intense aerobic exercise. Another metabolic measure, called field metabolic rate or FMR, is determined when the animal is active in the natural environment. Metabolic rates can be reported as whole-animal values meaning the rate is not adjusted for body mass. A more meaningful way to compare metabolic rates between different animals is to calculate the rate per gram or kilogram of body mass.
Closed Respirometry
In a closed respirometry system, the organism is sealed in a sealed chamber and the oxygen consumption is recorded over time. If the chamber is not opened the animal will eventually become hypoxic and then die.
Open Respirometry
In an open respirometry system, air or water is allowed to flow through the system so that the test animal does not use up all the available oxygen. The flow rate must be carefully matched to the test animal size so that the oxygen level does not drop too low while still allowing the consumption of enough oxygen to be measured.
Respirometer
A respirometer is a device used to measure the rate of respiration of a living organism by measuring its rate of exchange of oxygen and carbon dioxide. Respirometers are designed to measure respiration either on the level of a whole animal or on the cellular level. Respirometer systems vary greatly in design depending on the goals of the study and the technology available. Basic components of a respirometer include: pump, flow meter, tubing, chambers, scrubbing tubes to remove water and CO2, gas analyzers and possible a computer control and data recording system. The two most common gas analyzers are a carbon dioxide analyzer and an oxygen analyzer.
