The black ghost knifefish (Apteronotus albifrons) is a tropical ornamental fish belonging to the ghost knifefish family (Apteronotidae). They originate in freshwater habitats in South America where they range from Venezuela to the Paraguay–Paraná River, including the Amazon Basin. They are popular in aquaria. 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 length of .
Black ghost knifefish are nocturnal. They are a weakly electric fish which use an electric organ and receptors distributed over the length of their body in order to locate prey, including insect larvae. Pale bands on the tail are a synapomorphy for its monophyletic clade. The presence of these two semi-clear bands encircle the caudal end of the fish throughout its development, clearly signifying the A. albifrons species complex. The
black ghost knifefish is benthopelagic, so they live in the water column and the bottom of bodies of water.
thumb|Black ghost knifefish from another underside view to show the undulating movement of the large extended dorsal/caudal fin
Systematics
thumb|Phylogenetic tree displaying the interrelatonships among the Apteronotidae genera. Apteronotus albifrons is included in this tree.
The first recorded species of the Gymnotidae family is the Gymnotus carapo in Brazil discovered by Georg Maregraf in 1648. The black ghost knifefish was then first recorded in 1766 by Carl Linnaeus.
Electricity
The black ghost knifefish is a weakly electric fish as a result of the electromotor and electrosensory systems it possesses. Electrogenesis occurs when a specialized electric organ found in the tail of the fish generates electrical signals, which are thus called electric organ discharges (EODs). Then, for these EODs to be sensed by the fish, electroreception occurs when groups of sensory cells embedded in the skin, known as electroreceptor organs, detect the electrical change. The EODs are used for two major purposes: electrolocation and communication.
The kind of EOD produced can be used to distinguish between two types of weakly electric fish: the pulse-type and the wave-type. The black ghost knifefish are considered to be the latter type, because they can continuously generate EODs in small intervals. Wave-type EODs have a narrow power spectra, and can be heard as a tonal sound, where the discharge rate establishes the fundamental frequency. As nocturnal hunters, the fish can rely on all three systems to navigate through dark environments and detect their prey. The baseline frequency is maintained to be almost constant at stable temperature, but will usually be changed due to the presence of others of the same species. Such changes in frequency relevant to social interaction are called frequency modulations (FMs). The role these FMs have in communication is significant, as black ghost knifefish have developed jamming avoidance responses, which are behavioral responses that avoid the overlapping of EOD frequencies between conspecific individuals to prevent sensory confusion. This ribbon-fin locomotion likely evolved to allow specialization in fish for higher maneuverability. This unusual locomotive system gives the fish the ability to swim in all directions (forwards, backwards, and sideways) and also hover. They can even swim upside down.
Life history
In regards to reproduction, members of the gymnotiform order are fractional spawners, so the black ghost knifefish spawn their sticky eggs irregularly, as the number of eggs spawned is not consistent every time. Their fecundity can range from 1 to 105 eggs. They also choose spawning sites carefully to ensure well-hidden eggs. The Apteronotus species will hide eggs one at a time in tiny holes or gaps in the environment. Eggs are also deposited at night to early morning between 11 pm and 2 am using their electrosensory object location abilities. This fish is useful in inspiring new designs for underwater vehicles due to their high maneuverability while maintaining a straight and rigid body.
Conservation status and efforts
The black ghost knifefish has been listed as Least Concern on the IUCN Red list since 2020.