Black Ghost knifefish

(Apteronotus albifrons) 

The Black Ghost Knifefish is known from rapidly flowing creeks with sandy substrates. This nocturnal oddball is a micro-predator of insect larvae and small fish, and possesses a weakly discharging neurogenic electric organ and ampullary electro receptors that are distributed from head to tail. This means that the fish can not only sense electrical impulses, but can send them as well. These electrosensory systems are used mainly for electro-location, navigation, and communication, and are relatively weak as electric fish go, so pose no risk to the aquarist. This is a endearing fish which is an all over inky black colour except for a white patch on the dorsal surface of the nose/head and two white rings on the slender tail. It moves in a graceful manner by undulating the long anal fin - which stretches the length of the belly, from just under the base of the pectoral fins to the caudal peduncle - and is capable of swimming forwards or backwards with ease. The Black Ghost Knifefish is reasonably easy to keep, provided that some key requirements are met. Firstly, this fish grows very large and cannot really bend, so a voluminous aquarium (at least 6ft long and a minimum 2.5ft wide) is a must. Secondly, the knifefish must be provided with a choice of shady hiding spots e.g. wide PVC tubes, rocky caves/overhangs (do ensure such structures are stable), and large tangles of driftwood. The lighting should not be too bright as these nocturnal fish are sensitive to intense illumination; if the tank must be brightly lit in some areas, provide plenty of broad leaved aquatic plants and floating species to help diffuse the light. Nonetheless, there absolutely must be areas of darkness within the tank that the fish can retreat to during the day as necessary. The substrate should consist of soft sand in order that the fish may grub about safely when searching for food, and so that the delicate anal fin does not become torn in any sharp gravel. Decent filtration, and moderate levels of flow and oxygenation are required, along with a consistent maintenance regime encompassing regular partial water changes, as these fish are sensitive to elevated nitrate and sudden changes in water chemistry. Black Ghost Knifefish are generally peaceful with other fish (which are large enough not to be eaten overnight), but they are territorial with their own kind and other knifefish, so should be kept one to a tank and not with any other knifefish species. There is also the added problem that in the confines of the home aquarium, electrogenic fish can sometimes become stressed by the presence of other such species due to their electrical fields overlapping. Tankmates should be of similar temperament and large enough not to be considered a snack; good companions could include angelfish, eartheaters (Geophagus spp.), medium sized gouramis, large rainbowfish etc. Avoid housing with any aggressive or boisterous species, and do not attempt to keep alongside snails or shrimps as these would be predated upon. When first introduced to the aquarium, the Black Ghost Knifefish is often very shy, but over time, it will gain confidence - indeed, some specimens may become so tame that they may take food from the hand of the aquarist, or even sit in the hand itself whilst feeding. Blue moon lighting, timed to come on just before the main lights switch off in the evening, is useful in observing your knifefish for a few hours under its preferred subdued lighting. Hopefully, if the tank is maintained appropriately and new fish are quarantined carefully before adding the main aquarium, the need for medications should not arise. However, if treatment is required, take much care as these fish are classed as 'scaleless' and are particularly sensitive to medications (always check with the manufacturer before using - some treatments are not safe, and others may need half dosing). Many aquarists also find that running a UV steriliser on the tank helps to eliminate pathogens and safeguards against the need for putting treatment in the water. The scientific name Apteronotus is from the Greek 'apteros' (without wings) and 'noton' (back) in allusion to the lack of dorsal fin. This is a long-lived and fascinating species to look after, but this fish is quite a commitment so do ensure  that all of its specific care requirements can be met before purchase.

https://www.fishkeeper.co.uk/fish/freshwater/miscellaneous/black-ghost-knifefish