Weakly Electric Fish in Aquaristics: A Portrait of the White-cheeked Knifefish (Apteronotus albifrons)

They are interesting fish that are suitable only for certain aquariums because they require specific conditions. Even if you meet those, you have little chance of breeding the white-bellied knifefish. Literary experiences with this fish are scarce, ranking it among aquarium rarities. Ideally, it is captured by the English name "black ghost," meaning black spirit, apparition, phantom, shade, demon, …

Occurrence of fish

The fish live in a vast area of South America, which is bordered to the north by the Orinoco and to the south by the Rio Paraná. In other words, it is found in Brazil, Guyana, Venezuela, Peru, and Ecuador.

Characteristics

The white-bellied knifefish reached Europe in 1934 under the old name Sternarchus albifrons. They have never become popular aquarium fish, although they have all the prerequisites for it. The velvety black color is an ideal sales color. The Latin species name albifrons means white forehead. They grow to 40-50 cm, although in most of our conditions they are somewhat smaller. It is said that they can live up to 16 years and grow throughout their lives, thus achieving this impressive length at the end of their life. They are characterized by an electric organ located in the base of the caudal fin, which facilitates not only spatial orientation but also gives them incredible abilities to hunt insect larvae or small fish both at night and in murky water. Generally, it holds true for knifefish that they emit weak electric fields at higher frequencies, which help them determine their position regardless of daylight. In fact, we could compare these electric fields to the sonars of dolphins. Especially young fish utilize this ability and surface at night to catch fallen termites. Their interest in catching insects and their larvae is also used in their hunting. As readers may suspect, black ghosts are fish with nocturnal activity. By evening, their presence in the aquarium manifests itself with significantly increased activity. Suddenly, they are everywhere when during the day they were hidden in shelters. Rarely can we see such elegant fish in aquariums with perfect agility and precision of movements. Very important for them is the large pectoral fin with more than 150 rays, which allows them to swim forward and backward with wavy movements without having to turn, as other fish typically do. You often ask yourself which movement is actually natural for them? Forward or backward? The sexes are very difficult to distinguish; in adulthood, males are somewhat elongated, while females have a shorter and rounded "snout." In the literature describing their diet with other fish, we did not observe them preying on smaller fish but rather consuming them whole.

Breeding in the aquarium

The fish are somewhat intolerant towards each other, aggressive, and due to their size, they also require large aquariums. Fights, however, have a ritual character, proceeding according to certain rules, and do not result in injuries. Opponents stand side by side or opposite each other, delivering head blows to each other. After a certain period, a hierarchy is established in the aquarium, where stronger individuals are respected. The defeated individual retreats in reverse, backing out of the winner's sight, sometimes even slightly on its side, thus paying tribute to the victor. It would be very interesting to study the electric discharges of fish during these conflicts. The electric field serves not only to locate places but also for intraspecies communication. The tanks should be shaded with plenty of hiding places, which can be not only obligatory roots or stones, ceramics, but also common hollow bricks or drainage pipes. Every creature needs its own hiding place. Due to their constant game of hide-and-seek, they are not too popular, as we rarely see them. If we have a school of fish in the aquarium and each fish does not have its own hiding place, then the weakest individuals are out of luck; they must seek alternative solutions, imitating perhaps fallen leaves on the bottom. The bottom should be arranged with finer sand. When changing the water, which we keep warm around 24-27 °C, we ensure that there are no significant changes in chemical parameters, for which the fish could pay with their lives. We primarily keep the fish in schools, as they are then generally calmer and more lively. Tankmates must be of a certain size so they do not serve as quite expensive food.

Feeding

In nature, live food is mainly available, and I still believe that we should not make significant changes. Therefore, we offer live as well as frozen mosquito larvae, daphnia, brine shrimp, small crayfish, and small fish. I must say that they also do not disdain quality artificial food. I tried pellets intended for terrarium fish; the fish, after their fall to the bottom, could not resist, coming out of their hiding places even during the day, similar to what some catfish were also doing in the tank.

Breeding

The general literature on them either stubbornly states they have not been bred or, as the popular "Mergus Atlas," shares that they are unknown. Very interesting attempts by Dr. Frank KIRSCHBAUM (University of Cologne) to breed these fish are known, where he mimicked the rainy season by slowly raising the water level while simultaneously lowering the pH and conductivity. Thanks to him, we learn something about the sexual differences, which are very difficult to determine in these fish. However, when you breed the fish, the differences in sex are obvious. Fully grown males have distinctly longer and sharper mouths, while females have a more blunt mouth. Breeding seems to occur in fish of one year of age, which lay about 2 mm large and yellowish eggs in a cavity that the pair selects beforehand. Hatching occurs at a temperature of 25-27 °C on the third day. At the time of swimming out, the fish are already about 1 cm long, so breeding while feeding with brine shrimp nauplii poses no problems. The fish are initially transparent, whitish, and yellowish, and from about 15 mm they begin to darken.

Images:

1. Male white-bellied knifefish.
2. Female white-bellied knifefish.
3. Sex differences are primarily recognized by the elongated snout; the female has a short and rounded one.
4. Adult male attacks the pair in the shelter, which is now a hollow brick.
5. The aggressor is however firmly repelled.
6. As a good cleaner, Pterygoplichthys gibbiceps serves; its nocturnal activity does not bother the knifefish.
7. School of young knifefish.
8. To breed young knifefish, it is necessary to use larger aquariums.
9. Young knifefish require frequent and abundant feeding.
10. Gnathonemus petersii, the marbled knifefish, grows up to 25 cm and originates from Central Africa, mainly from the Congo and Cameroon regions. It also lives in the upper reaches of the Blue and White Nile. Because these fish usually live in murky waters, they have poor eyesight. They are not completely blind, though; their eyes are covered with a transparent protective membrane. In case of danger, they burrow headfirst into the mud or sand without damaging their eyes. As the only freshwater fish, they can actively rid themselves of ectoparasites by lying on their side (which they can do in a fraction of a second), and then rubbing against the sandy bottom with forward and backward movements. Poor eyesight is compensated by an exceptional ability of other sensory organs, primarily well-functioning lateral lines and taste. They can easily detect impending danger and search for food. The electric organ in the base of the caudal fin emits weak electric impulses, which help the fish find food or sense danger. Similarly to dolphins and bats, they have "sonar," which can be audible to the human ear after amplification.
11. Eigenmania virescens, the green knifefish, also emits weak electric discharges serving for mutual communication. Males grow to 30-35 cm, while females are smaller, only about 20 cm.
12. Petrocephalus sp. belongs to the subfamily Petrocephalinae, which today has about 20 species growing to a size between 10-20 cm. It also belongs to the group of fish that emit weak electric impulses (3-7 V), which help not only with orientation but also with defense. They have large eyes and are active during the day.