Black Ghost Knifefish
Apteronotus albifrons
Description
The Black Ghost Knifefish is a fascinating and unique fish with a long, ribbon-like body that lacks typical fins, instead possessing a specialized, undulating fin along its body that it uses to “swim” in a side-to-side motion. Its dark, nearly black coloration and pale lateral line along its body give it a ghostly appearance, hence its name. The fish has large, bulbous eyes, a long head, and a distinctive electric organ, which it uses to navigate its environment in the wild through electroreception. Black Ghost Knifefish are nocturnal and active, often hiding during the day and becoming more active at night, hunting small prey. They are peaceful but can be territorial, particularly when they feel threatened.
Habitat Origin
Native to South America, particularly the Amazon and Orinoco River basins in Brazil, Colombia, Venezuela, and other surrounding countries. They inhabit slow-moving waters with dense vegetation and are often found in murky, dark waters.
Aquarium
Ideal Number in Aquarium: Typically kept alone, although they may tolerate other peaceful fish in larger tanks.
Favorite Food
Black Ghost Knifefish are carnivores and have a diet consisting of small fish, shrimp, worms, and other live or frozen foods. They will accept high-quality frozen food such as bloodworms, brine shrimp, and small fish. In captivity, it is essential to provide a varied diet to mimic their natural feeding habits. They may also eat pellets and flakes designed for carnivorous fish, but live food is preferred for their hunting behavior.
Behavior:
Black Ghost Knifefish are primarily nocturnal and are best kept in a dimly lit tank, as they thrive in low-light conditions that mimic their natural environment. During the day, they are usually more reclusive and spend time hiding in caves or crevices. At night, they become active, using their electric organ to navigate and locate food. Although they are generally peaceful, they can be territorial, especially if kept in smaller tanks or with aggressive fish. They may display stress or aggression if their space is limited. They are non-aggressive towards smaller fish but should not be kept with species that can easily be eaten or that stress them.
Special Care:
Black Ghost Knifefish require a well-maintained aquarium with plenty of hiding spots, such as caves, driftwood, and plants. A large tank is necessary to provide them with enough space to swim, as they are relatively large fish. They also need stable water conditions, including clean, well-oxygenated water. As electroreceptive fish, they are sensitive to electric fields, so it’s important to avoid equipment that may interfere with their natural navigation, such as magnetic cleaners or powerful filtration systems that create too much turbulence.
Compatibility with Other Fish:
Black Ghost Knifefish are best kept with other peaceful, non-aggressive species. They are compatible with medium-sized fish that won’t be viewed as food. Avoid keeping them with small fish, as the knifefish may try to eat them. They can be kept with other peaceful, medium-sized tankmates, including tetras, catfish, and some species of cichlids. It is important to keep them in larger aquariums to prevent territorial disputes.
Breeding Tank Setup
A separate breeding tank is highly recommended for Black Ghost Knifefish due to their territorial and sometimes aggressive nature, especially during mating. A minimum 40-gallon tank (150 liters) is required for a pair, with a 75-gallon (280 liters) or larger tank preferred for multiple fish. The tank should be long and spacious to accommodate their active swimming. Ideal water conditions include pH 6.0–7.5, temperature 24–28°C (75–82°F), and soft to moderately hard water (4–12 dGH). Use fine gravel or sand, and provide ample hiding spots using driftwood, rocks, and subdued decorations. Install a canister or sump filter for efficient filtration with minimal current, and maintain low to moderate lighting with a 12-hour light/dark cycle to mimic natural rhythms.
Conditioning Adults for Breeding
To prepare Black Ghost Knifefish for breeding, provide a high-protein and varied diet. Feed them frozen or live foods such as brine shrimp, earthworms, bloodworms, daphnia, or even small feeder fish if properly quarantined. While they are primarily carnivores, some finely chopped vegetables like peas or spinach can be added occasionally. Regular 25–30% water changes should be performed weekly. To stimulate spawning, do a larger 50% water change and slightly raise the temperature to 28°C, mimicking conditions of the rainy season in the wild.
Spawning Process
Spawning usually occurs at night or early morning, triggered by stable conditions, warm water, and fresh water changes. The male may guard the eggs, which are small, sticky, and deposited on plants, rocks, or tank decor. A healthy female can lay 100 to 500 eggs in one session. After spawning, it’s important to remove the female to prevent aggression from the guarding male. In some cases, even the male should be removed if there’s risk of egg predation. Eggs usually hatch in 5–7 days, depending on water temperature.
Fry Hatching & Feeding
The fry rely on their yolk sac for the first few days after hatching. Once they begin free-swimming, offer infusoria or liquid fry food, then baby brine shrimp or microworms as they grow. Transition gradually to finely crushed flakes or pellets once they are larger. Keep water clean and stable with daily or alternate-day water changes (10–20%). Maintain temperature at 24–28°C, and avoid overfeeding to prevent ammonia buildup and poor water quality, which can harm the sensitive fry.
Additional Tips & Sexing Adults
Black Ghost Knifefish typically become sexually mature between 1–2 years, with optimal breeding age at 2–3 years. Males are generally slimmer and more active, while females are broader, especially when carrying eggs. Visual sexing is difficult, so breeding pairs are best identified by observing behavior during courtship. To maximize breeding success, avoid stressors such as sudden pH/temperature changes, aggressive tank mates, or overcrowding. Provide a calm, dimly lit, and secure environment to encourage natural behaviors and increase fry survival rates.