Black Ghost Knife 4.5”

Black Ghost Knife – 4.5" (Apteronotus albifrons)

Appearance & Behavior

With a velvety black body, pale head marking, and white bands near the tail, the Black Ghost Knife makes a striking centerpiece for a spacious freshwater aquarium. Its long underside fin ripples like a ribbon, allowing it to glide forward and backward with remarkable control. Most active at dusk and after dark, this shy predator uses a weak electric field to help navigate and locate food. Give it a sheltered retreat, and watch it venture out as the lights dim.

Quick Care Guide

• Care level: advanced; requires a large, mature aquarium and attentive feeding.
• Temperament: generally peaceful toward suitably sized tankmates, but predatory toward small animals and territorial with other knifefish.
• Size listed: approximately 4.5 inches at sale, not adult size.
• Adult size: can reach approximately 18–20 inches.
• Aquarium: plan for 150 gallons or larger with a long, wide footprint suitable for an adult. A juvenile's small size does not reduce its long-term space needs.
• Temperature: 75–82°F.
• pH: approximately 6.0–7.5; stable conditions are more important than chasing a specific value.
• Water hardness: soft to moderately hard freshwater.
• Diet: carnivore; offer varied, appropriately sized meaty foods.
• Swimming area: primarily lower levels and sheltered areas, especially during daylight.

Aquarium Setup & Compatibility

Provide a fully cycled aquarium with strong biological filtration, good oxygenation, and regular water changes. Use sand or smooth gravel, rounded decor, and roomy caves or tubes that accommodate the fish as it grows. Dim lighting and shaded areas help it feel secure. Maintain open swimming space, protect filter intakes, and fit a secure lid. Avoid sharp decorations that could injure its delicate body.

Choose calm tankmates too large to be swallowed, and avoid aggressive cichlids, fin nippers, and boisterous fish that may harass it or monopolize food. Small fish and shrimp can become prey, particularly as the knife grows. Keeping one Black Ghost Knife per aquarium is the safest approach for most home setups, as other knifefish may provoke territorial conflict.

This species is sensitive to poor water quality and can be sensitive to some medications. Quarantine new arrivals, avoid sudden water-chemistry changes, and confirm any treatment is appropriate for knifefish before use. This is a long-term commitment for an aquarist prepared to provide adult-sized housing.

Feeding

Offer a varied diet of appropriately sized frozen or live foods, such as mysis shrimp, bloodworms, earthworm pieces, and chopped shrimp. Some individuals learn to accept sinking carnivore pellets, but do not assume a new arrival will recognize dry food immediately. Feed near its shelter at dusk or after lights-out, using feeding tongs or a feeding tube if needed to deliver food without crowding the fish.

Confirm that it actually eats rather than relying on leftover community food. Offer modest portions and remove uneaten food promptly. Avoid routine feeder-fish use, which can introduce disease and provide an unbalanced diet.