Compatibility Report
GuideMyTank compatibility analysis for American Flagfish and Black Ghost Knifefish.
Planning verdict
incompatibleDo not plan a shared aquarium for this pair. Choose a different tank mate or maintain separate aquariums.
American Flagfish and Black Ghost Knifefish receive a not recommended verdict from the current structured assessment. American Flagfish is recorded as semi-aggressive with an aggression level of 4/10; Black Ghost Knifefish is recorded as semi-aggressive with an aggression level of 4/10. The recommendation is based on the combined water, space, behavior, grouping, and predation checks below rather than on species names alone.
American Flagfish has a recorded temperature range of 64–78°F and pH range of 6.5–8. Black Ghost Knifefish is recorded at 73–82°F and pH 6–7.5. Their shared planning window is 73–78°F for temperature and 6.5–7.5 for pH. A shared aquarium must stay inside the overlap rather than merely touching each species’ outer tolerance.
Black Ghost Knifefish sets the larger listed base aquarium requirement at 90 gallons; the other listed minimum is 20 gallons. Black Ghost Knifefish is the larger adult by the recorded maximum, reaching 20 inches, compared with 2.5 inches. These figures are starting constraints, not a stocking-capacity calculation, because the complete group sizes and bioload still matter.
American Flagfish is a moderate species associated with the mid zone and low flow. Black Ghost Knifefish is moderate, uses the cave zone, and has a moderate flow preference. American Flagfish should be planned as a group of at least 2, while black ghost knifefish does not have a recorded minimum school larger than one. The aquarium must support both social structures without forcing either species into insufficient space.
American Flagfish is recorded as a omnivore with intermediate care, while Black Ghost Knifefish is a carnivore with advanced care. Their listed preferred tank styles are community and blackwater. Feeding access, cover, open swimming room, filtration, and observation should be planned around the more demanding requirement rather than averaged between the two species.
Use these pair-specific boundaries before treating the verdict as an acceptable stocking plan.
Do not plan a shared aquarium for this pair. Choose a different tank mate or maintain separate aquariums.
These references support the underlying species records used by this assessment. They do not necessarily evaluate this exact pair together.
Continue with the most relevant care and compatibility resources for American Flagfish and Black Ghost Knifefish.