Can Arapaima and Electric Blue Johannii Live Together?
Arapaima and Electric Blue Johannii are not recommended as tank mates due to conflicting pH requirements. Housing these species together is likely to result in stress, health problems, or direct harm to one or both fish.
At a Glance
Can your tank handle Arapaima and Electric Blue Johannii?
Compatibility is only part of the answer. Test both fish with your real tank size, current stock, and maintenance needs to see if you have enough space and a safe stocking level before you add them.
Behaviour & Temperament
Arapaima is a semi-aggressive species (7/10), while Electric Blue Johannii is semi-aggressive (8/10). This modest difference means Electric Blue Johannii may occasionally assert dominance over Arapaima.
Both Arapaima and Electric Blue Johannii are highly aggressive, increasing the risk of violent confrontations.
Arapaima and Electric Blue Johannii both frequent the Middle (Open Water) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.
Worth noting: Arapaima is a known jumper, so a tight-fitting lid is essential.
Water Parameters
The safe temperature window for both species falls between 24°C and 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.
The pH requirements of Arapaima (6–7.5) and Electric Blue Johannii (7.8–8.6) do not overlap, making it impossible to satisfy both species simultaneously.
For general hardness, the shared comfort zone is 10–15 dGH. Regular testing will ensure conditions stay within this range.
Tank Setup
To house Arapaima and Electric Blue Johannii together, plan for an aquarium of at least 15000 litres with a minimum length of 600 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.
Providing a mix of open swimming space and sheltered areas with rocks, driftwood, or plants will keep both species comfortable and allow natural behaviour.
Specific environmental needs for this combination include: Sand (Sifters), Established Algae (Otocinclus). Meeting these requirements will help both species thrive.
Both species do well with low (still water) water movement, so a standard filtration setup rated for the tank volume should suffice.
Why This Pairing Usually Fails in Practice
Arapaima and Electric Blue Johannii are the kind of pair that can look acceptable in a shop but become a maintenance problem at home. The main risk is not a single number in the chart; it is the way incompatible behavior, water needs, or pressure on space compounds over time once both fish are established in the same tank.
Frequently Asked Questions
Can Arapaima and Electric Blue Johannii live together?
No. This combination is not recommended. Key incompatibilities — such as critical behavioural conflicts — make cohabitation unsafe.
What size tank do Arapaima and Electric Blue Johannii need?
A minimum of 15000 litres (tank length at least 600 cm) is recommended. This provides enough space for both species to establish their own areas and reduces the likelihood of territorial disputes.
What water temperature is best for Arapaima and Electric Blue Johannii together?
Keep the aquarium between 24°C and 28°C. A target of around 26.0°C sits comfortably within both species' preferred ranges.
Are Arapaima or Electric Blue Johannii aggressive?
Arapaima is semi-aggressive (7/10) and Electric Blue Johannii is semi-aggressive (8/10). Their similar temperaments generally lead to a peaceful coexistence.
What pH do Arapaima and Electric Blue Johannii need?
Their pH requirements do not overlap. Arapaima prefers 6–7.5, while Electric Blue Johannii needs 7.8–8.6. This makes them incompatible in the same water chemistry.
How do I manage Electric Blue Johannii's territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Electric Blue Johannii space to claim a territory without encroaching on the other fish's area. Adding décor that divides the tank into distinct zones works especially well.
Shared setup supplies
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Guidarium Editorial Desk
Reviewed against Guidarium care, stocking, and compatibility standards. Read the editorial policy.
- Last reviewed
- May 4, 2026
- Last updated
- May 4, 2026
- Issues or corrections?
- Contact the editorial team
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