Can Black Ocellatus and Clown Killifish Live Together?
Black Ocellatus and Clown Killifish 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 Black Ocellatus and Clown Killifish?
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
Black Ocellatus is a semi-aggressive species (7/10), while Clown Killifish is peaceful (2/10). This notable difference means Black Ocellatus may occasionally assert dominance over Clown Killifish.
In terms of spatial distribution, Black Ocellatus prefers the Bottom (Substrate) zone, whereas Clown Killifish occupies the Top (Surface) zone. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.
Additional behavioural considerations to keep in mind: Shrimp eaters may also prey on very small nano fish.
Worth noting: Clown Killifish is a known jumper, so a tight-fitting lid is essential.
Water Parameters
The safe temperature window for both species falls between 23°C and 27°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.
The pH requirements of Black Ocellatus (7.5–9) and Clown Killifish (5–7) do not overlap, making it impossible to satisfy both species simultaneously.
For general hardness, the shared comfort zone is 8–8 dGH. Regular testing will ensure conditions stay within this range.
Tank Setup
To house Black Ocellatus and Clown Killifish together, plan for an aquarium of at least 40 litres with a minimum length of 45 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), Shells (Breeding/Hiding), Plants - Floating, Plants - Densely covered, Leaf Litter/Blackwater. 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
Black Ocellatus and Clown Killifish 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.
Suitable Tank Sizes
Standard aquarium sizes large enough for both Black Ocellatus and Clown Killifish.
15 Gallon Standard
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
Show 21 more tank sizes
Diet & Feeding
Feeding time deserves special attention with this pairing. Black Ocellatus is a known shrimp eater and may prey on small invertebrates or nano fish like Clown Killifish.
Frequently Asked Questions
Can Black Ocellatus and Clown Killifish live together?
No. This combination is not recommended. Key incompatibilities — such as critical behavioural conflicts — make cohabitation unsafe.
What size tank do Black Ocellatus and Clown Killifish need?
A minimum of 40 litres (tank length at least 45 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 Black Ocellatus and Clown Killifish together?
Keep the aquarium between 23°C and 27°C. A target of around 25.0°C sits comfortably within both species' preferred ranges.
Are Black Ocellatus or Clown Killifish aggressive?
Black Ocellatus is semi-aggressive (7/10) and Clown Killifish is peaceful (2/10). The gap in aggression levels means the calmer fish may experience stress from the more assertive one.
What pH do Black Ocellatus and Clown Killifish need?
Their pH requirements do not overlap. Black Ocellatus prefers 7.5–9, while Clown Killifish needs 5–7. This makes them incompatible in the same water chemistry.
How do I manage Black Ocellatus's territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Black Ocellatus 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.
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Guidarium Editorial Desk
Reviewed against Guidarium care, stocking, and compatibility standards. Read the editorial policy.
- Last reviewed
- May 1, 2026
- Last updated
- May 1, 2026
- Issues or corrections?
- Contact the editorial team
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