Can Blackline Rasbora and Figure 8 Puffer (Brackish) Live Together?
Blackline Rasbora and Figure 8 Puffer (Brackish) are not recommended as tank mates due to incompatible water types. 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 Blackline Rasbora and Figure 8 Puffer (Brackish)?
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.
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Behaviour & Temperament
Blackline Rasbora is a peaceful species (1/10), while Figure 8 Puffer (Brackish) is semi-aggressive (8/10). This notable difference means Figure 8 Puffer (Brackish) may occasionally assert dominance over Blackline Rasbora.
Large aggression gap (7 points) between Blackline Rasbora and Figure 8 Puffer (Brackish) increases stress risk for the more peaceful fish.
Blackline Rasbora and Figure 8 Puffer (Brackish) 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: Blackline Rasbora 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 26°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.
Both fish can tolerate a pH between 7.5 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.
For general hardness, the shared comfort zone is 10–15 dGH. Regular testing will ensure conditions stay within this range.
Crucially, these species require different water types — one needs freshwater while the other requires brackish conditions. This is a hard barrier to keeping them together.
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Tank Setup
To house Blackline Rasbora and Figure 8 Puffer (Brackish) together, plan for an aquarium of at least 60 litres with a minimum length of 60 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: Plants - Densely covered, Driftwood (Digestion/Hiding), Leaf Litter/Blackwater, Sand (Sifters), Shells (Breeding/Hiding). Meeting these requirements will help both species thrive.
Both species do well with moderate (standard) water movement, so a standard filtration setup rated for the tank volume should suffice.
Suitable Tank Sizes
Standard aquarium sizes large enough for both Blackline Rasbora and Figure 8 Puffer (Brackish).
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
40 Gallon Breeder
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Frequently Asked Questions
Can Blackline Rasbora and Figure 8 Puffer (Brackish) live together?
No. This combination is not recommended. Key incompatibilities — such as different water type needs — make cohabitation unsafe.
What size tank do Blackline Rasbora and Figure 8 Puffer (Brackish) need?
A minimum of 60 litres (tank length at least 60 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 Blackline Rasbora and Figure 8 Puffer (Brackish) together?
Keep the aquarium between 24°C and 26°C. A target of around 25.0°C sits comfortably within both species' preferred ranges.
Are Blackline Rasbora or Figure 8 Puffer (Brackish) aggressive?
Blackline Rasbora is peaceful (1/10) and Figure 8 Puffer (Brackish) is semi-aggressive (8/10). The gap in aggression levels means the calmer fish may experience stress from the more assertive one.
What pH do Blackline Rasbora and Figure 8 Puffer (Brackish) need?
Both species overlap in the 7.5–7.5 pH range. Consistency is key — avoid sudden swings, and test regularly to stay within this window.
Will Figure 8 Puffer (Brackish) nip Blackline Rasbora's fins?
Figure 8 Puffer (Brackish) is a known fin nipper. If Blackline Rasbora has long or flowing fins, there is a real risk of fin damage. Keeping Figure 8 Puffer (Brackish) in a larger group can help redirect nipping behaviour toward conspecifics.
How do I manage Figure 8 Puffer (Brackish)'s territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Figure 8 Puffer (Brackish) 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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