Can Blackline Rasbora and Masked Julie (Julidochromis) Live Together?
Blackline Rasbora and Masked Julie (Julidochromis) 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 Blackline Rasbora and Masked Julie (Julidochromis)?
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.
Shared setup supplies
We may earn from qualifying purchases
Behaviour & Temperament
Blackline Rasbora is a peaceful species (1/10), while Masked Julie (Julidochromis) is moderately assertive (6/10). This notable difference means Masked Julie (Julidochromis) may occasionally assert dominance over Blackline Rasbora.
Blackline Rasbora and Masked Julie (Julidochromis) 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.
Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion. Aggressive eaters may outcompete shy fish for food, leading to malnutrition.
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 23°C and 26°C. Aim for the midpoint of this range (around 24.5°C) for optimal comfort.
The pH requirements of Blackline Rasbora (6–7.5) and Masked Julie (Julidochromis) (8–9) 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.
Water care products
We may earn from qualifying purchases
Tank Setup
To house Blackline Rasbora and Masked Julie (Julidochromis) 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). 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 Masked Julie (Julidochromis).
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
40 Gallon Breeder
Show 19 more tank sizes
Diet & Feeding
Feeding time deserves special attention with this pairing. Blackline Rasbora is an aggressive eater that may prevent Masked Julie (Julidochromis) from getting enough food.
Because Blackline Rasbora is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Masked Julie (Julidochromis) receives an adequate share.
Feeding products to consider
We may earn from qualifying purchases
.webp?2026-04-25T14%3A35%3A38.022Z)
Frequently Asked Questions
Can Blackline Rasbora and Masked Julie (Julidochromis) live together?
No. This combination is not recommended. Key incompatibilities — such as critical behavioural conflicts — make cohabitation unsafe.
What size tank do Blackline Rasbora and Masked Julie (Julidochromis) 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 Masked Julie (Julidochromis) together?
Keep the aquarium between 23°C and 26°C. A target of around 24.5°C sits comfortably within both species' preferred ranges.
Are Blackline Rasbora or Masked Julie (Julidochromis) aggressive?
Blackline Rasbora is peaceful (1/10) and Masked Julie (Julidochromis) is moderately assertive (6/10). The gap in aggression levels means the calmer fish may experience stress from the more assertive one.
What pH do Blackline Rasbora and Masked Julie (Julidochromis) need?
Their pH requirements do not overlap. Blackline Rasbora prefers 6–7.5, while Masked Julie (Julidochromis) needs 8–9. This makes them incompatible in the same water chemistry.
How do I manage Masked Julie (Julidochromis)'s territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Masked Julie (Julidochromis) 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.
Related Comparisons
Blackline Rasbora & Copper Harlequin Rasbora
·
Blackline Rasbora & Glowlight Danio
·
Blackline Rasbora & Harlequin Rasbora
·
Blackline Rasbora & Neon Green Rasbora (Kubotai)
·
Blackline Rasbora & Pearl Danio
·
Blackline Rasbora & White Cloud Mountain Minnow
·
Masked Julie (Julidochromis) & Afra Cichlid
·
Masked Julie (Julidochromis) & African Jewel Cichlid
·
Masked Julie (Julidochromis) & Altolamprologus Calvus
·
Masked Julie (Julidochromis) & Altolamprologus Compressiceps
·
Masked Julie (Julidochromis) & Aurora Yellow Mbuna
·
Masked Julie (Julidochromis) & Black Diamond Cichlid
·