Compatibility brief
Can Dwarf pencilfish live with Jack Dempsey?
Risky. This mix is commonly discouraged for typical setups.
Dwarf pencilfish + Jack Dempsey: Aggression mismatch. Jack Dempsey is aggressive, while Dwarf pencilfish is peaceful. The aggressive fish will likely bully or harm the peaceful one. Real tanks add variables Fishori cannot model; treat this as a high-risk read, not certainty.
Compatibility score
Profile confidence: medium
Order of checkstank volume vs adults → predation mouth gap → temperament / fin nipping → shared water windows.
200L
Combined minimum footprint reference for these two species: about 200L (larger active fish often want more length).
Jack Dempsey (25cm adult) may treat small Dwarf pencilfish (~3.5cm) as food once grown — plan adult sizes, not shop sizes.
Dwarf pencilfish (peaceful) and Jack Dempsey (aggressive) are far apart on aggression — bullying or injury is a common outcome in average community layouts.
Assessment details
Aggression mismatch
Top issueJack Dempsey is aggressive, while Dwarf pencilfish is peaceful. The aggressive fish will likely bully or harm the peaceful one.
Jack Dempsey may eat Dwarf pencilfish
Jack Dempsey (25cm) is predatory and Dwarf pencilfish (3.5cm) is small enough to be eaten. This pairing is unsafe.
Compatible temperature range
Both fish can comfortably share similar water temperatures.
Narrow pH overlap
These fish can share water but their ideal pH ranges overlap only slightly. Aim to keep pH stable in the shared range.
“Jack Dempsey is aggressive, while Dwarf pencilfish is peaceful”
Aggression mismatch
Next steps
Concrete changes, not "research more" filler.
- •Dwarf pencilfish should be kept in a group of at least 8 for best health and behaviour.
Try instead
- →Dwarf pencilfish should be kept in a group of at least 8 for best health and behaviour.
- →Build a species-only tank for the larger fish, or restock with fish too large to be eaten at adult sizes.
- Seriously Fish. Nannostomus marginatus
Primary: aquarium size, water chemistry, behaviour, and compatibility (URL verified in upgrade script; recheck if site content changes).
- FishBase. Nannostomus marginatus
Secondary: taxonomy, distribution, and maximum length in nature; cross-check with aquarium import lines and measured tank parameters.
- Wikipedia. Nannostomus marginatus
Secondary: general species context; verify all husbandry numbers against a dedicated aquarium care sheet and your test kit, not a single table row.
- Seriously Fish. Rocio octofasciata
Primary: aquarium size, water chemistry, behaviour, and compatibility (URL verified in upgrade script; recheck if site content changes).
- FishBase. Rocio octofasciata
Secondary: taxonomy, distribution, and maximum length in nature; cross-check with aquarium import lines and measured tank parameters.
- Wikipedia. Rocio octofasciata
Secondary: general species context; verify all husbandry numbers against a dedicated aquarium care sheet and your test kit, not a single table row.
Try this next
Build the full stocking list with Dwarf pencilfish + Jack Dempsey
Plan further
Try both species in the full-stock tank check, or open either fish profile for mates lists. Methodology explains how verdicts are produced.
Individual fish vary in personality. Fishori uses conservative hobby rules. Observe any new introduction closely, feed thoughtfully, and keep a quarantine or backup plan. This is not veterinary advice.
Profile data confidence: high. Based on multiple reputable aquarium care sources with strong agreement.