Convict cichlid and Jack Dempsey
Can these two share a tank? The assessment below is derived from stored behavioural and environmental traits, not from a compatibility chart.
Workable only in unusual circumstances. Not a pairing to plan around.
- Minimum volume
- 450 L
- Minimum length
- 165 cm
- Factors considered
- 7
Concerns
Both animals hold strong territories. Two strongly territorial residents in one tank means continuous boundary pressure unless the footprint is large enough to give each an independent area with sightline breaks.
Derived from: traits.territoriality on both records
Convict cichlid becomes markedly more aggressive while spawning. A pairing that has been peaceful for months can change within a day, so plan for where the other animal goes if it does.
Derived from: traits.breedingAggression
Jack Dempsey becomes markedly more aggressive while spawning. A pairing that has been peaceful for months can change within a day, so plan for where the other animal goes if it does.
Derived from: traits.breedingAggression
Why it can work
- Temperature requirements overlap comfortably at 24–29 °C, with room for both animals to sit inside their preferred range.
- pH requirements overlap at 6.5–8.
- Hardness requirements overlap at 6–20 °dGH.
- The two occupy different levels of the tank, which reduces direct competition for space.
Conditions
Most interesting pairings are conditional on something. These are the things the keeper can actually change.
- A long tank with hardscape dividing it into visually separate territories
- At least 450 L with a footprint of 165 cm or more, before counting anything else in the tank
Derived, or documented?
These are different claims and are shown separately. The verdict above is derived from stored traits — arithmetic on AquariumHQ's own records. Whether the pairing is actually reported to work is a separate question, and for most pairs the honest answer is that we hold nothing.
Environmental compatibility
Derived from stored traits
Temperature, pH, hardness, size and behavioural traits compared between the two records. Sound as far as it goes, and it is not evidence that the pairing works.
Behavioural evidence
Widely reported in practice
Reported consistently across aquarium practice without a single citable source. Treated as real but not as measurement.
AquariumHQ's overall position
A pairing whose outcome depends almost entirely on the individual fish and on how much ground there is. Two Central Americans with no chemistry conflict and a permanent territorial one, and the smaller fish is not reliably the loser.
What would change it: Footprint and broken sightlines. Removing the convicts' spawning site removes most of the problem and most of the convicts' behaviour with it.
Factor by factor
- Breeding aggression from the convictReported
A spawning pair of convicts holds ground against fish several times their size, and the reports of them dominating much larger Central Americans are consistent. Size is not the deciding variable here.
- Predation on convict fryDerived
A Jack Dempsey eats convict fry, which convicts produce continuously. The pairing generates a constant supply of conflict for exactly that reason.
- WaterDerived
Both Central American, both hard water, both tolerant. Nothing here is a chemistry problem.
| Depends on | How much |
|---|---|
| Tank size and dimensions | decisive |
| Life stage | minor |
| The individual animal | decisive |
How good is the overlap?
Whether two ranges intersect is a necessary condition, not evidence. What matters is WHERE the shared band sits: an overlap at the top of one animal's range and the bottom of the other's is a forced compromise however wide it looks, and it is the case a simple intersection test cannot see.
| Dimension | Assessment | What that means here |
|---|---|---|
| Temperature | Comfortable for both | The shared band 24–29 °C sits centrally in both ranges, with room to drift. |
| pH | Comfortable for both | The shared band 6.5–8 pH sits centrally in both ranges, with room to drift. |
| Hardness | Comfortable for both | The shared band 6–20 °dGH sits centrally in both ranges, with room to drift. |
Factor by factor
Every factor states what it rests on. Most are derived from the traits stored on both records — sound arithmetic on AquariumHQ's own data, and not a report about how the pairing actually goes. Where a factor says 'not known', the data is missing and saying so matters, because a missing factor and a favourable one look identical once both are absent.
| Factor | Basis | Finding |
|---|---|---|
| Temperature | Derived from stored traits | Comfortable for both. The shared band 24–29 °C sits centrally in both ranges, with room to drift. |
| pH | Derived from stored traits | Comfortable for both. The shared band 6.5–8 pH sits centrally in both ranges, with room to drift. |
| Hardness | Derived from stored traits | Comfortable for both. The shared band 6–20 °dGH sits centrally in both ranges, with room to drift. |
| Body size | Derived from stored traits | Adult sizes are comparable at about 15 cm and 22 cm, so neither is a mouthful for the other. |
| Predation | Derived from stored traits | Highest predation risk in either direction is "near-certain". |
| Territoriality | Derived from stored traits | Strongest territoriality across the pair is "strong". |
| Breeding aggression | Evidence-backed | Breeding aggression reaches "strong". A pairing peaceful for months can change within a day of a spawn. Reported: A spawning pair of convicts holds ground against fish several times their size, and the reports of them dominating much larger Central Americans are consistent. Size is not the deciding variable here. |
| Fin-nipping | Derived from stored traits | No nipper-and-target combination between these two. |
| Aggression | Evidence-backed | Strongest intraspecific aggression across the pair is "strong". It bears on the pairing because a fish under pressure from its own kind redirects. Reported: A spawning pair of convicts holds ground against fish several times their size, and the reports of them dominating much larger Central Americans are consistent. Size is not the deciding variable here. |
| Social requirements | Derived from stored traits | Neither animal requires a group. |
| Group-size dependency | Derived from stored traits | The outcome does not depend on group size for either animal. |
| Tank zone | Derived from stored traits | The two use different levels of the tank, which reduces direct competition for space. |
| Activity level | Derived from stored traits | Activity levels are compatible. |
| Food competition | Derived from stored traits | Different feeding strategies, so direct competition is limited. |
| Risk to shrimp and snails | Derived from stored traits | Highest risk either animal poses to dwarf shrimp or snails is "near-certain". |
| Effect on plants | Derived from stored traits | Convict cichlid uproots plants, which constrains the aquascape rather than the pairing. |
| Tank dimensions | Derived from stored traits | The more demanding of the two needs at least 300 L and 120 cm of length before anything else is in the tank. Volume alone does not describe a home for a fish that swims in straight lines. |
| Life stage | Evidence-backed | Life-stage dependency: minor. See the documented record. |
| Individual variation | Evidence-backed | Individual variation: decisive. |
Environmental overlap
| Parameter | Shared range | Reading |
|---|---|---|
| Temperature | 24–29 °C | Aim for the middle of the shared band. |
| pH | 6.5–8 | Stability matters more than the exact figure. |
| Hardness | 6–20 °dGH | Check your source water before committing. |
What this assessment cannot tell you
- Individual temperament varies, particularly in cichlids and in bettas, and can override a favourable verdict for Convict cichlid or Jack Dempsey.
- The assessment is for the pair in isolation. A third species can change the outcome in either direction.
- Both animals are assessed at adult size, not at the size they are sold.
- A verdict is a statement about probability, not a guarantee.
Where the two water bands meet
Derived from the ranges AquariumHQ publishes for each species. The compatibility engine reads the same numbers; this is what they look like drawn on one axis.
Temperature (°C)
Scale: 0 to 36 °C.
pH (pH)
Scale: 4 to 9.5 pH.
Hardness (°dGH)
Scale: 0 to 30 °dGH.
Why the bands sit where they do
The overlap above is arithmetic. This is where the two numbers came from — the kind of water each animal is recorded from, and how much room that leaves.
Both animals come from hard alkaline water, which is why the bands below sit where they do.
Convict cichlid
Hard alkaline water
300–900 µS/cm · moderate flow · moderate oxygen
Jack Dempsey
Hard alkaline water
300–900 µS/cm · moderate flow · moderate oxygen
- TemperatureConvict cichlid 21–29°CJack Dempsey 24–29°C
Both inside their range from 24–29°C — 100% of the narrower animal’s range.
A wide window. Both animals are inside their own range across most of it, and the tank can be run without either sitting at an edge.
- pHConvict cichlid 6.5–8Jack Dempsey 6.5–8
Both inside their range from 6.5–8 — 100% of the narrower animal’s range.
A wide window. Both animals are inside their own range across most of it, and the tank can be run without either sitting at an edge.
- General hardnessConvict cichlid 6–25 dGHJack Dempsey 5–20 dGH
Both inside their range from 6–20 dGH — 93% of the narrower animal’s range.
A wide window. Both animals are inside their own range across most of it, and the tank can be run without either sitting at an edge.
Computed from the ranges AquariumHQ publishes for each species, each of which records what it rests on — a source value, a habitat inference, a physiological requirement or a trade convention. Most are habitat inferences, and the species pages say which.