Bronze corydoras 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.
Should not be attempted. At least one factor is expected to cause harm.
- Minimum volume
- 405 L
- Minimum length
- 150 cm
- Factors considered
- 8
Concerns
Jack Dempsey reaches about 22 cm and takes fish small enough to swallow. At roughly 7 cm, an adult Bronze corydoras is inside that range. This is usually discovered as fish quietly disappearing overnight rather than as visible aggression. Jack Dempsey has a large — a piscivore's mouth and Bronze corydoras is depressed — flattened top to bottom, so the size at which Bronze corydoras stops being a possible mouthful is HIGHER than the usual third-of-body-length rule — around 62% of Jack Dempsey's length rather than 40%.
Derived from: traits.predation.smallFish, adultSize on both records, and the stored body form and gape of both
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
Temperature requirements overlap at 24–26 °C, though the band does not sit centrally for both animals. Aim for the middle of it and keep the heater accurate.
Derived from: environment.temperature on both records
Jack Dempsey defends a territory and both animals use the same part of the tank, so give the territory-holder a defensible area away from the main swimming space.
Derived from: traits.territoriality and zone on both records
Why it can work
- pH requirements overlap at 6.5–7.8.
- Hardness requirements overlap at 5–18 °dGH.
- Bronze corydoras needs a group of at least 6. Kept in smaller numbers it is not simply lonely — shoaling species held below their threshold show chronic stress behaviour, colour loss and, in several species, increased aggression towards tankmates.
- 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.
- At least 6 Bronze corydoras, counted as one group
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
Conditional on floor area and on what happens when the cichlid spawns. Outside breeding it is one of the more workable large-cichlid pairings; during breeding the corydoras need somewhere else to be, and a tank that cannot provide that is a tank where this fails.
What would change it: A footprint with two clearly separate floor zones, and a decision in advance about where the corydoras go when eggs appear.
Factor by factor
- Floor territory against a substrate feederReported
The Jack Dempsey claims floor and the corydoras live on it. The corydoras is not a rival and does not behave like one, which is why the pairing survives outside breeding and fails during it.
- Breeding aggressionReported
A spawning pair defends a radius that in most tanks is the whole floor. Corydoras eat eggs and are treated accordingly, and this is the point at which the arrangement usually ends.
- ArmourReported
Corydoras carry bony plates and a locking pectoral spine, which is why they survive this pairing more often than an unarmoured fish of the same size would. Survival is not the same as being unharassed.
| Depends on | How much |
|---|---|
| Tank size and dimensions | decisive |
| Life stage | significant |
| The individual animal | significant |
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 | Workable | The shared band 24–26 °C is usable, though it does not sit centrally for both animals. |
| pH | Comfortable for both | The shared band 6.5–7.8 pH sits centrally in both ranges, with room to drift. |
| Hardness | Comfortable for both | The shared band 5–18 °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 | Workable. The shared band 24–26 °C is usable, though it does not sit centrally for both animals. |
| pH | Derived from stored traits | Comfortable for both. The shared band 6.5–7.8 pH sits centrally in both ranges, with room to drift. |
| Hardness | Derived from stored traits | Comfortable for both. The shared band 5–18 °dGH sits centrally in both ranges, with room to drift. |
| Body size | Derived from stored traits | Jack Dempsey reaches about 22 cm against 7 cm for Bronze corydoras — a ratio of 3.1. Size disparity drives opportunistic predation independently of temperament. |
| 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 defends a radius that in most tanks is the whole floor. Corydoras eat eggs and are treated accordingly, and this is the point at which the arrangement usually ends. |
| 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 defends a radius that in most tanks is the whole floor. Corydoras eat eggs and are treated accordingly, and this is the point at which the arrangement usually ends. |
| Social requirements | Derived from stored traits | Bronze corydoras needs at least 6. A shoaling species held below its threshold shows chronic stress and, in several species, increased aggression towards tankmates. |
| Group-size dependency | Derived from stored traits | The outcome depends on group size as much as on the pairing: under-grouped shoalers nip more and hide more. |
| 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 | Jack Dempsey 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: significant. See the documented record. |
| Individual variation | Evidence-backed | Individual variation: significant. |
Environmental overlap
| Parameter | Shared range | Reading |
|---|---|---|
| Temperature | 24–26 °C | Aim for the middle of the shared band. |
| pH | 6.5–7.8 | Stability matters more than the exact figure. |
| Hardness | 5–18 °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 Bronze corydoras 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.
These two animals come from different kinds of water, and that is where the arithmetic below comes from rather than from anything about their temperaments.
Bronze corydoras
Lowland floodplain
40–300 µS/cm · still flow · low oxygen
Jack Dempsey
Hard alkaline water
300–900 µS/cm · moderate flow · moderate oxygen
- TemperatureBronze corydoras 22–26°CJack Dempsey 24–29°C
Both inside their range from 24–26°C — 50% of the narrower animal’s range.
A real window, and a narrow one. The tank has to be held inside it, and there is little room for the drift that happens between water changes.
- pHBronze corydoras 6–7.8Jack Dempsey 6.5–8
Both inside their range from 6.5–7.8 — 87% 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 hardnessBronze corydoras 2–18 dGHJack Dempsey 5–20 dGH
Both inside their range from 5–18 dGH — 87% 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.