Goldfish and Neon tetra
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
- 400 L
- Minimum length
- 150 cm
- Factors considered
- 6
Concerns
Goldfish reaches about 35 cm and takes fish small enough to swallow. At roughly 3.5 cm, an adult Neon tetra is inside that range. This is usually discovered as fish quietly disappearing overnight rather than as visible aggression. Neon tetra is fusiform — the ordinary torpedo and Goldfish has a small terminal mouth, so Neon tetra stops being a possible mouthful SOONER than the usual rule suggests — at around 28% of Goldfish's length rather than 40%.
Derived from: traits.predation.smallFish, adultSize on both records, and the stored body form and gape of both
The shared band 20–22 °C sits at the top of one animal's range and the bottom of the other's. Both would be kept at their limits to accommodate the other. Both animals would be kept at the edge of their ranges to accommodate the other. Nothing here is a recommendation; it is the arithmetic of two incompatible requirements meeting at a point.
Derived from: environment.temperature range position on both records
pH ranges overlap only across 7–7.5, which is tighter than most tap-water supplies hold naturally.
Derived from: environment.ph overlap width
Why it can work
- Hardness requirements overlap at 8–10 °dGH.
- Neon tetra needs a group of at least 8. 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 8 Neon tetra, 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
Documented
Reported in husbandry or veterinary sources rather than derived from stored traits.
AquariumHQ's overall position
Incompatible, and the reason is thermal rather than behavioural. This is the pairing where the derived assessment and the documented evidence agree most completely, and where 'it worked for me' most often means one of the two animals was quietly being shortened.
Factor by factor
- TemperatureReported
The central problem, and it is not behavioural. A goldfish kept at tropical community temperatures has a shortened life; a neon tetra kept at goldfish temperatures is at the bottom of its range. There is no temperature at which both are correctly kept.
- Predation as the goldfish growsReported
An adult goldfish is large enough to take a neon tetra, and goldfish are opportunistic feeders.
- BioloadDerived
Goldfish produce substantially more waste than a community fish of comparable length, which is why goldfish stocking advice reads oddly to a tropical keeper.
| Depends on | How much |
|---|---|
| Tank size and dimensions | minor |
| Life stage | significant |
| The individual animal | none |
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 | Forced compromise — neither animal is where it wants to be | The shared band 20–22 °C sits at the top of one animal's range and the bottom of the other's. Both would be kept at their limits to accommodate the other. |
| pH | Forced compromise — neither animal is where it wants to be | The shared band 7–7.5 pH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other. |
| Hardness | Forced compromise — neither animal is where it wants to be | The shared band 8–10 °dGH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other. |
Forced compromise — neither animal is where it wants to be
Both animals would be kept at the edge of their ranges to accommodate the other. Nothing here is a recommendation; it is the arithmetic of two incompatible requirements meeting at a point.
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 | Evidence-backed | Forced compromise — neither animal is where it wants to be. The shared band 20–22 °C sits at the top of one animal's range and the bottom of the other's. Both would be kept at their limits to accommodate the other. Reported: The central problem, and it is not behavioural. A goldfish kept at tropical community temperatures has a shortened life; a neon tetra kept at goldfish temperatures is at the bottom of its range. There is no temperature at which both are correctly kept. |
| pH | Derived from stored traits | Forced compromise — neither animal is where it wants to be. The shared band 7–7.5 pH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other. |
| Hardness | Derived from stored traits | Forced compromise — neither animal is where it wants to be. The shared band 8–10 °dGH sits at the bottom of one animal's range and the top of the other's. Both would be kept at their limits to accommodate the other. |
| Body size | Derived from stored traits | Goldfish reaches about 35 cm against 3.5 cm for Neon tetra — a ratio of 10.0. Size disparity drives opportunistic predation independently of temperament. |
| Predation | Evidence-backed | Highest predation risk in either direction is "moderate". Reported: An adult goldfish is large enough to take a neon tetra, and goldfish are opportunistic feeders. |
| Territoriality | Derived from stored traits | Neither animal holds a territory. |
| Breeding aggression | Derived from stored traits | Neither becomes notably more aggressive while spawning. |
| Fin-nipping | Derived from stored traits | No nipper-and-target combination between these two. |
| Aggression | Derived from stored traits | Strongest intraspecific aggression across the pair is "none". It bears on the pairing because a fish under pressure from its own kind redirects. |
| Social requirements | Derived from stored traits | Neon tetra needs at least 8. 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 | Goldfish eats plants, which constrains the aquascape rather than the pairing. |
| Tank dimensions | Derived from stored traits | The more demanding of the two needs at least 400 L and 150 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: none. |
Environmental overlap
| Parameter | Shared range | Reading |
|---|---|---|
| Temperature | 20–22 °C | Aim for the middle of the shared band. |
| pH | 7–7.5 | Stability matters more than the exact figure. |
| Hardness | 8–10 °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 Goldfish or Neon tetra.
- 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.
Goldfish
No wild referent
variable flow · not characteristic oxygen
Neon tetra
Blackwater
shaded upper-Amazon tributaries, black and clear water mixed
8–40 µS/cm · low flow · moderate oxygen
- TemperatureGoldfish 10–22°CNeon tetra 20–26°C
Both inside their range from 20–22°C — 33% 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.
- pHGoldfish 7–8.5Neon tetra 4–7.5
Both inside their range from 7–7.5 — 33% 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.
- General hardnessGoldfish 8–25 dGHNeon tetra 1–10 dGH
Both inside their range from 8–10 dGH — 22% of the narrower animal’s range.
Barely an overlap. Whatever is chosen, at least one animal spends its life at the limit of its published range — which is survivable and is not the same as suitable.
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.