Rummy Nose Tetra (Petitella rhodostoma)

Know the fish and the offer

Rummy Nose Tetra is the familiar trade name for Petitella rhodostoma, a small freshwater tetra from South America. FishBase places it in Acestrorhamphidae and records it from the lower Amazon and Orinoco river basins. Older aquarium literature may use Hemigrammus rhodostomus, but both names may therefore appear when you research this fish.

This is a peaceful, active shoaling fish rather than a solitary centrepiece. Its close group movement is most effective when the aquarium gives the shoal a clear route to travel. The species suits a keeper prepared to provide a long, mature aquarium, stable warm water and a group of at least 10. Browse the wider tetras collection if you are comparing different shoaling fish before deciding.

Choose the dispatch grade carefully

One purchase quantity supplies one animal of the selected option. The size you select is the size supplied, not the adult size. Use the live size selector for the choices shown when ordering, then plan every option around the same adult needs described below.

Sex is guaranteed only when the selected option explicitly states male or female. This Rummy Nose Tetra listing has no sex-guaranteed option.

Some gallery images are representative, based on reference photographs of this species, and none shows the exact animal supplied, so colours can look slightly different from the live animal.

Before selecting an arrival date, read our current delivery and Live Arrival Guarantee policy for the applicable schedule, receiving steps and claim process.

Plan the aquarium around the adult size and water

Seriously Fish gives 50 mm standard length for this species, while FishBase records a maximum of 5 cm total length for male or unsexed fish. Use 5 cm as the practical upper planning reference rather than treating a dispatch measurement as the finished size.

Small body size does not make this a static nano fish. Its active swimming behaviour calls for an aquarium at least 90 cm long, and it should be kept in a group of 10 or preferably more. Aquarium length, open swimming space and the needs of the whole shoal are therefore more useful decisions than choosing a tank from the length of one juvenile.

Use these core planning values

The 24–27°C, pH 5.5–7.0 and 2–15 dGH ranges are routine aquarium guidance for this fish. Measure the aquarium before purchase rather than trying to alter every value at once. Stability within the working ranges is the goal, and alkaline conditions may cause the fish's colour to fade.

Check the overall fit

A well-planted layout can work, as can a simpler arrangement based on sand, wood, roots and dried leaves. Both approaches must preserve the long swimming route that the group needs. The decisive fit is therefore a mature 90 cm or longer aquarium with compatible water, adequate filtration and room for at least 10 fish—not merely an aquarium that can physically contain one small tetra.

Give the shoal enough length and company

Plan the group and aquarium together. This fish should be maintained in a shoal numbering at least 10, with more preferred, and it is known for swimming in a comparatively close formation. A solitary fish or token group does not meet that instruction, even if the water values are otherwise suitable.

Begin by measuring the usable aquarium length. A nominally large aquarium with a short footprint is not equivalent to a tank at least 90 cm long because this species needs distance for active swimming. Wood, roots, plants and ornaments also reduce the open route, so assess the finished layout rather than the empty glass box.

Work through the space decision

1. Confirm at least 90 cm of aquarium length. Do this before using volume or external dimensions as a shortcut.
2. Reserve a continuous swimming lane. The shoal should be able to travel and turn without weaving through dense decoration at every point.
3. Count the intended group. Start the plan at 10 fish and include any fish already kept as the same species.
4. Allow for every other resident. The tetra group is only one part of the aquarium's biological load and space use.
5. Plan from the adult reference. Use up to 5 cm per fish for long-term decisions, regardless of the dispatch grade selected.

For example, selecting a 2–2.5 cm fish does not reduce the 90 cm length or group requirement. Ten fish from that dispatch band remain a plan for ten adults of up to 5 cm. The smaller measurement describes the fish at dispatch; it is not permission to use a shorter aquarium or postpone the group indefinitely.

If a 90 cm aquarium is already crowded with active residents, adding 10 more fish may create competition even though each tetra is small. In that case, reduce the existing stocking plan or choose a different aquarium rather than squeezing the shoal into the remaining space. If the aquarium is long enough but decoration fills the centre, move tall planting and bulky wood towards the rear or ends to recover a clear route.

More than 10 can produce a stronger group display, but only when filtration, swimming room and the total community can support the extra waste and activity. “More is preferred” is not an instruction to exceed the aquarium's safe capacity.

Match the water before changing it

Target 24–27°C, pH 5.5–7.0 and 2–15 dGH for routine aquarium care. Test the aquarium and tap water first, write down the results, then decide whether the fish fits. Our water chemistry guide explains what the common readings mean, while the water matcher helps compare measured values with this range.

Read the three values together

One matching number cannot compensate for two mismatches. Water at 25°C still needs a suitable pH and hardness, and a pH of 6.8 does not resolve a temperature outside 24–27°C. Check potential companions against the same three values so the aquarium can be run to one coherent plan.

Do not chase an exact midpoint through repeated abrupt adjustments. A reading of pH 6.8 already sits within 5.5–7.0; changing it merely to reach a preferred-looking number adds instability without improving the match. The same reasoning applies to temperature and hardness when they are already inside their stated ranges.

Alkaline conditions may cause the fish's colour to fade. Treat fading as a prompt to measure pH alongside ammonia, nitrite, nitrate and temperature rather than diagnosing the cause by appearance alone. Colour can vary, and water tests give you values on which you can act.

If your water falls outside the ranges, decide on a controlled water-management method before the fish is introduced. Any replacement water then needs to follow the same plan at every water change. A one-off correction followed by unsuitable tap water each week creates repeated movement in chemistry.

Record baseline readings before adding the group, then compare future tests with that baseline. This makes a trend visible: a small repeated movement in pH or a rising waste reading is easier to address early than after behaviour and feeding have changed.

Mature the filter before adding the group

A functioning biological filter is essential. The RSPCA explains that fish release toxic ammonia; beneficial filter bacteria convert it to nitrite, which is also toxic, and then to the safer nitrate. A filter must therefore be established and maintained, not simply switched on when fish arrive.

OATA's tetra and pencilfish advice gives broad group guidance: ammonia and nitrite should each be 0 mg per litre, nitrate should not exceed 20 mg per litre above the normal tap-water level, and the water should be tested at least weekly. Use those waste limits alongside the 24–27°C, pH 5.5–7.0 and 2–15 dGH values for this fish.

Confirm readiness in the right order

1. Prepare and mature the filter. Follow our first tropical aquarium guide before adding livestock.
2. Test ammonia and nitrite. Both readings need to be 0 mg per litre before the group is introduced.
3. Measure nitrate against the tap-water baseline. Keep it within 20 mg per litre above that starting level.
4. Check temperature, pH and hardness. Confirm all three suit the tetra at the same time.
5. Assess the existing population. Beneficial bacteria need time to respond whenever fish numbers and feeding increase.

Adding a group of 10 represents a meaningful rise in waste production. A filter that supports a lightly stocked aquarium today may need time to accommodate that increase. Stocking too quickly can produce new tank syndrome when the bacterial population cannot process the added waste.

Check the filter for blockages and maintain its water flow. When filter media needs cleaning, do not run it under the tap. Rinse it lightly in aquarium water removed during a water change.

Filtration and water testing answer different questions. The filter processes waste, while tests show whether that process is keeping pace. Use both: clear-looking water alone does not show whether ammonia or nitrite is present.

Build cover without blocking the swimming route

Choose between two supported layout styles: a natural-looking arrangement based on river sand, wood, roots and dried leaves, or a more standard planted aquarium. The fish can do well in either, provided the finished design includes shelter and a long open route for the shoal.

Natural-style arrangement

• Use river sand as the substrate.
• Add driftwood branches and twisted roots without filling the central swimming lane.
• Add a few handfuls of suitable dried leaves for a natural feel.
• Allow wood and leaves to tint the water like weak tea if that effect suits the aquarium plan.
• Remove old leaves and replace them every few weeks so they do not rot and foul the water.
• Use fairly dim lighting.

Beech can be used as wood only when thoroughly dried and stripped of bark. Suitable dried beech or oak leaves may be used for leaf litter. Aquarium-safe peat in a small net bag within the filter is another described way to help create blackwater conditions, but any water adjustment still needs measurement against pH 5.5–7.0 and 2–15 dGH.

Planted arrangement

A well-planted aquarium is a valid alternative even though aquatic plants are not a feature of the species' natural waters. Place taller or denser planting where it creates cover without dividing the tank into narrow passages. Keep a broad front or central corridor open so the group can travel together.

If live plants are not used, suitable artificial plants and aquarium ornaments can provide shelter. Whatever materials you choose must leave the minimum 90 cm tank length useful to the fish. A 90 cm aquarium whose entire front is blocked by wood is not functioning like a 90 cm swimming route.

Smaller tetras benefit from a gentle current, but they should still have places where swimming is comfortable. Watch the group after introduction: if every fish is repeatedly confined to one low-flow corner, review the direction of the outlet and the placement of decoration. Do not reduce filtration simply to reduce current; redirect the flow while preserving biological filtration.

Feed small foods in one controlled meal

Rummy Nose Tetra is omnivorous and accepts a wide range of aquarium foods, but its small mouth determines the useful particle size. Build the routine around a quality flake or small granule, then add suitably small live or frozen foods for variety.

Build a practical feeding plan

Offer a measured amount and watch the entire shoal, not only the quickest fish. The species is peaceful and may not compete well with very boisterous or much larger companions. If food disappears before the group can feed, the first correction is to review the community and food distribution rather than continually increasing the total amount.

Small particles should be easy for the fish to take. Break an unsuitable large flake into smaller pieces or choose a smaller granule instead of expecting the fish to manage food that does not match its mouth. Remove or reduce any item that repeatedly reaches the substrate uneaten.

A varied mixture of dried and small live or frozen foods supports the best colour development. Variety does not mean adding several full portions in one day. Rotate suitable foods across the routine while keeping the total daily amount within what the group finishes in a few minutes.

Uneaten food breaks down and adds toxic waste to the water. If leftovers remain after a meal, remove what you can, reduce the next portion and include ammonia, nitrite and nitrate in the next test. When body condition falls or interest in food changes, compare the observation with water readings and competition at feeding time before altering the whole diet.

Introduce the fish without outrunning the filter

Prepare the aquarium before the fish arrive. Confirm a temperature of 24–27°C, pH 5.5–7.0 and hardness of 2–15 dGH, with ammonia and nitrite each at 0 mg per litre. The filter should already be mature and running normally, and the planned group needs a tank at least 90 cm long.

Before introduction

• Measure the aquarium rather than relying on its model name.
• Confirm that the intended group is at least 10 fish.
• Test temperature, pH, hardness, ammonia, nitrite and nitrate.
• Check filter flow and clear any blockage without replacing established media unnecessarily.
• Leave an open swimming route through the finished decoration.
• Screen existing residents for size, temperament, feeding competition and matching water needs.

Increase the aquarium's population slowly because beneficial filter bacteria need to respond whenever fish numbers and feeding rise. A group of 10 small fish still represents additional waste. If other fish were added recently, allow the aquarium to stabilise and confirm the waste readings before making the next increase.

First-week checkpoints

Keep observations specific. “The fish look different” is less useful than recording that several fish remained at the surface after feeding or that one fish was excluded from the group. Pair each change with measured water values and the time it occurred.

Do not judge compatibility only by the absence of immediate chasing. Peaceful fish may still lose access to food beside larger or more forceful residents. Watch feeding and use of the swimming lane throughout the settling period.

Use a weekly routine to catch changes early

At least once every week, carry out a partial water change of 25%. Test the water at least weekly as well, with ammonia and nitrite held at 0 mg per litre and nitrate kept no more than 20 mg per litre above the normal tap-water level. Treat replacement tap water with conditioner to remove harmful chlorine or chloramine before it enters the aquarium.

Weekly maintenance sequence

1. Observe before disturbing the aquarium. Note swimming position, breathing, colour, hiding and interest in food.
2. Test the water. Record ammonia, nitrite and nitrate, then include temperature and the chemistry values relevant to your water-management plan.
3. Change 25%. Use a siphon to remove solid waste from the substrate where needed.
4. Condition replacement tap water. Keep the change consistent with the aquarium's temperature and chemistry plan.
5. Inspect the filter. Check for blockages and rinse dirty media lightly in removed aquarium water when cleaning is needed.
6. Review the record. Compare the readings and observations with previous weeks instead of treating each result in isolation.

Watch for hanging at the surface, sitting on the bottom, erratic swimming, darker or paler colour, increased hiding, altered breathing, white spots, fluffy growths, fin or scale loss, bumps, ulceration, changes in body condition or reduced feeding. These signs are prompts for investigation, not a diagnosis by themselves.

If behaviour or appearance changes, test the water first and inspect the filter. A non-zero ammonia or nitrite result requires immediate attention to water quality and the recent stocking or feeding load. If the readings are within plan, review aggression, food competition and any recent environmental change.

The red head may become less vivid in alkaline conditions, but colour alone should not be treated as a water test. Check pH and the waste readings before deciding what has changed. Avoid rapid chemistry adjustments made only from visual appearance.

If you are concerned about an ongoing health change, record the readings and observations, then contact us for further guidance. Do not add a treatment simply because several conditions can produce a similar sign.

Screen every tank mate for size and temperament

This is a very peaceful tetra that may lose out beside very boisterous or much larger fish. Avoid any fish large enough to eat it. For every other candidate, screen adult size, temperament, feeding behaviour, water needs and use of swimming space before relying on a common “community fish” label.

Use a four-part compatibility screen

Seriously Fish names other Hemigrammus and Hyphessobrycon tetras, pencilfish, Apistogramma dwarf cichlids, Corydoras and small loricariids as possible South American companions. Smaller rasboras, barbs, anabantoids and West African dwarf cichlids such as Pelvicachromis are also described for broader communities. These are candidates for screening, not universal promises: each species and aquarium must still pass the four questions above.

Adult size matters more than the size seen at purchase. A young companion that cannot swallow the tetra today may become unsafe as it grows. Compare the planning size of every resident, not just the measurements shown by juvenile fish.

Temperament includes access to food. A fish need not attack the shoal to be a poor match; repeatedly taking every bite first can leave peaceful tetras underfed. Watch a complete meal and confirm that the whole group feeds without being displaced.

Space is also shared. Bottom-oriented companions still add waste and may need their own floor area, while midwater fish may occupy the same route as the shoal. Count all residents against the mature filter and finished layout before deciding that different swimming levels solve capacity.

Make the whole community fit one water plan

Compatibility fails when different residents require conflicting care, even if they behave peacefully. Build one written plan covering 24–27°C, pH 5.5–7.0, hardness of 2–15 dGH, ammonia and nitrite at 0 mg per litre, and nitrate no more than 20 mg per litre above the tap-water baseline. Every species in the aquarium must fit that plan.

Worked screening examples

• Peaceful but too large: avoid a fish whose adult size makes a 5 cm tetra potential prey.
• Small but boisterous: use caution if it repeatedly displaces the shoal from food or open water.
• Calm but chemically mismatched: do not combine it when its required temperature, pH or hardness conflicts with the tetra's range.
• Matching water but crowded aquarium: do not add the group until at least 10 have adequate swimming room and the filter can support the total load.
• Named companion from a compatibility list: still check the exact species, adult size, temperament and water needs.

For example, a candidate that suits 25°C and pH 6.8 passes two water checks, but it must also tolerate the measured hardness and remain too small to eat the tetra. It must then pass the behaviour, food and space checks. Compatibility is the result of all those decisions, not one matching value.

The same rule applies when adding more tetras. A larger shoal can strengthen the group display, but extra fish increase waste and use more of the swimming lane. More than 10 is preferable only within the capacity of the aquarium and filter.

Observe the community at feeding time and during normal swimming. If the shoal is repeatedly pushed away from food, confined to a corner or hiding more than usual, reassess the dominant residents and layout. Pair those observations with water tests so a behavioural concern is not confused with a chemistry problem.

When comparing two possible companions, choose the one that matches the water plan, remains safe at adult size and feeds without overwhelming this peaceful tetra. If neither passes every screen, keep the shoal with fewer companion species rather than forcing a mixed community.

Answer the key questions before choosing

What is the Rummy Nose Tetra?

Petitella rhodostoma is a peaceful freshwater shoaling tetra from the lower Amazon and Orinoco river basins, reaching up to 5 cm.

Does one purchase supply one Rummy Nose Tetra?

One purchase supplies one animal of the selected size option, so set the purchase quantity to the number of fish required for the planned group.

Which dispatch sizes can I choose?

The dispatch grades are 2–2.5 cm, 3–3.5 cm, 3.5–4 cm and XL; use the live size selector for the choices shown when ordering.

What aquarium does the Rummy Nose Tetra need?

Use a mature aquarium at least 90 cm long, with an open swimming route, an established filter and enough capacity for the full community.

How many Rummy Nose Tetras should live together?

Keep a group of at least 10 fish, with more preferred only when the aquarium, swimming space and filter can support the additional load.

What water values should I use?

Keep it at 24–27°C, pH 5.5–7.0 and 2–15 dGH, with ammonia and nitrite at 0 mg per litre.

What does a Rummy Nose Tetra eat?

Feed quality flake or small granules with suitably small live or frozen foods, once daily and only in an amount eaten within a few minutes.

How should I acclimate it?

Before introduction, confirm 24–27°C, pH 5.5–7.0, 2–15 dGH and 0 mg per litre ammonia and nitrite, then increase the aquarium population slowly so the mature filter can respond.

Which companions suit this fish?

Choose peaceful fish that cannot eat or outcompete it, share 24–27°C, pH 5.5–7.0 and 2–15 dGH, and leave enough room for a shoal of at least 10.

References used for identity and care

• FishBase, Petitella rhodostoma: accepted identity, family, freshwater environment, distribution and maximum recorded length.
• Seriously Fish, Hemigrammus rhodostomus: aquarium length, group size, water ranges, layout, feeding and compatibility guidance.
• Ornamental Aquatic Trade Association, tetras and pencilfish: group husbandry covering filtration, waste limits, feeding, introduction, maintenance and compatibility screening.
• RSPCA aquarium environment guidance: biological filtration and the conversion of ammonia through nitrite to nitrate.
• Tropical Fish Co delivery policy: current delivery schedule, receiving information and Live Arrival Guarantee terms.