Buenos Aires Tetra (Psalidodon anisitsi) – 3.5–5.5cm Sizes

Identify the fish and choose the right option

The Buenos Aires Tetra (Psalidodon anisitsi) is a freshwater ray-finned fish from South America. FishBase places it in Acestrorhamphidae among the American tetras and records it from the Paraná and Uruguay River basins. It reaches a recorded maximum of 13.2 cm total length. Wikipedia identifies the Buenos Aires Tetra as a South American freshwater member of the same family.

This fish suits a keeper who can maintain a shoal of at least five, provide a mature filtered aquarium and avoid timid or long-finned companions. It is a larger, boisterous tetra rather than a choice for a community built around quiet fish or trailing fins.

The 13.2 cm figure is a maximum record, not a promise that every individual will reach exactly that length. It is still the safer figure around which to plan swimming room, filtration capacity and companion size. Do not treat the dispatch size as a permanent adult size.

Choose by dispatch size

The size you select is the size supplied, not the adult size. Both choices refer to the same species, and the live size selector is where you choose the required dispatch size. Increasing the purchase quantity increases the number of individual fish; it does not turn one unit into a pair or a ready-made shoal.

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

The gallery images are representative, based on reference photographs of this species, so colours can look slightly different from the live animal.

Prepare the aquarium and planned group before choosing a quantity. For packing, dispatch arrangements and guarantee conditions, read the current delivery and Live Arrival Guarantee policy.

Check the decisive care numbers before buying

OATA’s tetra and pencilfish guidance gives 22–27°C, pH 6.5–8.0, general hardness of 4–12°dH and carbonate hardness of 3–10°dKH for the group. It also requires zero ammonia, zero nitrite and nitrate no more than 20 mg per litre above the normal tap-water level. Use these as group guidance rather than a species-specific optimum, and choose one stable point that also suits every intended companion.

OATA recommends at least 80 litres for larger tetra species measuring more than 5 cm. Because FishBase records this fish at up to 13.2 cm total length, the larger-tetra figure is the appropriate starting point. Treat 80 litres as a planning floor for a small shoal, not an automatic capacity for unlimited companions. Aquarium shape, usable swimming room, filter capacity and the eventual size of every fish still determine whether a proposed community is sensible.

Tetras are shoaling fish. Keep at least five, with more being better when the aquarium and filter can carry the extra adult load. A single fish or an undersized group will often become stressed. Plan the social group and the biological load together rather than choosing the fish count from litres alone.

Decide whether this tetra fits

Use the numbers as a connected plan

An 80-litre aquarium with a mature filter may be a starting point for the required shoal, but it is not automatically suitable for a heavily stocked mixed community. A larger aquarium normally gives more swimming room and makes temperature and water quality easier to keep stable. Leave open water for movement while providing shelter around the edges, then reserve filter capacity for the complete adult community.

This tetra suits a keeper who can maintain a shoal, test the water every week and screen companions for temperament and fin shape. Choose another aquarium plan if the intended community depends on timid fish or long, trailing fins.

Hold the water within the working range

Keep the aquarium between 22 and 27°C, with pH between 6.5 and 8.0. General hardness should remain within 4–12°dH, while carbonate hardness should be 3–10°dKH. These are ranges within which to choose a stable operating point, not a sequence of values through which the aquarium should move.

Start by testing the tap water and the established aquarium. Use the water chemistry guide to understand what pH, general hardness, carbonate hardness, ammonia, nitrite and nitrate measure. The water matcher can then help compare measured aquarium values with the working ranges used here.

Prioritise toxic-waste readings

Ammonia and nitrite must be zero because both are toxic. Nitrate should not exceed 20 mg per litre above the level already present in normal tap water. Measure the tap-water baseline rather than treating 20 mg per litre as a universal final reading. For example, if the tap water measures 10 mg per litre nitrate, the stated ceiling is 30 mg per litre in the aquarium; if the tap water measures 25 mg per litre, the corresponding ceiling is 45 mg per litre.

Stability matters because every intended companion must live at the same temperature and in the same chemistry. Compare requirements before combining species, then maintain one suitable point rather than pushing the aquarium towards opposite ends of the range for different fish. Record readings taken at the same stage of the weekly routine so changes are easier to recognise.

Do not alter several values at once in response to a single unusual test. Repeat the measurement correctly, check temperature and filtration, and compare it with the normal pattern for that aquarium. A measured response protects the fish from abrupt changes while addressing the value that actually needs attention.

Mature the filter before adding the shoal

A working biological filter is essential. The RSPCA explains that fish release toxic ammonia and that beneficial bacteria in a well-set-up filter convert it first to toxic nitrite and then to safer nitrate. A mature aquarium is therefore one in which the filter is processing waste reliably, not simply one that has contained water for a particular number of days.

Prepare and mature the aquarium before livestock is introduced. If this is your first setup, follow the first tropical aquarium guide, then confirm with tests that ammonia and nitrite are both zero. Do not use clear-looking water as a substitute for those readings; dissolved toxic waste can be present without making the aquarium visibly dirty.

Match filtration to the full plan

• Count the whole shoal: at least five fish create more waste than one fish, even when the individuals are still within a small dispatch size.
• Count every companion: filter capacity must cover the complete community rather than this species in isolation.
• Plan for growth: the selected dispatch band is temporary, while the recorded maximum reaches up to 13.2 cm total length.
• Allow bacterial capacity to adjust: increase the aquarium population slowly rather than making a large, unplanned jump in waste and feeding.
• Keep the filter running effectively: check for blockages and reduced flow as part of routine maintenance.

Overstocking or increasing the population too quickly can leave too few nitrifying bacteria to process the extra waste. This can produce unhealthy ammonia and nitrite levels associated with new tank syndrome. The correct preventive action is to plan the intended group before purchase, mature enough filtration for that load and keep testing as the aquarium population changes.

Filter capacity is not a reason to ignore swimming room. A powerful unit cannot turn an undersized aquarium into suitable accommodation, just as a large aquarium cannot remain healthy without effective biological filtration. Volume, open space, shelter, adult stock and waste processing must work together.

Before adding the shoal, confirm that the filter is operating normally, temperature is within 22–27°C and both ammonia and nitrite read zero. If any of those checks fails, correct the aquarium first. This protects the fish and avoids placing extra waste into a system that is already struggling.

Build space for swimming and shelter

Start with an aquarium of at least 80 litres for the small shoal and assess how much of that volume remains usable after substrate, ornaments and equipment are installed. The recorded maximum of up to 13.2 cm total length makes adult planning essential. A dispatch-size fish still needs accommodation designed for later growth and for the movement of the entire group.

Use aquarium gravel or sand as the substrate. Provide shelter with live plants where appropriate, or use plastic plants and suitable ornaments such as plant pots or model caves. These features give fish places to move out of view, but they should not consume all of the swimming area. Arrange cover around open water rather than filling every part of the aquarium with solid decoration.

Balance each part of the layout

A nominal 80-litre volume is only a starting point. Two aquariums with the same stated volume can provide different amounts of practical swimming room once their shapes and decoration are considered. Choose the layout that gives the group both an open route and places of refuge. More volume also tends to make temperature and water quality more stable.

Assess the aquarium after decorating it. Look from end to end and identify whether the fish can move through the main water area without meeting a solid barrier at every turn. Then check that shelter is spread across more than one point, so access is not limited to a single ornament.

Plan all companions before deciding that spare-looking water is genuinely spare capacity. Fish sharing a similar swimming area compete for the same room even when the filter can process their waste. Bottom, middle and upper positions can help organise a community, but they do not cancel the need to assess adult size, temperament and total biological load.

Keep a proper shoal without overloading the aquarium

Keep Buenos Aires Tetras in a group of at least five. More is better when the aquarium has enough volume, swimming room and established filtration for the extra adult load. Tetras kept singly or in groups that are too small will often become stressed, so one fish should not be treated as a complete long-term social plan.

Work backwards from the adult community. First account for the tetra shoal, then add every established or intended companion to the calculation. Compare their expected sizes, water ranges, temperaments and swimming needs. Finally, decide whether the filter and water-change routine can keep ammonia and nitrite at zero after feeding increases.

Resolve common stocking conflicts

• The aquarium can house only one or two: choose a different stocking plan rather than maintaining an undersized tetra group.
• The filter is newly matured: confirm zero ammonia and nitrite and avoid increasing the population faster than its bacterial capacity can adjust.
• The aquarium already has many fish: calculate the complete adult load before adding a shoal, even when open water appears empty.
• You want more than five: increase the group only where swimming space, filtration and water quality can support more fish.
• Several fish must be introduced: prepare biological capacity beforehand instead of relying on corrective maintenance after waste rises.

Purchase quantity and social requirement are separate decisions. Each purchase represents one fish of the selected size, while the welfare plan calls for at least five in the aquarium. The required quantity therefore depends on how many compatible Buenos Aires Tetras already live in suitable accommodation, not on whether an image happens to show one or two animals.

Observe the group after any stocking change. Changes in aggression, hiding, swimming position, breathing, colour, body condition or feeding interest can indicate that the fish are under pressure. Check water quality first, then reassess space, group number and the temperament of companions.

Do not use a larger group as a guaranteed cure for every behavioural problem. More fish also mean more waste and less space per individual. The better decision is the largest sensible shoal that the mature aquarium can support while maintaining stable water and suitable separation from timid or long-finned fish.

Feed once a day with controlled variety

FishBase records worms, crustaceans, insects and plants in the wild diet. For aquarium feeding, OATA’s tetra guidance treats the group as omnivorous. Use a good-quality flake or granule as the main aquarium food and add variety with small live or frozen items such as daphnia, small bloodworm or tubifex. Choose pieces that the fish can take readily rather than offering food that is too large for the individuals in the selected dispatch size.

Feed once a day and offer only what the shoal can consume within a few minutes. This instruction controls both nutrition and water quality: uneaten food breaks down and releases waste into the aquarium. A large portion is not a substitute for watching whether every fish has had access.

Judge the portion by the whole group

1. Add a modest amount of the chosen food.
2. Watch whether the shoal notices it and feeds without food accumulating on the substrate.
3. Check that less assertive individuals can reach some of the portion.
4. Stop when the amount that can be eaten within a few minutes has been offered.
5. Reduce the next portion if food remains, then review water quality if leftovers have been breaking down.

Rotate suitable food types rather than making every portion richer or larger. Flake or granules provide a consistent base, while small live or frozen foods add variety. The instruction remains one controlled daily feed, not separate full meals for every food type.

Avoid repeatedly adding food to test a fish that has lost interest. Reduced feeding can be an early health or water-quality warning. Look for changes in breathing, colour, swimming, hiding and body condition, then test ammonia, nitrite, nitrate and temperature.

Keep feeding consistent enough that changes are meaningful. If the same measured amount is normally eaten readily but suddenly remains, that contrast provides a useful signal. Record the food offered alongside test results when investigating a change.

Introduce the fish only to a ready aquarium

Complete the aquarium preparation before the fish are introduced. The tank should be large enough for the planned shoal, contain a functioning filter, provide open swimming room and shelter, and hold water within 22–27°C, pH 6.5–8.0 and the stated hardness ranges. Test ammonia and nitrite immediately before stocking; both must be zero.

Before introduction

• Confirm that the biological filter is operating and has been matured for livestock.
• Check temperature, ammonia, nitrite and nitrate rather than relying on appearance alone.
• Make sure gravel or sand, shelter and open swimming space are already arranged.
• Review the complete community for adult size and temperament.
• Prepare for a group of at least five without exceeding the aquarium’s capacity.

Increase the aquarium population slowly. Beneficial bacteria need to increase as more fish are added and feeding rises. If stocking grows more quickly than the filter can respond, ammonia and nitrite may reach unhealthy levels. A planned shoal does not remove the need to consider the filter’s current load.

First-week checkpoints

During the first month, continue the same weekly tests and 25% partial water changes carried out at least once a week. Compare each result with earlier readings. If ammonia or nitrite appears, pause any further stocking and address water quality rather than assuming the filter will catch up without intervention.

Healthy fish should have clear, bright eyes, undamaged fins, intact scales and no ulcerations or bumps. Use those visible checks alongside swimming, breathing, temperament, body condition and feeding. A fish can look outwardly intact while water quality is changing, which is why observation and testing belong together.

Do not judge success from the first feeding alone. The useful measure is whether water remains stable and the shoal maintains normal movement, feeding and condition through repeated checks. Keep a short record of tests, maintenance and notable changes so a developing pattern is easier to act upon.

Maintain the aquarium every week

Carry out a 25% partial water change at least once a week. A siphon can remove solid waste from accessible areas of gravel or sand while the water is withdrawn. Treat replacement tap water with conditioner to remove harmful chlorine or chloramine before it enters the aquarium.

Test the water at least weekly. Ammonia and nitrite must remain zero, and nitrate must stay no more than 20 mg per litre above the normal tap-water level. Take the readings as part of a consistent routine so a change can be compared with the aquarium’s usual pattern.

Protect the biological filter

• Check the filter for blockages or an unexplained reduction in flow.
• If cleaning is needed, rinse the media lightly in aquarium water removed during the partial water change.
• Do not rinse established media under the tap, because chlorine or chloramine may kill beneficial bacteria.
• Return the cleaned media promptly and confirm that the filter resumes normal operation.
• Test the water after any disruption that could affect waste processing.

The weekly water change, substrate cleaning and filter check perform different jobs. Replacing water controls dissolved waste; siphoning removes solid debris; the filter processes ammonia and nitrite. Do not replace one task with another or strip the filter so thoroughly that its bacterial population is lost.

Respond to changes early

If you are concerned about a health change, test the water and contact us with the results, the aquarium temperature, recent maintenance and the signs observed. Do not choose a treatment from one symptom alone; first establish whether water quality or a husbandry change is contributing.

Keep the maintenance routine proportionate and consistent. Overfeeding, rapid stocking or a blocked filter can increase waste between weekly changes, so correct the cause as well as restoring the water. Stable results and unchanged behaviour are stronger indicators than a tank that merely looks clear.

Screen every companion before mixing species

Buenos Aires Tetras are among the larger or more boisterous tetras covered by OATA’s guidance. Avoid keeping them with timid or long-finned fish because they may nip fins. This is the decisive exclusion rule: a companion should not be chosen simply because both animals are commonly placed in community aquariums.

Tetras mix best with species of a similar size and temperament. Treat that as a screening rule rather than a universal tank-mate list. Compatibility remains conditional on adult size, behaviour, shared water requirements, aquarium volume, swimming room, group number and the total load on the filter.

Assess the aquarium, not just two names

Begin with the water overlap. Both species must be comfortable at one stable temperature between 22 and 27°C and within the stated chemistry. Next compare adult size and temperament. Then calculate whether the aquarium provides enough swimming space and whether the mature filter can handle both groups at their later size.

Use the current tetra collection to compare identities and care requirements, not to assume that every tetra belongs in the same community. Family or trade-group similarity does not cancel differences in size or behaviour.

For a stocking and compatibility assessment, contact us with the aquarium volume, current fish, measured temperature, pH and hardness, and the number of Buenos Aires Tetras planned. Include adult sizes rather than dispatch sizes wherever possible. That information allows the proposed community to be assessed as one system.

If the aquarium already contains timid or long-finned fish, choose a different stocking plan. Extra food, decoration or a larger shoal should not be used to override the supported avoidance rule.

Act when behaviour shows the mix is failing

Compatibility must be monitored after the initial decision because fish can vary in behaviour. Watch for increased aggression, unusual hiding, loss of feeding interest, changes in body condition, damaged fins, altered swimming or a fish remaining away from the group. These signs require action even when the community appeared suitable on paper.

Use an if-this-then-that check

Water-quality trouble can resemble a compatibility problem because it may change swimming, breathing, colour, temperament and feeding. Test first whenever several animals show a change at the same time. Ammonia or nitrite above zero requires immediate attention to water quality and filtration, regardless of how the fish interact.

When damage or persistent intimidation centres on a timid or long-finned companion, follow the avoidance rule and end that combination. Do not wait for repeated fin loss or declining body condition. Any alternative accommodation must itself be mature, filtered and suitable for the fish moved into it.

A shoal of at least five supports the tetra’s social requirement, but group number is only one part of compatibility. Adding fish to a crowded aquarium can increase waste and competition. Increase the shoal only where the aquarium can carry the additional adults while keeping water stable.

Review the community again as fish grow. A combination formed around small dispatch sizes may use much more space later, and FishBase’s maximum record reaches up to 13.2 cm total length. Preserve open swimming room and reassess total stocking before every addition.

The most reliable community plan is conservative: a proper shoal, companions of similar size and temperament, shared water values, adequate volume and a mature filter. Where one of those conditions changes, repeat the screen rather than relying on the aquarium’s earlier history.

Answer the key questions before choosing

How big does a Buenos Aires Tetra get?

The Buenos Aires Tetra reaches a FishBase-recorded maximum of 13.2 cm total length. Plan the aquarium around that adult figure rather than its 3.5–5.5 cm dispatch size.

What size aquarium does a Buenos Aires Tetra need?

Start with at least 80 litres for a small shoal. OATA gives this minimum for larger tetra species over 5 cm; provide a mature filter, shelter and open swimming room, then allow additional capacity for every companion.

How many Psalidodon anisitsi should I keep together?

Keep at least five. OATA’s tetra guidance says these shoaling fish will often become stressed when kept singly or in groups that are too small, and more is better where aquarium space and filtration allow.

Is the Buenos Aires Tetra suitable for beginners?

It suits a prepared keeper who can maintain at least five in a mature filtered aquarium, test the water weekly and avoid timid or long-finned companions. Its adult size and boisterous behaviour require planning.

What does this fish eat?

FishBase records worms, crustaceans, insects and plants in its wild diet. OATA recommends good-quality flake or granules once a day, limited to what the fish eat within a few minutes, with small daphnia, bloodworm or tubifex for variety.

What temperature and pH does a Buenos Aires Tetra need?

OATA’s tetra guidance gives 22–27°C, pH 6.5–8.0, general hardness of 4–12°dH and carbonate hardness of 3–10°dKH. Keep ammonia and nitrite at zero and choose a stable point within those group ranges.

Is it aggressive or likely to nip fins?

This fish is one of the larger or more boisterous tetras covered by OATA’s guidance and may nip fins. Avoid timid or long-finned fish, and act if you see persistent hiding, damaged fins or loss of feeding access.

Which animals can live with the Buenos Aires Tetra?

Consider fish of a similar size and temperament only after checking shared water requirements, adult stocking, swimming room and filtration. Avoid timid or long-finned fish; no named companion is an automatic match.

How does it arrive alive in the UK?

Someone must be present to receive the parcel. Film every delivery continuously from the sealed parcel as it is opened, keeping the fish in the sealed bag in view; float the bag for 20–30 minutes before releasing the fish, and never pour the bag water into the aquarium.

Consult the primary references

• FishBase species summary: accepted identity, family, environment, distribution, diet, aquarium behaviour and recorded maximum length.
• Wikipedia’s Buenos Aires Tetra article: general classification and South American occurrence.
• OATA tetra and pencilfish guidance: UK group husbandry, water, aquarium, feeding, maintenance and compatibility advice.
• RSPCA aquarium welfare guidance: biological filtration and nitrogen-cycle welfare principles.
• Tropical Fish Co delivery policy: packing, arrival procedure and Live Arrival Guarantee terms.