Leporinus affinis

A 30 cm Amazon headstander for a large aquarium

Leporinus affinis is a freshwater headstander from the Amazon River basin in South America. FishBase places it in the family Anostomidae and records a maximum length of 30 cm total length. It is a fish for a keeper with a large, long aquarium, sturdy companions and a plan for a diet built around plant matter.

It is easy to misjudge. It sits with the larger tetras in our own range, but Wikipedia groups it with the toothed headstanders rather than the tetras, and the adult is many times the length of a typical tetra. Buy it for the aquarium it will need at full size, not for the size it arrives at.

In the wild, FishBase notes that adults live in sand holes in fast-flowing creeks and feed on plants, fruits and leaves. It classes the species as benthopelagic, a fish of the lower and middle water rather than strictly the bottom, and lists it as Least Concern on the IUCN Red List.

For a keeper with a large South American set-up, that makes it a striking fish for the open water between the floor and the midwater, with the bold banding shown in the gallery. For anyone with a standard community tank, it is a fish to admire rather than buy.

Quick facts

Is it right for you?

Answer yes to all four before buying:

• Can your aquarium, now or by the time it grows, give a 30 cm fish a long run of open water?
• Are your current or planned companions robust, similar in size and short-finned?
• Will you feed a plant-based staple rather than relying on flake alone?
• Can you keep to a weekly water change and test, every week?

What one purchase brings

Each purchase supplies one live Leporinus affinis in the size you choose from the selector: 3–4 cm, 4–5 cm, 5–7 cm or 8–10 cm. The size you select is the size supplied, not the adult size. Even the largest choice is about a third of the 30 cm FishBase records, so every option needs the same long-term plan.

Choosing a size

Pick the size that suits your filter as well as your tank. A smaller fish adds less waste at first, which gives a newly matured filter time to grow with it; an 8–10 cm fish brings more waste from the first day and belongs in an aquarium whose filter already supports other fish. None of the sizes changes the adult you are planning for.

For more than one fish, raise the quantity: each unit is a single fish of the chosen size. Read the group planning in the compatibility tab before you do, because every extra fish is another potential 30 cm adult.

No size comes with a chosen sex. Sex is guaranteed only when the selected option explicitly states male or female. This Leporinus affinis listing has no sex-guaranteed option.

The gallery shows fish with bold black vertical bands on a pale, cream-yellow body, alone and in a pair. Gallery images have been digitally enhanced to improve image quality. Natural colour, pattern, size and maturity can vary between live animals.

If your aquarium is sized for small shoaling fish, browse our tetra range for species that stay small instead; it holds many fish far better matched to a standard community tank. If you do have the space, the care tab sets out everything to prepare before this fish arrives.

Give it the space a 30 cm fish needs

Plan the aquarium for a 30 cm adult from the day you buy. That is the maximum total length FishBase records for the species, and it is far beyond the fish that most small community tanks are built for.

OATA's care sheet for tetras and pencilfish shows why the usual tetra rules do not stretch this far. It notes that most tetras stay between 2 and 5 cm, with some larger species nearer 10 cm, and recommends at least an 80 litre aquarium for the larger species of 5 cm and over. Those figures describe fish a fraction of the length of an adult Leporinus, so treat them as a floor for small fish, not a guide for this one.

How the sizes compare with 30 cm

What “large enough” means in practice

• Length first: OATA asks for space to swim, and for a fish heading for 30 cm that means a long run of open water, so favour a long tank over a tall one.
• Room to turn: the front-to-back depth must let a 30 cm fish turn without brushing the decor.
• Stability: OATA advises buying an aquarium as large as possible within reason, because a larger volume keeps temperature and water quality more stable.
• All the fish at once: size the tank for every fish in it at adult size, not for the juveniles you start with.

Why “upgrade later” rarely works

Buying a juvenile for a smaller tank and planning to move it on sounds simple, but a new aquarium needs its own matured filter, and OATA warns that stocking a tank too quickly can cause new tank syndrome. Moving a large fish into an immature system repeats the risks of arrival day at a larger scale. Setting up the final aquarium first avoids that step entirely.

If you are unsure whether your aquarium is big enough, measure its length, depth and height and send us the figures before you order. It is far kinder to plan now than to rehome a grown fish later.

Aim for 23–27 °C and pH 6.5–7.8

Hold the water at 23–27 °C, pH 6.5–7.8 and 4–12 dGH. FishBase records the species in a natural environment of 23–27 °C, pH 5.8–7.8 and up to 20 dH. OATA’s tetra and pencilfish sheet, written for those groups as a whole rather than this species, suggests 22–27 °C, pH 6.5–8.0 and 4–12 °dH. The routine targets below are where the two meet, so an aquarium set inside them sits within both.

The wider FishBase figures, down to pH 5.8 and up to 20 dH, describe where the species has been recorded in nature. Keep them as background rather than settings to chase; a steady value inside the table does more for the fish than a number pushed towards either extreme.

Working out your nitrate ceiling

Test your tap water first. If it reads 15 mg per litre, the aquarium should stay at or below 35 mg per litre under OATA’s rule; if it reads zero, keep the tank at 20 or less. A large, plant-eating fish produces plenty of waste, so this is the number most likely to creep up between water changes.

Holding the temperature

Use a heater with a thermostat sized for the full aquarium volume, and set it to one value inside 23–27 °C. Check it against a separate thermometer every day at feeding time, so a failed heater or a stuck thermostat is caught within hours rather than days.

Matching your tap water

If your conditioned tap water already sits inside pH 6.5–7.8 and 4–12 dGH, routine water changes will keep the aquarium there with no extra work. If it sits outside, find out before you buy rather than after: large weekly changes then pull the tank towards your tap values every time, which is the opposite of the stability this fish needs.

Tools that help

Our aquarium water parameters guide explains what each test tells you, and the water parameter matcher compares your readings with a target range so you can see at a glance whether your tap water suits before the fish arrives.

A weekly routine that keeps a big fish healthy

Change water weekly and test weekly. OATA’s maintenance advice for tetras and pencilfish is the routine to follow here, and its reasoning matters even more with a fish that grows this large.

1. At least once every week, make a partial water change of 25%, using a siphon to lift solid waste from the gravel or sand.
2. Test at least once per week so ammonia and nitrite never build up unnoticed.
3. Treat replacement water with tap water conditioner to remove chlorine or chloramine before it goes in.
4. Check the filter for blockages. When the media needs cleaning, do not run it under the tap; rinse it lightly in the tank water taken out during the water change.

The last step protects the beneficial bacteria in the filter, which chlorine or chloramine may kill. The RSPCA puts it plainly: no fish should be kept without a well set up and maintained filter. Fish release ammonia, which is toxic; the bacteria turn it into nitrite, also toxic, and then into nitrate, which is safer.

Planning water changes in a big tank

A quarter of a large aquarium is a lot of water. Have a hose or siphon long enough to reach a drain, enough conditioner for the whole replacement volume, and a way to bring the new water close to tank temperature. A routine that is easy to carry out is one you will keep up every week.

Choosing the filter

Size the filter for the full aquarium and for the fish at adult size, not for a 3–4 cm juvenile. Choose a model you can open and check without draining the tank, since OATA asks for regular checks for blockages, and remember that the media must be rinsed in tank water rather than under the tap.

Before the first fish goes in

Mature the filter first. Our guide to setting up a tropical tank covers cycling step by step, so ammonia and nitrite already read zero on arrival day. OATA stresses that these fish can be stressed by even the smallest amounts of ammonia, which is why a fully matured filter matters more than any piece of decor.

Scaling the routine as it grows

A 3–4 cm juvenile adds little waste; a fish several times that length adds much more. Keep the same weekly rhythm, watch the nitrate trend, and increase the frequency of partial changes if readings climb towards your ceiling.

Sand, open water and decor that survives a plant-eater

Use sand or gravel on the floor and leave plenty of open water. FishBase records adults living in sand holes in fast-flowing creeks, and OATA’s sheet calls for aquarium gravel or sand plus space to swim.

Cover without clutter

OATA recommends live plants for cover, or plastic plants and ornaments such as plant pots and model caves where live plants are not used. Put the cover along the back and sides and keep the middle and front open, so a long fish can swim the full length of the tank.

Plants and a plant-eating fish

FishBase notes that this species feeds on plants, fruits and leaves, so soft aquarium plants may be treated as food. If you want greenery that lasts, lean on sturdy or artificial plants and ornaments, and regard any soft plants as a bonus rather than the backbone of the layout.

Water movement

Its wild home in fast-flowing creeks suggests it copes with lively water, so a well-sized filter with a steady outflow is a sensible choice. Keep a calmer corner behind decor for resting, and make sure the flow does not scour the sand bare.

A layout that works

In a long aquarium, bank sturdy or artificial plants and a piece of wood along the back third, set a cave or large plant pot at each end, and leave the centre and front as open sand. The fish gets shelter at both ends and a clear lane to swim between them, and you get an unobstructed view of it across the tank.

• Floor: sand or fine gravel.
• Cover: sturdy or artificial plants, pots and caves at the back and sides.
• Open water: the full length of the tank clear for swimming.
• Flow: steady movement with a quieter resting area.

Build the diet around plant matter

Make plant matter the base of the diet. FishBase records that this species feeds on plants, fruits and leaves in the wild, so plant-based foods should be its staple rather than an occasional extra.

OATA’s tetra sheet adds useful support for variety. It describes these groups as omnivorous fish that take most food types, recommends a good quality flake or granule, and suggests small live or frozen foods such as daphnia, small bloodworm or tubifex. Use those as supplements around the plant-based core.

How much to feed

Feed only what the fish can eat within a few minutes, once a day, as OATA advises. Uneaten food breaks down and releases toxic waste into the water, and a large fish can leave a lot behind if it is overfed.

• Staple: plant-based foods sized to the fish’s mouth.
• Variety: good quality flake or granules.
• Extras: small live or frozen foods such as daphnia.
• Check: nothing left on the floor a few minutes after feeding.

Adjusting as it grows

A 3–4 cm juvenile needs small pieces it can take easily; an 8–10 cm fish handles noticeably larger food. Move up a food size as it grows rather than simply adding more small food, and watch body shape: a thin fish needs a little more, a noticeably round one less.

In a tank with other robust fish, make sure it gets its share. Scatter food across the open water so faster feeders cannot take it all in one place.

Arrival day, step by step

Prepare before you order: OATA advises confirming that ammonia and nitrite read zero before any new fish goes in, and building stock numbers up slowly.

Our team hand-packs each fish, bagged in pure oxygen inside an insulated box, adding a heat pack when the weather calls for it. A licensed live-animal courier carries the parcel, and we email tracking with your confirmed delivery date so you know when to be home. The full terms are on our delivery and Live Arrival Guarantee page.

When the parcel comes

1. Be there to receive it; live fish cannot be left unattended.
2. Start a continuous unboxing video while the parcel is still sealed, with the outer box in view.
3. Carry on filming in one take as you open it, until the fish is visible inside its sealed bag.
4. Float the bag in your aquarium for 20–30 minutes to acclimatise the fish slowly.
5. Release the fish and never pour the bag water into your tank.
6. If something is wrong, contact us the same day with your order number and the video; WhatsApp is the fastest route, and we will arrange a replacement or refund.

For the Live Arrival Guarantee, someone must be at the address to receive the parcel, it must be opened and inspected on the day it arrives, and the continuous video must start from the sealed parcel.

Once the fish is released, the first month plan below takes over.

Your first month with a young Leporinus

Use the first month to settle the fish and learn its normal. OATA explains that stocking too quickly can cause new tank syndrome, when there are too few nitrifying bacteria for the extra waste and ammonia and nitrite rise to unhealthy levels, so this is a period for watching rather than adding.

Hold any new additions until the readings have stayed steady through the month. When you do add fish, add them one at a time and repeat the same watchful week after each one.

Feed lightly at first. Uneaten food breaks down into toxic waste, as OATA warns, and in a young system that shows up as ammonia quickly. Increase towards a full portion as the fish clears its food within a few minutes and the readings stay at zero.

Spot problems early

Know what healthy looks like. OATA lists clear bright eyes, undamaged fins, intact scales, no ulcers or bumps and normal swimming as the signs of a healthy fish; check for them on arrival and at every feed.

Changes to act on

Every fish varies a little, so learn this one’s normal pattern during the first week: how it moves, where it rests and how eagerly it feeds. A change from that pattern is the signal, not a single odd moment.

First response

Test the water first, as OATA advises whenever you are concerned about a fish’s health. Correct any ammonia, nitrite or nitrate problem with partial water changes using conditioned water. If the signs persist, contact us with your readings and a description of what you are seeing.

Keep notes

A line a day in the first weeks, covering feeding, behaviour and test results, makes changes easy to spot and gives useful detail if you ever need advice. OATA’s point that these fish can be stressed by even the smallest amounts of ammonia is a good reason to log every reading, not just the worrying ones.

Handling

Move a large fish calmly. Guide it into a net or container rather than chasing it around the tank, and keep the time out of water as short as possible.

Sexing and breeding

Do not expect to tell males from females at purchase. OATA notes that most fish are difficult to sex unless they are breeding, and even the largest size offered is only about a third of adult length.

In the wild, FishBase records that distinct pairs breed in densely grown, weedy places. That is a description of natural behaviour rather than a home-breeding method, and spawning is not something to plan around when buying.

For most keepers the sex of the fish makes little practical difference. The aquarium, the diet and the choice of companions are the same whichever you receive, and the space needed is set by the 30 cm adult length.

• At purchase: sex cannot be chosen.
• In the wild: pairs spawn among dense weed.
• In the aquarium: plan the tank around the adult size, not a breeding project.

Choosing tank mates for a large, active fish

Choose robust fish of a similar size and temperament. OATA’s sheet says tetras and pencilfish mix best with species of a similar size and temperament to themselves, and because Leporinus affinis outgrows the tetras that sheet describes, it is the sheet’s rules for larger fish that apply.

Two rules to follow

• No small fish it could eat: OATA says small species such as neon tetras or Beckford’s pencilfish should not be kept with any fish large enough to eat them. A fish heading for 30 cm grows far larger than a neon tetra, so follow this rule from the start.
• No timid or long-finned fish: OATA says the larger or more boisterous species should not be kept with timid or long-finned fish, as they may nip their fins.

Screen each candidate

• Size: close to the adult size of this fish, not just its size on arrival.
• Temperament: confident and active rather than shy.
• Fins: short and sturdy rather than long and flowing.
• Water: comfortable at 23–27 °C and pH 6.5–7.8.
• Space: the whole group fits the aquarium once every fish is grown.

Juveniles change the picture over time. A 3–4 cm fish is small enough to look at home among small species, but it will not stay that size, so choose companions for the adult from the start rather than rearranging the community later.

Water and diet as filters too

A good companion also shares the 23–27 °C, pH 6.5–7.8 range and will not strip the tank of the plant foods this fish depends on. Feeding a mixed community is easier when every fish accepts the same flake or granules, with the plant-based staple added for the Leporinus.

If the mix goes wrong

Watch the whole community, not just the Leporinus. Split or ragged fins on a tank mate, a fish hiding more than normal, or rising aggression are the temperament and appearance changes OATA asks keepers to look for. Test the water first, then rethink the mix before the fish grow any further.

Stock gradually, whatever you choose. Adding fish slowly lets the filter bacteria keep pace, as OATA advises for every new addition.

How many to keep, and how to plan a group

Let the aquarium decide the number. OATA’s advice to keep tetras and pencilfish in groups of at least five is written for those small shoaling families, which mostly stay under 10 cm. Applied to a fish that reaches 30 cm, a group of five would need an exceptionally large aquarium.

A practical way to plan

1. Measure the aquarium and picture every fish at its adult length, not its size on arrival.
2. Count the other large fish you keep or plan to keep, since they share the same open water.
3. Start with the number the tank can hold at adult size, and add fish one at a time.
4. Watch temperament and water readings after each addition before adding more.

A worked example

Say your aquarium can comfortably hold two fish of around 30 cm alongside its other residents. Start with one Leporinus and your robust companions, let a month of steady readings pass, then add the second. If readings climb or temperament changes, stop there: the tank has shown you its limit.

If you are unsure how many your tank can take, send us its dimensions and a list of the fish already in it before ordering, and we can talk through a realistic plan with you.

Common questions

How big does Leporinus affinis grow?

FishBase records a maximum length of 30 cm total length for the species. Plan the aquarium for that adult size, whichever size you buy, because the size supplied is only a starting point.

What size aquarium does it need?

Plan for a 30 cm adult in a long tank with open swimming space, sand or gravel and cover at the ends. OATA asks for at least 80 litres even for tetras over 5 cm, most of which stay under 10 cm, so this fish needs a far larger aquarium than that.

How many should I keep together?

Let the aquarium decide. The groups of at least five OATA advises are for small tetras and pencilfish; with a fish that reaches 30 cm, keep only as many as the tank can hold at adult size and add them one at a time.

Is Leporinus affinis suitable for beginners?

It suits a keeper who can already provide a large, mature aquarium more than a first tank. It reaches 30 cm and needs steady water quality, plant-based feeding and carefully chosen tank mates, so a keeper with experience of large fish will find it far easier.

What does it eat?

Base the diet on plant matter, since FishBase records it feeding on plants, fruits and leaves. Add good quality flake or granules and small live or frozen foods such as daphnia, feeding what it clears within a few minutes, once a day.

What temperature and pH does Leporinus affinis need?

Keep it at 23–27 °C and pH 6.5–7.8, where FishBase's recorded environment for the species overlaps OATA's tetra guidance, with general hardness of 4–12 dGH.

Is it aggressive, and will it nip fins?

Treat it as a large, active fish. OATA advises that larger or more boisterous fish in this group should not share a tank with timid or long-finned fish, as they may nip their fins, so choose short-finned, confident companions.

Which fish can live with Leporinus affinis?

Robust fish of a similar size and temperament that suit 23–27 °C water and have short fins. OATA says small species such as neon tetras should not be kept with any fish large enough to eat them, and this one grows to 30 cm.

How does Leporinus affinis arrive alive in the UK?

Start filming a continuous unboxing video while the parcel is still sealed. The fish travels hand-packed in oxygen with a licensed live-animal courier. Float the bag for 20–30 minutes before releasing it, and send us the video with your order number the same day if anything has gone wrong.

Further reading

• FishBase: Leporinus affinis, for family, distribution, recorded water environment, maximum length, wild habitat, diet, breeding pairs and IUCN status.
• Wikipedia: Leporinus affinis, for the family Anostomidae, the toothed headstanders, and the Amazon River basin range.
• OATA: how to look after tetras and pencilfish, for water guidance, aquarium set-up, maintenance, feeding portions, compatibility rules and health signs.
• RSPCA: fish environment, for why every aquarium needs a working filter and how ammonia becomes nitrite and nitrate.