Rosy Danio (Danio roseus) – 2–5cm Size Grades

Choose an active Rosy Danio shoal

Rosy Danio is Danio roseus, a peaceful, active freshwater fish in the danio family Danionidae. FishBase lists its distribution across the Mekong basin in Thailand, Laos and Myanmar and records a maximum of 3.8 cm standard length. It suits a keeper who wants lively schooling movement and can provide a mature, covered community aquarium with enough horizontal room for at least 8–10 fish.

Plan the aquarium around the complete adult group rather than body length alone. The Seriously Fish species page gives a different length reference of 5.5 cm standard length and sets a smallest base of 90 × 30 cm, equivalent to about 81 litres. Use that footprint when planning swimming space while retaining the FishBase maximum of 3.8 cm as the adult-size figure throughout this profile.

We rate the care level as easy when the aquarium is already mature, filtered and large enough for the complete group. The essential work is straightforward but cannot be skipped: hold stable water within 18–25°C, pH 6.0–7.5 and 2–15 dGH; keep ammonia and nitrite at zero; use a tightly fitting cover; and make sure every fish feeds.

Use these figures for the first decision

Check whether the species fits your plans

A tall aquarium with the same litre label may offer less horizontal swimming room. Mixed communities also need capacity for every adult resident, so the 81-litre figure is a starting point for the Rosy Danio group rather than a universal stocking allowance.

Select the dispatch grade and quantity

Each unit supplies one Rosy Danio. The live size selector shows 2–2.5 cm, 2.5–3 cm and 3.5–5 cm sizes; select the required size and set the quantity to the number of fish you intend to keep.

The size you select is the size supplied, not the adult size. The selected measurement describes the fish at dispatch and does not reduce the adult aquarium footprint, stocking allowance or social-group requirement. Even the smallest fish needs an aquarium planned for at least 8–10 Rosy Danios and a base of at least 90 × 30 cm.

Turn the offer into a responsible group

1. Select the size: use one of the measured size bands shown by the live selector.
2. Set the quantity: each unit represents one animal, so a planned group of ten requires a quantity of ten.
3. Check the mature aquarium: confirm a base of at least 90 × 30 cm, a tightly fitting cover and sufficient filtration for the entire adult community.
4. Compare every resident: keep the chosen temperature, pH and hardness within the shared range of all animals in the aquarium.

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

Seriously Fish notes that females tend to grow larger and become deeper-bodied, particularly when gravid, but appearance must not be treated as a sex promise. Build the group without depending on a particular sex ratio.

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

If you are comparing this danio with other choices, browse the rasbora and danio collection and assess each animal by its own adult size, group requirement and water range. Read the delivery and Live Arrival Guarantee policy before the delivery date so someone is ready to receive the parcel and follow the arrival procedure.

Count the aquarium’s existing adult residents before setting the quantity. Ten Rosy Danios in an 81-litre planning aquarium do not automatically leave room for ten further tank mates; decor, swimming room, filter capacity and the needs of the complete community still determine final stocking.

Build a covered, planted swimming space

Start with an aquarium base of at least 90 × 30 cm or an equivalent footprint, with about 81 litres as the associated planning volume. Horizontal room matters because Rosy Danios are active schooling fish. A taller aquarium does not replace useful length if its base is shorter, and hardscape should not consume the open area needed by the complete group.

Fit a very tight cover before the fish arrive. Members of this genus are accomplished jumpers and can pass through surprisingly small gaps. Check spaces around cables, pipework, filter returns and feeding openings rather than judging the lid only from the centre. Close every opening through which a small fish could pass with aquarium-safe fittings.

Divide the aquarium into useful zones

A heavily planted arrangement with a darker substrate can show the fish effectively, while sparse decor may make their colour appear paler. Plants are useful for cover and presentation, but colour alone is not a health measurement. Keep enough open water to see whether each fish swims, feeds and holds condition normally.

A river- or stream-inspired layout can use variably sized rocks, gravel, water-worn boulders, driftwood roots and branches. Plants attached to decor can preserve more open substrate than dense planting across the whole base. Position every item securely and leave access to areas where solid waste settles.

Use a powerhead or filter outlet only to create controlled circulation. Avoid torrent-like conditions because small danios tend to occupy calmer stretches and marginal zones. Watch the complete group after adjusting an outlet: the layout should provide movement without forcing every fish to work continuously against the strongest current.

The finished aquarium should combine security with visibility. Cover around the margins lets nervous fish move away from disturbance, while the open centre allows the keeper to count the group and notice changes in swimming, appetite or body condition.

Establish filtration before the group arrives

Use a fully established biological filter before introducing Rosy Danios. RSPCA aquarium guidance explains that fish release toxic ammonia, which beneficial filter bacteria convert first to toxic nitrite and then to safer nitrate. A filter is life-support equipment rather than an optional way to make the water look clear.

If this is a new aquarium, follow our first tropical tank guide and mature the system before livestock arrives. Clear water alone does not show that the biological filter can process waste. Test ammonia and nitrite and proceed only when both remain at zero under the aquarium’s planned routine.

Match the filter to the planning aquarium

For an aquarium of about 81 litres, Seriously Fish uses a turnover of four to five times the volume each hour and points to a filter rated around 325–405 litres per hour. Position the outlet so it circulates the aquarium without turning the open swimming zone into a torrent.

• Before arrival: confirm the filter runs continuously, the aquarium is mature and ammonia and nitrite are zero.
• When planning the group: account for all 8–10 or more Rosy Danios and every existing adult resident.
• After additions: test the water because increased fish waste and feeding increase the work required from the bacterial population.
• If a test rises: stop further stocking and correct the water-quality problem before adding more animals.

Stocking too quickly can cause new tank syndrome when nitrifying bacteria cannot process the increased waste. The social requirement does not make an immature filter safe; prepare biological capacity for the intended group before purchase rather than using the fish to mature the aquarium.

Keep open access to the filter intake, outlet and media chamber. Check for blockages as part of routine maintenance, but do not leave the aquarium without circulation for unnecessary periods. The filter must support both waste processing and useful movement through the decorated footprint.

Judge filtration by measured water quality and fish behaviour together. Surface hanging, rapid breathing or erratic swimming requires an immediate water test even when the equipment appears to be running.

Hold stable water inside the species range

Keep Rosy Danios within 18–25°C, pH 6.0–7.5 and 2–15 dGH. These are species-level aquarium ranges from Seriously Fish. Choose a stable point inside them that also suits every other aquarium resident; the lower and upper limits are boundaries for screening, not a reason to move repeatedly between the extremes.

OATA’s broader danio guidance gives 17–27°C, pH 6.5–8.0, 4–12 dGH and 3–10 dKH for the group, with ammonia and nitrite at zero and nitrate no more than 20 mg per litre above the normal tap-water level. For this animal, use the narrower 18–25°C and pH 6.0–7.5 species ranges while retaining those water-quality limits and weekly monitoring habits.

Make the water decision in the right order

1. Measure the aquarium: test temperature, pH, ammonia, nitrite and nitrate, and establish the general hardness where it is not already known.
2. Compare the residents: find a shared point within 18–25°C, pH 6.0–7.5 and 2–15 dGH that also suits every proposed tank mate.
3. Choose a stable point: maintain one suitable part of the shared range rather than using the full range as a daily operating span.
4. Check trends: compare weekly results with the aquarium’s normal readings so a developing change is noticed early.

Our aquarium water chemistry guide explains what the principal measurements mean. Enter measured values into the water matcher when comparing this range with a planned aquarium.

Temperature decisions should be based on aquarium water rather than an assumption about the room. Seriously Fish estimates roughly 50 W of heating for an 81-litre setup when the room is around 20°C, but heater demand changes with the aquarium and its surroundings. The keeper’s task is to hold the water steadily inside 18–25°C.

Treat replacement tap water with a suitable conditioner to remove chlorine or chloramine before it enters the aquarium. Regular measurement, stable operation and a mature biological filter protect the fish more reliably than reacting to a single reading in isolation.

Feed small food once a day

Rosy Danios are likely to prey chiefly on insects and their larvae in nature. In an aquarium they accept most foods, so use one or two good-quality dried products as the staple and add regular meals of suitably small live or frozen food. Seriously Fish names bloodworm, Daphnia and Artemia as suitable examples for colour and condition.

Follow OATA’s danio schedule by feeding once a day and offering only what the group can eat within a few minutes. This gives a clear observation period: remain at the aquarium, watch food enter the swimming zone and confirm that every fish participates. Food added is not the same as food eaten by each individual.

Build a simple feeding routine

Match particle size to the fish being fed, particularly when caring for one of the smaller dispatch sizes. A piece that remains too large to swallow does not become useful simply because it stays in the aquarium. Use small portions distributed where the group can reach them, then judge the next feed from appetite, body condition and uneaten food.

Overfeeding adds waste that decomposes and can contribute to toxic water conditions. If food remains after the normal feeding period, reduce the next portion and check ammonia, nitrite and the nitrate trend. Do not compensate for one fish missing food by repeatedly adding food to the whole aquarium; first observe whether activity, competition or a health change is preventing that fish from feeding.

A community aquarium adds another decision. Watch the Rosy Danios rather than assuming a general community ration reaches them. Tank mates with a different feeding pace may consume food first, so the combination works only when every resident can obtain an appropriate share without excessive waste.

Introduce the fish to a ready aquarium

Prepare the aquarium before the Rosy Danios arrive. Confirm that its base is at least 90 × 30 cm, the cover closes every escape gap, the filter is mature and the chosen water point lies inside 18–25°C, pH 6.0–7.5 and 2–15 dGH. Ammonia and nitrite must both read zero before fish are introduced.

Follow the arrival steps in order

1. Receive the parcel in person: live fish must not be left unattended. Start filming before opening it, showing the sealed parcel and outer box.
2. Open it continuously on camera: keep filming in one take and show the fish still inside the sealed bag before anything is disturbed.
3. Inspect the fish in the bag: keep the recording running so their condition is visible before acclimatisation begins.
4. Float the bag: float the bag for 20–30 minutes before releasing the fish.
5. Release the fish: never pour the bag water into the aquarium.

OATA advises increasing aquarium stocking slowly because the beneficial bacteria in the filter must adjust when fish waste and feeding increase. Do not add further livestock while the biological filter is adjusting to this group.

Use a first-week observation plan

Healthy fish should show clear, bright eyes, intact scales and undamaged fins, without ulceration or abnormal growths. Learn how the new group normally moves and feeds so that a fish hanging at the surface, sitting on the bottom, swimming erratically or hiding more than usual stands out as a change.

The first feed is an assessment, not a reason for a large ration. Offer food that the selected size can swallow. Reduced appetite may accompany a wider problem, so pair feeding observations with water tests and a check of breathing, colour, fins and body condition.

A successful introduction means stable readings, normal breathing, intact bodies and consistent access to food across the first week. Delay further stocking until the aquarium continues to hold ammonia and nitrite at zero under the new routine.

Keep a weekly maintenance rhythm

Carry out a 25% partial water change at least once every week. In an aquarium holding about 81 litres, 25% is approximately 20 litres. The working volume will be lower where substrate and decor displace water, so use the calculation as a practical starting point and keep the routine consistent.

Use a siphon to remove solid waste from the gravel or sand while taking out the old water. Treat replacement tap water with conditioner before adding it so chlorine or chloramine does not harm the fish or the beneficial bacteria supporting the biological filter.

Combine cleaning with measurement

• Test weekly: ammonia and nitrite should remain at zero, while nitrate should stay no more than 20 mg per litre above the normal tap-water level.
• Compare temperature and pH: look for movement away from the aquarium’s chosen stable point within the species range.
• Inspect the filter: check the intake, outlet and media chamber for blockages.
• Clean media carefully: rinse it lightly in water removed from the aquarium rather than under the tap.
• Review the fish: compare appetite, swimming, breathing, colour, fins, scales and body condition with their normal appearance.

Tap water may contain chlorine or chloramine that can damage the beneficial bacterial population. Cleaning filter media in removed aquarium water reduces that risk. The goal is to clear obstructing debris without stripping away the biological process that converts ammonia and nitrite.

During the first month, keep the weekly results together so trends are visible. A single acceptable reading should not replace the next scheduled test. Repeated zero ammonia and nitrite readings, a controlled nitrate trend and steady fish behaviour show that the aquarium is coping with the group’s waste and feeding.

Use maintenance to inspect escape points as well. Lids and cable gaps can shift during feeding, water changes and filter cleaning. Close them before leaving the aquarium, then confirm that circulation has restarted and the outlet still creates useful movement without torrent-like flow.

If a result differs from the aquarium’s usual pattern, pause further stocking and identify the cause. Water changes, filter checks and reduced excess feeding address husbandry problems directly; do not use medicine as a substitute for correcting the environment.

Respond to health changes with measurements

Observe each Rosy Danio for changes in swimming, colour, temperament, breathing, appearance, body condition and feeding. OATA identifies warning signs including hanging at the surface, sitting on the bottom, erratic swimming, unusual hiding, faster or slower gill movement, white spots, fluffy growths, damaged fins or scales, ulcers, weight change and reduced interest in food.

Start with measurements whenever behaviour or appearance changes. Test temperature, ammonia, nitrite, nitrate and pH, then note recent additions, maintenance, feeding, appetite and which animals are affected. Similar outward signs can accompany different problems, so one symptom should not trigger a guessed treatment.

Match the response to the observation

If ammonia or nitrite is above zero, treat the reading as a water-quality problem and pause further stocking. Check filter operation and blockages, review recent feeding and additions, and carry out the appropriate maintenance without rinsing filter media under the tap.

When one fish stops eating, watch whether it approaches food and whether other residents prevent access. Compare its breathing, colour, fins, scales and body condition with the rest of the group. Avoid adding repeated extra portions because uneaten food creates more waste without solving the cause.

If signs persist or worsen, test the water again and contact us for further guidance. Keep the latest readings, the timing of recent additions or maintenance and a clear description of the changes ready so the next decision can be based on the aquarium’s actual conditions.

Continue daily observation after the immediate problem appears to settle. Restored appetite, normal breathing and stable swimming should accompany zero ammonia and nitrite; an equipment display or clear-looking water should not replace those checks.

Screen every community combination

Rosy Danios are very peaceful fish and can suit a well-furnished community aquarium. Seriously Fish names other small cyprinids, tetras, livebearers, rainbowfish, anabantoids, catfish and loaches as possible community groups. Treat those categories as starting points for assessment, not automatic approval for every species within them.

Check each proposed tank mate by adult size, water overlap, activity, feeding pace, behaviour and the space used by the complete adult community. The chosen combination must share a stable point within the Rosy Danio range of 18–25°C, pH 6.0–7.5 and 2–15 dGH. It must also fit the aquarium after the danio group and decor are included.

Apply the compatibility screen in order

OATA warns that constant danio swimming may stress more timid species. Watch the actual residents after introduction rather than relying only on a species label. Increased hiding, reduced feeding, rapid breathing or a fish remaining away from its normal area calls for water tests and a reassessment of the combination.

Do not transfer numbers between superficially similar fish. Apply the Rosy Danio’s own 90 × 30 cm base, 18–25°C range and group of at least 8–10 when planning this community, then screen every other species against its own adult requirements.

Individual behaviour and aquarium layouts vary, so uncertainty remains with any new mixed community. Make the first combination conservative, observe feeding and stress signals, and reassess promptly if the planned match does not work in practice.

Keep enough Rosy Danios together

Keep Rosy Danios in a group of at least 8–10 specimens. Planning ten or more follows the upper end of that minimum range. A single fish, pair or small handful does not meet the species guidance and may leave the fish more nervous.

Larger groups can create a more natural-looking display and help the fish appear less nervous, but “more” is not permission to overcrowd the aquarium. Every additional fish adds waste, feeding demand and competition for swimming room. Increase the group only when the base, filtration and complete adult stocking remain suitable.

Work through a ten-fish example

1. Purchase unit: each selected unit supplies one animal, so set a quantity of ten to create a group of ten.
2. Footprint: begin with at least 90 × 30 cm rather than choosing the aquarium from body length alone.
3. Adult planning: use the 3.8 cm recorded maximum together with the full group and required swimming footprint.
4. Filtration: prepare the biological filter for the whole group before introduction.
5. Community load: add the adult needs of every tank mate instead of treating 81 litres as a universal stocking allowance.

Male Rosy Danios may show their strongest colours while competing for female attention within a decent-sized group. That observation describes social display, not a method for guaranteeing sex. Use the explicit wording of the selected size only when deciding whether a sex is promised.

Watch individuals within the group. The overall shoal can look active while one fish is excluded from food, hides more than usual or breathes differently. Count the fish during feeding, check that each animal approaches food and respond to persistent changes with water tests and a review of the aquarium.

If the group is nervous, reassess group number, cover, flow, water quality and nearby activity together. Dense planting around the margins can offer security, but it should not reduce the open swimming area below what the full group needs. Add further fish only after confirming that the aquarium has sufficient space and biological capacity.

Answer common Rosy Danio questions

How big does the Rosy Danio get?

It reaches a recorded maximum of 3.8 cm standard length according to FishBase. Plan its space around the complete group and a base of at least 90 × 30 cm.

What size aquarium does the Rosy Danio need?

Use a base of at least 90 × 30 cm, equivalent to about 81 litres, with a mature filter, planting, open swimming room and a tightly fitting cover.

How many Rosy Danios should I keep together?

Seriously Fish says to keep at least 8–10 specimens together. Plan ten or more only when the aquarium, filtration and complete adult stocking can support the larger group.

Is the Rosy Danio suitable for beginners?

Seriously Fish describes it as hardy and ideal for beginners, and we rate its care level as easy when the aquarium is mature, filtered, covered and large enough for the full group.

What does the Rosy Danio eat?

Feed a good-quality dried staple once daily and regularly add small live or frozen foods such as Daphnia, bloodworm or Artemia. Offer only what the group eats within a few minutes.

What temperature and pH does it need?

Keep it at 18–25°C, pH 6.0–7.5 and 2–15 dGH; Seriously Fish gives these as its species-level aquarium ranges. Keep ammonia and nitrite at zero.

Is this fish aggressive or likely to nip fins?

It is described as very peaceful. Screen tank mates for shared water needs and activity levels, and watch whether constant danio swimming causes timid residents to hide or feed less.

Which kinds of fish can live with it?

Seriously Fish names other small cyprinids, tetras, livebearers, rainbowfish, anabantoids, catfish and loaches as possible community groups. Each species must share its water range and fit the complete adult aquarium.

How does this fish arrive alive in the UK?

Someone must be present to receive it. Film every delivery continuously from the sealed parcel as it is opened, showing the animal still in the bag; float the bag for 20–30 minutes, then release the fish without pouring the bag water into the aquarium.

Read the supporting references

Scientific identity and husbandry

• FishBase: Danio roseus — identity, family, distribution, habitat and maximum recorded standard length.
• Seriously Fish: Danio roseus — aquarium footprint, water ranges, layout, feeding, schooling and community behaviour.
• OATA: Danios and white cloud mountain minnows — group guidance on water quality, feeding, maintenance, introduction and warning signs.

Welfare and arrival

• RSPCA: Aquarium environment — biological filtration and aquarium waste processing.
• Tropical Fish Co delivery and Live Arrival Guarantee policy — receipt, unboxing-video and acclimatisation procedure.