Dwarf Australian Rainbow (Melanotaenia maccullochi)

Decide whether this social rainbowfish fits your aquarium

The Dwarf Australian Rainbow, Melanotaenia maccullochi, is a small freshwater rainbowfish from north-eastern Australia. It is also known as Macculloch’s rainbowfish and belongs to the family Melanotaeniidae. Its peaceful temperament and active social behaviour make it a candidate for planted species aquariums and carefully planned communities rather than solitary display.

FishBase records a maximum of 7 cm standard length for male or unsexed fish. Plan the aquarium around that adult measurement, the space needed by a complete shoal and the swimming activity of the group. A small body does not turn a social fish into a suitable single inhabitant for a small container.

Start with the decisive requirements

The aquarium figures above come from the Seriously Fish species account for Melanotaenia maccullochi. The pH can vary with collection locality, so measure your aquarium and tap water rather than choosing companions from a temperature figure alone.

Check whether the plan fits

This fish suits a keeper who can maintain a mature biological filter, perform weekly partial water changes and reserve enough room for a proper shoal. It is a less suitable choice when the aquarium cannot accommodate six fish, has forceful flow throughout, lacks cover or already contains companions that would be overwhelmed by an active group.

Before choosing this species, compare the adult dimensions, social needs and water requirements of the whole planned community. You can also browse the current rainbowfish collection when deciding whether this smaller species or a different rainbowfish better matches the aquarium.

Choose the dispatch size and quantity separately

One purchase supplies one Dwarf Australian Rainbow in the size selected. The live size selector carries 4.5–5 cm and >6 cm dispatch sizes. Check the selector when choosing the size rather than relying on static text about a particular selection.

The size you select is the size supplied, not the adult size. Dispatch size describes the animal at fulfilment, while the recorded adult maximum is 7 cm standard length. The >6 cm label is open-ended and should not be read as a promise of a particular age, sex or eventual measurement.

Convert the shoal plan into a purchase quantity

Because each purchase supplies one animal, a planned group of six requires a total quantity of six. A planned group of eight requires a total quantity of eight. If you combine dispatch sizes, count every selected animal towards the total group while keeping the aquarium’s space, filtration and existing livestock in view.

• First decision: confirm that the aquarium can support a shoal of at least 6–8.
• Second decision: choose the preferred dispatch size from the live selector.
• Third decision: set the total quantity to the number of animals required.
• Final check: assess the complete adult stocking plan, not only the centimetres shown beside the selection.

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

Do not infer sex or life stage from dispatch size, colour or gallery appearance. Mature males may become more colourful and develop longer dorsal and anal fins than deeper-bodied females, but those mature traits are observational differences rather than a promise about the animal supplied.

These representative gallery images have been digitally enhanced for presentation, so colours can look slightly different from the live animal.

Prepare the aquarium for the full quantity before completing your selection. For timing, coverage and claims procedures, read our current delivery and Live Arrival Guarantee policy.

Shape a planted layout around swimming room

Use an aquarium with a base of at least 60 × 30 cm and a volume of about 54 litres for the species setup described by Seriously Fish. Treat both measurements as part of the decision. A nominal volume in a tall or unusually shaped aquarium does not automatically create the same horizontal layout.

Build heavy planting around open water rather than filling every part of the aquarium with stems or ornaments. This arrangement gives the shoal cover while preserving clear areas for swimming and male display. Keep flow quite slow across those open lanes and position the filter return so the entire aquarium is not dominated by a forceful current.

Divide the footprint into useful zones

Aquarium gravel or sand can form the base. Live plants are the preferred way to supply cover, particularly because this species is ideally suited to a heavily planted setup. If live planting is not used throughout, suitable artificial plants and aquarium ornaments can supply shelter, but they should not consume the swimming area required by the shoal.

Keep the group requirement in view as you place every object. Six to eight active fish need connected swimming space, not several small pockets divided by solid décor. Leave visible routes through the centre and between planted sections, then inspect the layout from both ends to check that dense planting has not created dead ends.

The 54-litre figure is a species aquarium reference, not a promise that every community combination will fit. Existing fish, additional shoals and bottom-dwelling companions all add demands on footprint, filtration and water quality. Increase aquarium size when the complete stocking plan cannot preserve cover and open water at the same time.

Finish the physical layout before adding livestock so plants, equipment and access points can be adjusted without disturbing the group. A stable arrangement also makes later changes in hiding, swimming route or social behaviour easier to notice.

Hold the aquarium inside the species water range

Set aquarium temperature within 20–30°C, pH within 5.5–8.0 and general hardness within 8–15 dGH. The pH range varies with collection locality, so use measured values and consistency when selecting the aquarium and its companions. Do not choose a target only because it sits somewhere inside a broad temperature overlap.

Separate habitat values from waste targets

OATA’s rainbowfish guidance is broad group guidance: it gives ammonia and nitrite at zero mg per litre and nitrate at no more than 20 mg per litre above the normal tap-water level. These waste targets support the high water quality required by Melanotaenia maccullochi.

Measure the aquarium before introducing the shoal, then test at least weekly as part of routine maintenance. Record the result rather than relying on clear-looking water. Ammonia and nitrite are invisible, and a change in fish behaviour may be the first noticeable sign that waste processing has fallen behind.

Use our aquarium water chemistry guide to understand what each measurement means. Once you have actual readings, the water matcher can help compare them with the stated aquarium range.

If ammonia or nitrite is detected, pause further stocking and check the filter, feeding and maintenance routine. When nitrate rises beyond its target, carry out the planned partial water change and review whether waste, feeding or total stocking is increasing faster than the aquarium can manage.

Test the replacement water as well when tap-water conditions vary. The aim is an aquarium that remains inside the chosen part of the species range while biological waste stays controlled, not a series of abrupt reactions to isolated readings.

Size filtration to the aquarium without creating harsh flow

A working biological filter is essential. The RSPCA explains that biological filtration supports beneficial bacteria that convert toxic ammonia to toxic nitrite and then to safer nitrate. That process is why a clean-looking but immature aquarium is not ready for a shoal.

For the species setup of about 54 litres, Seriously Fish uses a turnover of four to five times the aquarium volume per hour and gives a filter rating of roughly 215–270 litres per hour. The calculation is straightforward: 54 litres multiplied by four is about 216 litres per hour, while 54 multiplied by five is 270 litres per hour.

Balance three filter decisions

Filter ratings and experienced flow are not the same decision. A unit can meet its nominal turnover while its outlet creates a concentrated jet. Position or diffuse the return so water continues moving through the filter without forcing the fish to swim continuously against a strong current.

Check the filter for blockages during weekly maintenance. When its media needs cleaning, rinse it lightly in aquarium water removed during the partial water change. Do not rinse mature biological media under the tap because chlorine or chloramine may damage the beneficial bacterial population.

Seriously Fish also gives a heater example of roughly 75–100 W for a 54-litre aquarium when the room is around 20°C. Treat that as a worked example under the stated room condition. Select and set equipment to hold the aquarium inside 20–30°C, then confirm the result with measurement rather than wattage alone.

After any filter cleaning or equipment adjustment, confirm that flow remains slow enough for the planted layout and continue checking ammonia and nitrite. A filter must satisfy both parts of the job: biological waste processing and a current that suits the fish.

Keep a complete shoal rather than a single fish

Keep Melanotaenia maccullochi in a shoal of at least 6–8, preferably more. This species can be skittish and performs much better in a proper social group. Conspecific company also encourages males to display their stronger mature colours.

Six should be treated as the lower edge of the species recommendation, not a target to divide across separate aquariums. If an existing group falls below that threshold, assess aquarium space, filtration and compatibility before increasing it. More fish may improve the social setting, but only when the aquarium can support the resulting total load.

Read group size together with space

Watch how the group uses the aquarium. Coordinated swimming through open areas, regular feeding and normal social display are useful reference behaviours. Repeated hiding, isolation, unusual bottom-sitting or hanging at the surface should prompt an immediate water test and a review of group pressure, current and tank mates.

Mature males may be more colourful and have longer dorsal and anal fins, while mature females may be deeper-bodied. Use those distinctions only when observing mature fish. They do not create a dependable way to select sex from a dispatch measurement or a representative image.

Do not force a preferred male-to-female ratio when the chosen option carries no sex selection. Build the aquarium around the number of animals, their adult size and the group’s social needs. If the sexes later become apparent, continue to watch whether every fish can feed and use cover without persistent pressure.

A complete shoal is one stocking component. Community companions do not replace members of the same species, even when they swim in a similar part of the aquarium. Reserve the first share of space and filtration for the Dwarf Australian Rainbow group before considering additional species.

Feed one measured meal and vary the food type

The Dwarf Australian Rainbow is an omnivore that accepts most dried, frozen and live aquarium foods. Use a good-quality flake or granule as the regular dried food, then include suitable small live or frozen items such as daphnia, small bloodworm or tubifex. Regular live and frozen food can help the fish display their best colours.

Feed once a day and offer only what the group can consume within a few minutes. This limit is more useful than a fixed pinch because the correct amount changes with group size, food form and feeding response. Stop adding food when the fish no longer take it promptly.

Give each part of the diet a clear role

Distribute the meal so the whole shoal has an opportunity to feed. Watch for an individual that repeatedly misses food, withdraws from the group or loses condition. That observation can reveal social pressure, illness or an unsuitable feeding pace before the problem becomes severe.

Do not respond to enthusiastic feeding by extending the meal. Rainbowfish may continue to show interest after an adequate portion, while uneaten food breaks down and releases waste into the water. Overfeeding therefore affects both body condition and the ammonia, nitrite and nitrate load managed by the filter.

At each meal, check that the food form can be taken readily and that leftovers are not settling among plants or into the substrate. Remove visible excess during maintenance and reduce the next portion rather than allowing a repeated accumulation.

Use dietary variety without turning every day into several separate feeds. One measured daily meal remains the schedule, and the food offered within that meal can vary between the dried staple and appropriate live or frozen choices. This keeps the feeding rule simple enough to apply consistently across the whole shoal.

Make testing and water changes a weekly routine

Carry out a partial water change of 25% at least once every week. Use a siphon to remove solid waste from the gravel or sand, and treat replacement tap water with a suitable conditioner to remove harmful chlorine or chloramine before it enters the aquarium.

Test the water at least weekly and compare the results with the targets already set for the aquarium. High water quality is essential for this species, so the change and test should remain scheduled even when the water looks clear and the fish are feeding.

Use one repeatable maintenance sequence

1. Observe swimming, breathing, colour, fins, scales, body condition and feeding response.
2. Test the aquarium water before deciding whether any unusual behaviour is social or environmental.
3. Siphon waste while removing 25% of the aquarium water.
4. Treat replacement tap water before adding it to the aquarium.
5. Check the filter for blockages and inspect the flow through open swimming areas.
6. Clean filter media lightly in removed aquarium water only when cleaning is needed.
7. Record the test results and any behavioural changes for comparison the following week.

Changes worth acting on include hanging at the surface, sitting on the bottom, erratic swimming, a marked change in colour, increased aggression, unusual hiding, faster or slower gill movement, white spots, fluffy growths, damaged fins or scales, weight change and reduced interest in food.

If you see one of these changes, test water quality first and compare the affected fish with the normal behaviour of the rest of the group. Correct any husbandry problem identified and contact us for further guidance on health changes. Do not choose medication from a symptom name alone.

Weekly records help separate a one-off observation from a continuing trend. For example, a rising nitrate result across successive tests points towards a growing waste load, while a change immediately after filter maintenance directs attention to filtration and water conditions.

Keep maintenance proportionate but consistent. A 25% change at least once a week is the stated baseline, while measured water quality, accumulated waste and the condition of the shoal show whether the aquarium needs closer attention.

Introduce the shoal only after the aquarium passes its checks

Prepare and mature the aquarium before the fish arrive. A mature biological filter needs an established bacterial population capable of converting ammonia and nitrite, and both compounds should test at zero mg per litre before livestock is introduced. Our first tropical aquarium guide explains how to prepare the system before livestock.

Before introduction

• Confirm a temperature of 20–30°C, pH of 5.5–8.0 and hardness of 8–15 dGH.
• Test ammonia and nitrite at zero mg per litre.
• Confirm that the filter is working and open swimming areas have quite slow flow.
• Check that planting supplies cover without blocking the 60 × 30 cm footprint.
• Count the planned shoal and all existing livestock in the stocking assessment.

Increase the aquarium population slowly. Every additional fish and every increase in feeding creates more waste, while the beneficial bacteria in the mature filter need to support that increased load. Adding livestock faster than the filter can respond can lead to new tank syndrome and harmful ammonia or nitrite.

During the first week

Use the daily feed as an observation point. Check whether all fish take food, swim with the group and use both cover and open water. Look for clear eyes, intact scales and fins, appropriate swimming and the absence of bumps or ulcerated areas. Test immediately if a fish hangs at the surface, remains on the bottom or becomes erratic.

Through the first month

Continue the same weekly testing and 25% partial water changes at least once a week. Record food intake, group cohesion and any changes in hiding, breathing or colour. Keep further livestock additions on hold until the filter continues to return zero ammonia and zero nitrite with the existing population.

If the shoal remains withdrawn, assess water values, current, cover, group size and the behaviour of companions rather than assuming the fish simply need more time. Each of those factors has a direct care action: correct the water, soften excessive flow, restore cover, complete the social group or reconsider a stressful community combination.

Screen every companion for size, pace and water overlap

Melanotaenia maccullochi is described as very peaceful and suitable for many community aquariums. That does not make any fish an automatic companion. Screen each proposed combination for adult size, temperament, activity, feeding pace, water requirements and the space left after the rainbowfish shoal is counted.

Conditional candidates include similarly sized rainbowfish, characins, danios, barbs, dwarf cichlids, freshwater gobies and Corydoras. These groups are starting points for assessment, not universal matches. Individual species within them can differ in adult size, behaviour and water needs.

Avoid mixing geographical variants of Melanotaenia maccullochi because they may hybridise. Plan a single variant as one complete shoal rather than combining visibly different forms.

Apply the same screen in the same order

Do not treat a shared temperature as a complete match. A fish can overlap at 24°C while falling outside the required hardness, using the same crowded swimming area or feeding too slowly beside an active shoal. All parts of the screen must work together.

Watch the community after introduction. Increased hiding, reduced feeding, isolation or persistent displacement from open water indicates that the practical combination needs reassessment even when both species fit the measured water range.

For a stocking and compatibility assessment, contact us with aquarium dimensions, measured temperature, pH and hardness, filter details, current livestock and the number of Dwarf Australian Rainbows planned. Those details allow a specific assessment without turning a conditional candidate into a blanket recommendation.

Build the whole stocking plan before adding companions

Start the stocking plan with the Dwarf Australian Rainbow shoal rather than fitting it into space left by other fish. Reserve a 60 × 30 cm base, about 54 litres, heavy planting, open swimming room and capacity for at least 6–8 individuals. Only then assess what additional livestock the aquarium can support.

Example one: a species-focused aquarium

For a species-focused plan, begin with the stated 54-litre and 60 × 30 cm setup, then count a complete shoal of at least six. Arrange planting around connected open lanes, set slow flow and size the filter around the whole group. Increasing the shoal beyond the starting band may improve the social setting, but it also increases the demand on space and filtration.

Example two: a proposed community

For a community plan, do not subtract the rainbowfish from a simple litre allowance and assume the remainder can be filled. List every species with its adult size, group requirement, water range, swimming area and feeding pace. Reject a proposed combination if it removes the open water, pushes a companion outside its preferred water or creates more waste than the mature filter can process.

Example three: adding to an established aquarium

Measure the existing aquarium and test its water before selecting a quantity. Confirm that the current temperature, pH and hardness fit the rainbowfish, then observe whether existing fish are timid, substantially smaller or slow at feeding. Review recent ammonia, nitrite and nitrate results rather than assuming past stability will continue after a new shoal is added.

A larger aquarium generally gives more stable environmental conditions, but volume alone does not resolve an unsuitable social or water match. Use extra space to protect group size, cover and swimming room rather than simply increasing the number of species.

Answer the key questions before you choose

How big does the Dwarf Australian Rainbow get?

The Dwarf Australian Rainbow reaches a recorded maximum of 7 cm standard length, so plan its aquarium and complete shoal around that adult figure rather than its dispatch size.

What size aquarium does Melanotaenia maccullochi need?

Plan about 54 litres with a base of at least 60 × 30 cm, heavy planting, connected open swimming areas, slow flow and mature biological filtration.

How many Dwarf Australian Rainbows should I keep together?

Keep a shoal of at least 6–8 Dwarf Australian Rainbows, preferably more, because this social species can be skittish and performs better with its own kind.

Does this fish suit a beginner?

It can suit a beginner who prepares a mature filtered aquarium, keeps the complete shoal, tests water at least weekly and carries out a 25% partial water change at least once a week.

What does it eat?

Feed a quality flake or granule once daily, vary it with suitable small frozen or live foods, and limit the meal to what the shoal eats within a few minutes.

What temperature and pH does the Dwarf Australian Rainbow need?

Keep the Dwarf Australian Rainbow at 20–30°C and pH 5.5–8.0, with general hardness of 8–15 dGH and ammonia and nitrite at zero mg per litre.

Is it aggressive or likely to nip fins?

It is described as very peaceful. Keep a complete shoal and choose peaceful companions whose adult size, activity and feeding pace will not place persistent pressure on the group.

Which kinds of animals can this fish live with?

Conditional candidates include similarly sized rainbowfish, characins, danios, barbs, dwarf cichlids, freshwater gobies and Corydoras when their water, adult size, temperament, feeding pace and space needs align; avoid mixing geographical variants of this species.

How does the Dwarf Australian Rainbow arrive alive in the UK?

Have someone present to receive the parcel. For every delivery, start filming continuously while the parcel is still sealed, then show it being opened and the fish still inside the sealed bag; float the bag for 20–30 minutes before releasing the fish, and never pour the bag water into the aquarium.

Read the principal identity and care references

• FishBase: Melanotaenia maccullochi identity, family, north-eastern Australian distribution and maximum recorded standard length.
• Seriously Fish: Species aquarium dimensions, water range, planted layout, flow, feeding, group behaviour and conditional community guidance.
• Ornamental Aquatic Trade Association: Rainbowfish husbandry, water-quality targets, feeding schedule, introduction, observation and weekly maintenance.
• RSPCA: The role of mature biological filtration in processing ammonia and nitrite in aquariums.
• Tropical Fish Co delivery policy: Receipt, continuous unboxing video and acclimatisation procedure.