Super Blue Emperor Tetra (Inpaichthys kerri)

Super Blue Emperor Tetra: the quick answer

The fish offered here is the Super Blue trade line of Inpaichthys kerri, a small Brazilian tetra also known as the Blue Emperor Tetra, Purple Emperor Tetra, Kerri Tetra or Royal Tetra. It is not the larger Colombian Emperor Tetra, Nematobrycon palmeri. That distinction matters because the two fish have different identities, origins and care profiles despite the shared trade word “emperor”.

Choose this fish for a mature, well-filtered tropical aquarium with clean, oxygen-rich water, open swimming room and planted or wooded refuge. Keep at least six together; eight to ten or more is a better social group where the aquarium can support it. A tank around 80 cm long and roughly 80–100 litres or larger is a sensible long-term starting point for a group, although stocking capacity depends on the aquarium’s footprint, filtration, existing fish and maintenance rather than litres alone.

Each unit ordered is one unsexed fish in the selected size band. Increase the cart quantity to build the group you need. “Super Blue” is a cultivated colour-line name, not a subspecies and not part of the scientific name. Colour intensity varies with age, sex, condition, stress, background and lighting, so a juvenile or newly transported fish may be paler than a settled adult male. Product images are representative of the form; they are not a promise of sex, individual markings or maximum colour on arrival.

What is a Super Blue Emperor Tetra?

Inpaichthys kerri is a distinct South American characin described from Brazil in 1977. Current taxonomic sources accept that name. Some older aquarium material places it in Characidae, while current FishBase and Eschmeyer’s Catalog of Fishes place it in Acestrorhamphidae, subfamily Thayeriinae. Family-level classifications can change as relationships are revised, so the stable and useful customer anchor is the species name Inpaichthys kerri.

“Super Blue” describes a cultivated aquarium line selected for stronger blue colour. It is best treated like a strain or trade form: useful for identifying what a supplier intends to sell, but not a formal zoological rank. It should therefore appear outside the italicised scientific name. Writing Inpaichthys kerri “Super Blue” or “Super Blue Inpaichthys kerri” is clearer than placing Super Blue inside the binomial as if it were a subspecies.

The common names need care. Blue Emperor Tetra, Purple Emperor Tetra, Kerri Tetra and Royal Tetra are all used for I. kerri. The shorter phrase Emperor Tetra commonly points to Nematobrycon palmeri, a different fish from Colombia. The shared word “emperor” does not make them interchangeable: this listing is the smaller Brazilian Inpaichthys kerri, while Nematobrycon palmeri has its own identity and care profile.

A useful visual distinction is that ordinary I. kerri typically has an adipose fin—the small fin between the dorsal and tail—whereas N. palmeri is usually described without one. Domestic lines can complicate visual rules, and photographs alone should not override supplier identity, so this is a guide rather than a guarantee. Body shape, fin structure, provenance and the full set of markings should be considered together.

Appearance, colour and normal variation

Blue Emperor Tetras are small, laterally compressed fish with a forked tail, a compact mouth and a blue to violet sheen. The ordinary form often shows a dark mid-lateral stripe. In the Super Blue line, metallic colour can spread more strongly across the flanks and make the stripe less obvious in some individuals. The exact balance of blue, violet, silver and dark pigment varies from fish to fish.

Lighting changes what the eye and camera record. A dark background, shaded areas and light arriving from above or slightly in front can reveal iridescence that disappears under a flat, bright shop light. Conversely, intense editing or saturated lighting can make a photograph look more uniformly blue than a living fish will look from every angle. Judge the form by anatomy and consistent markings as well as colour.

Sexual differences are reported by aquarium specialists, but they become clearer with maturity. Males are often slimmer and more intensely blue, while females can be deeper-bodied and less strongly coloured. The adipose fin is commonly described as bluish in males and reddish or orange in females. These clues are not a reliable sex guarantee for every juvenile or every domestic line, and this product’s size options do not promise sex.

A newly delivered fish may temporarily look grey, pale or tightly striped. Transport stress, a new social hierarchy and unfamiliar light can all suppress display. Give the group a calm, stable environment and assess colour over time. Strong colour is never a substitute for good body condition: clear eyes, intact fins, steady breathing, controlled swimming and an interest in appropriately sized food are more useful welfare signs.

Natural range and what it means in an aquarium

Inpaichthys kerri is native to Brazil, specifically the Aripuanã River drainage of the upper Madeira basin in Mato Grosso. It should not be described as a Colombian species; that error belongs to confusion with Nematobrycon palmeri. The original type material came from small streams in the upper Aripuanã region, and later surveys have continued to associate the species with forest-stream habitats in that basin.

Primary field research adds an important correction to the simplified claim that Blue Emperor Tetras are only still-water or blackwater fish. In sampled Aripuanã headwaters, I. kerri was more abundant in faster water with forested margins and well-oxygenated conditions. Recorded dissolved oxygen was roughly 7–9 mg/L at the studied sites. That does not mean a home aquarium needs a torrent, but it supports effective biological filtration, good gas exchange, clean water and some purposeful circulation.

The same field study found an insect-oriented diet that included aquatic and terrestrial insects taken from the drift, with smaller contributions from algae and detritus. In aquarium terms, this supports feeding small foods that move through the water column rather than expecting the fish to graze surfaces or live on leftovers. It also explains why a varied fine dry food supplemented with small invertebrate foods is more convincing than a single-food claim.

Natural-habitat evidence should guide function, not turn the aquarium into a theatrical copy. Forested margins suggest shade and cover; flowing, oxygenated water suggests circulation and gas exchange; small-stream habitat suggests usable swimming length and visual structure. A planted display with wood and open lanes can meet those needs even if it is not a strict biotope. Tannins and botanicals are optional, not mandatory, and any material added to the aquarium should be aquarium-safe.

Adult size and why measurement type matters

FishBase records a maximum of 2.8 cm standard length for I. kerri, and the original description used specimens around that scale. Standard length ends at the base of the tail and does not include the caudal fin. Aquarium sources commonly describe the fish as about 3.5–4 cm overall. Those figures are not contradictory when the measurement methods differ.

For customer planning, expect a genuinely small tetra, but do not use small body length as a reason to choose a very small aquarium. A group needs horizontal swimming room, refuge, stable water and enough volume to buffer change. The tank must also accommodate the adult sizes and behaviour of every companion species. A longer footprint is generally more useful to a moving shoal than a tall, narrow vessel with the same stated litres.

The available options describe the approximate fish size supplied, not a guaranteed final adult size. Living fish vary and measurements are practical bands rather than precision engineering. Select the size that suits the existing community, remembering that a much larger tankmate may see a small new tetra as prey even when both species are otherwise described as community fish.

How many should you keep?

Keep at least six Blue Emperor Tetras together. Where the aquarium has the space, filtration and stocking capacity, eight to ten or more is preferable. FishBase gives a baseline of five or more; UK and European specialist sources commonly recommend a larger group. The recommendation here combines that evidence with a conservative welfare margin rather than pretending there is one experimentally proven magic number.

A group provides more than a visual shoal. It allows courtship, display, retreat and social attention to be distributed among conspecifics. Males may display or make short chases. In an undersized group, or in an aquarium with no visual breaks, that attention can be concentrated on one fish. More companions do not fix crowding, so group size and aquarium size must rise together.

Watch the fish rather than relying only on a number. A healthy group should use the aquarium confidently, feed without one individual being continually excluded, and show periods of loose grouping as well as exploration. Persistent hiding, clamped fins, damage, frantic pacing or one fish repeatedly driven away are reasons to review group composition, cover, tankmates, water quality and available space.

Do not buy a single specimen as a decorative accent. If an emergency leaves one fish alone, plan an appropriate group after checking health and quarantine considerations. Do not solve the problem by mixing it with Nematobrycon palmeri and assuming the shared common name makes them the same social group.

Aquarium size and layout

FishBase cites a 60 cm minimum aquarium length, while specialist husbandry sources often advise more room. For a normal long-term group, this page recommends an aquarium around 80 cm long and roughly 80–100 litres or larger. Treat that as qualified planning guidance, not a laboratory-defined boundary. A larger group, busy community, heavy planting or less efficient footprint requires more capacity.

Before purchase, calculate the whole community at adult size. Filtration rating alone does not create swimming space, and a nominal litre figure does not reveal the area occupied by wood, rock, internal filters and dense plants. Leave a clear midwater lane. Create shaded refuge at the back and ends so a chased fish can move out of sight without being trapped in a dead end.

A secure lid is prudent for a small, active tetra aquarium, especially during arrival and maintenance when fish can startle. Keep intakes safe for the size supplied and ensure water movement does not pin small fish against equipment. A sponge pre-filter can make a powerful intake gentler, but it must be maintained so it does not become blocked.

Use a mature filter capable of processing the aquarium’s total waste load. OATA explains that ammonia and nitrite are toxic and should remain at zero in a mature freshwater aquarium. Adding a group increases feeding and waste at once, so test water before arrival and continue checking after stocking. Do not assume a clear-looking aquarium is chemically safe.

Water temperature, pH and hardness

A well-supported temperature range is 24–27°C. FishBase reports pH 6.0–8.0 and hardness 5–12 dH for the species, while specialist aquarium accounts often favour the softer, more acidic-to-neutral part of that range. The safest interpretation is not to chase the outer limits. Choose a stable point compatible with the fish’s source water and tankmates, then avoid abrupt changes.

For many community aquariums, clean, moderately soft water around slightly acidic to neutral is a practical target. If local tap water is much harder or more alkaline, do not change chemistry with unmeasured products. First test pH, general hardness and carbonate hardness, understand how stable the source water is, and seek experienced advice if modification is needed. A stable, appropriate value is normally safer than repeated swings caused by correction.

Temperature also needs stability. Position the aquarium away from direct sun, radiators, cold draughts and repeated vibration. Use a correctly sized heater with a separate thermometer. During warm weather, remember that warmer water carries less dissolved oxygen; surface movement and sensible stocking become especially important.

Ammonia and nitrite should be zero. Nitrate management depends on source water, stocking, feeding, plants and maintenance, but a rising trend is a warning to review the system. Test results are most useful when recorded so gradual change is visible. When one fish looks unwell, check water and temperature before reaching for medication: poor water quality can cause or worsen many non-specific signs.

Make water changes regular and predictable. OATA gives partial changes up to about 25% weekly as a general freshwater starting point while noting that frequency and volume must suit the system. Match replacement water temperature, use conditioner where required, and avoid washing biological filter media under untreated tap water. Sudden, large chemistry changes can be more stressful than the number you intended to correct.

Filtration, flow and oxygen

Provide effective biological filtration and visible surface movement. The field evidence linking I. kerri with faster, well-oxygenated forest streams makes stagnant water a poor design choice. The goal is steady circulation and gas exchange, not a jet that forces the group to fight current continuously.

Arrange the outlet so the tank contains both moving water and calmer refuge. Watch how the smallest selected size swims. If fish are constantly pushed sideways, confined behind wood or unable to feed, diffuse the flow or redirect it. If they gather at the surface, breathe rapidly or avoid a still area, immediately check temperature, oxygenation, water quality and equipment operation.

Do not turn the filter off for long periods. Nitrifying bacteria depend on oxygenated water, and a stopped filter can deteriorate. Clean mechanical debris as needed while preserving biological media. Use discarded aquarium water for gentle media maintenance and never replace all mature media at once unless a product-specific safety issue requires it.

Plants contribute shelter and can use some dissolved nutrients, but they do not replace filtration, testing or water changes. Likewise, an air stone can improve gas exchange but does not detoxify ammonia. Each part of the system has a different job.

Plants, wood, substrate and lighting

A planted or wooded layout suits this fish well. Use groups of plants, branches or other aquarium-safe structure to break lines of sight, then preserve an open front or central swimming lane. The group should be able to move together without weaving through a solid wall of decoration.

Dim to moderate lighting often shows the blue-violet sheen better than an exposed, very bright tank. Floating cover can soften light, but maintain open surface areas for gas exchange and feeding. A dark background can improve visual contrast without changing the fish. Any lighting change should still meet the needs of live plants.

The substrate may be sand or fine gravel appropriate to the wider community. I. kerri is primarily a midwater fish, so substrate choice is more critical for bottom-dwelling companions. Avoid sharp material where frightened fish could injure themselves and secure all hardscape before filling the tank.

Leaves and aquarium-safe botanicals can add cover and tannins, but they are optional. Add them gradually and monitor pH, oxygen and decay. Do not collect unknown wood or leaves from areas exposed to pesticides or pollution. A clean planted community is valid even if it does not reproduce tea-coloured water.

Temperament and community compatibility

Super Blue Emperor Tetras are generally peaceful community fish when kept in a suitable group and environment. “Peaceful” does not mean behaviour-free. Males display, rivals chase briefly and hungry fish compete. The keeper’s task is to provide enough conspecifics, space, visual barriers and feeding access for those normal behaviours to remain low-risk.

Good companions are peaceful fish of similar scale that share the temperature and water chemistry. Small Corydoras, calm rasboras, pencilfish and appropriately sized peaceful tetras can work when each species’ own group and footprint needs are met. Compatibility must be judged at adult size, not by how small fish look at purchase.

Avoid large predators, highly aggressive fish and very boisterous feeders that repeatedly intimidate or starve the group. Be cautious with persistent fin-nippers and with long-finned, slow fish if the aquarium is cramped. The answer is not a universal banned-species list; layout, group size, individual behaviour and feeding strategy all influence the result.

Do not promise safety with fry or tiny shrimplets. A small insect-eating tetra can investigate and consume animals that fit its mouth. Adult dwarf shrimp may coexist in a heavily structured aquarium, but that is not a guarantee for offspring. If breeding shrimp or fish fry is the goal, use a dedicated setup.

Related alternatives on this site include the Gold Blue Emperor Tetra, Colombia Red Fin Tetra, Rosy Phantom Tetra and Orange Flame Tetra. These are separate products, not interchangeable colour options, so compare adult size, water and behaviour before mixing them.

What and how to feed

Feed a varied, small-particle diet. The strongest species-specific field evidence shows an insect-led diet, including aquatic and terrestrial insects, with lower contributions from algae and detritus. In captivity, use a quality fine flake or micropellet as a practical staple and rotate suitably sized frozen or live invertebrate foods such as daphnia, Artemia or mosquito larvae from safe aquarium sources.

Food must fit the mouth of the smallest fish. Crush or select appropriately rather than relying on large flakes to soften. Distribute food across the swimming area so subordinate fish can feed without crossing one dominant male’s display space. A gentle current can carry particles naturally, but do not let all food disappear into the filter.

Offer only what the group consumes promptly and adjust according to body condition, temperature and the complete community. Repeated overfeeding raises the waste load; underfeeding or using particles that are too large leaves smaller fish thin. A rounded but not swollen abdomen after feeding and stable body condition over time are more useful than a rigid universal portion.

Variety does not mean adding every food at once. Rotate foods over the week and store them correctly. Thaw frozen portions as directed and do not introduce wild-caught live food from water that may carry pollutants, parasites or invasive organisms. Remove persistent uneaten food and review portion size.

Colour-enhancing ingredients cannot replace appropriate care. Genetics, maturity, sex, social confidence, lighting and water quality all affect blue display. Be sceptical of any diet promising that every juvenile will become identical to a saturated adult-male photograph.

Arrival and acclimation

Prepare the aquarium before dispatch. Confirm the filter is mature, temperature is stable, ammonia and nitrite are zero, and existing fish are compatible. Check the chosen delivery date and the current Live Arrival Guarantee conditions before ordering, because livestock evidence and contact windows matter if a problem occurs.

These fish are sent using a licensed live-animal courier. On arrival, follow the acclimation instructions supplied with the order and avoid unnecessary delay. OATA’s general freshwater guidance recommends dimming the aquarium lights, equalising temperature and gradually matching water conditions; it describes both floating-bag and drip methods. The correct method can depend on transport time and the chemistry difference, so the retailer’s current livestock instructions take priority over generic internet recipes.

Do not pour transport water into the aquarium unless instructed. Use clean equipment dedicated to aquarium use, keep lids secure and reduce disturbance. A quarantine aquarium is valuable where practical because it allows observation without exposing an established community, but it must itself be mature, heated, covered and appropriately filtered.

Expect colour to be subdued after travel. Monitor breathing, balance, swimming, appetite and interaction rather than trying to force immediate display with bright lights or heavy feeding. Offer a small suitable meal once the fish are settled according to the supplied instructions. Test water more frequently during the first week because adding a group increases the biological load.

Routine welfare and health checks

Observe the group daily. Healthy signs include clear eyes, intact scales and fins, controlled swimming, steady breathing and an appropriate feeding response. Compare each fish with the group: a single animal that hangs apart, loses weight, clamps its fins or breathes faster deserves attention even if the others appear normal.

OATA recommends watching for changes in colour, temperament, swimming, breathing, appearance, body condition and feeding. These signs are not a diagnosis. First check temperature, ammonia, nitrite, nitrate trend, pH stability, oxygenation and equipment. If welfare concerns continue, contact an experienced aquatic retailer or fish veterinarian with the test results and clear photographs or video.

Do not medicate the display aquarium “just in case”. Different problems can look similar, and inappropriate treatment may harm fish, invertebrates or filter bacteria. Isolate when advised, calculate water volume accurately and follow product or veterinary directions. Never combine medicines without confirming compatibility.

Preventive care is mostly consistent husbandry: a mature filter, sensible stocking, varied food, appropriate groups, safe maintenance and quarantining additions where possible. Record test results and changes. A log makes it easier to connect a problem with a heater fault, missed maintenance, new livestock or altered feeding.

Breeding: what is known and what is not promised

Inpaichthys kerri is recorded as an egg-scattering fish without parental care. Hobby and specialist accounts describe spawning among fine plants or mops in soft, acidic water, with adults liable to eat eggs. That makes a separate mature breeding aquarium and protected spawning medium more plausible than expecting a community tank to raise many young.

Detailed claims about exact egg number, hatching time, maturity age and success rate are not well established by strong species-specific studies. They vary with temperature, parent condition and method. This listing therefore does not promise a breeding pair, a sex ratio or a particular outcome.

If breeding is the goal, begin with a healthy group, stable water and a varied diet. Research a dedicated method before spawning and prepare first foods in advance. Do not move adults between very different water chemistry suddenly. Any fry require tiny foods, clean water and safe filtration, and the keeper must have space for the resulting group.

Is this fish right for your aquarium?

This fish is a good choice when you want a small blue-violet midwater group and can provide stable tropical water, oxygenation, a mature filter and appropriate companions. It is not a good choice for an uncycled aquarium, a solitary display, a tiny vessel, a tank of large predators or a system where water chemistry swings repeatedly.

Care is rated moderate rather than automatically easy. The fish is small and usually peaceful, but good outcomes depend on details that “beginner fish” labels often hide: group structure, feeding access, mature filtration, oxygen, stable chemistry and correct identification. A prepared first-time keeper can succeed; an experienced keeper can still have problems if those basics are ignored.

Before ordering, answer five questions: Is the aquarium mature? Is it around 80 cm long or otherwise genuinely suitable for the planned group? Are ammonia and nitrite zero? Do all tankmates share the required water and lack the size or temperament to threaten these fish? Are you ordering at least six, preferably eight to ten where capacity permits? If any answer is no, solve it before arranging livestock delivery.

References and further reading

1. Eschmeyer’s Catalog of Fishes: Inpaichthys kerri — accepted name, classification, type locality and distribution.
2. FishBase: Inpaichthys kerri — size measurement, distribution, water range and aquarium group baseline.
3. Géry and Junk (1977), original description — species identity, type material and locality.
4. Zeni and colleagues (2020), Neotropical Ichthyology — primary evidence on habitat use, oxygen and diet in Aripuanã streams.
5. Ferreira and colleagues (2024), redefinition of Inpaichthys — recent genus-level taxonomy and morphology.
6. GBIF species record — accepted name and recorded vernacular names.
7. AMAZONAS Magazine: Blue Kerri Tetras — specialist context for the cultivated Super Blue line.
8. Fishkeeper: Blue Emperor Tetra — UK specialist husbandry, appearance and feeding guidance.
9. Ornamental Aquatic Trade Association freshwater aquarium guidance — filter maturity, water testing, acclimation and routine welfare checks.

Ordering live fish from Tropical Fish Co

Select the available size and the quantity needed for a proper group. Livestock is packed for delivery using a licensed live-animal courier. Review the current delivery information and Live Arrival Guarantee conditions before choosing the date, then prepare the mature aquarium before dispatch. If you are unsure whether your water, existing stock or aquarium size is suitable, ask before ordering rather than trying to solve a compatibility problem after arrival.