Eilyos Tetra (Hyphessobrycon eilyos)

An exceptionally rare Brazilian nano tetra with a dark silver body, vivid carmine-red fins, and a natural preference for quiet, vegetation-rich backwaters.

The Eilyos Tetra, Hyphessobrycon eilyos, is a tiny and rarely available South American tetra native to the upper Rio Araguaia basin in Brazil. Reaching only around 2.5–3 cm, it is a true nano tetra and an excellent choice for aquarists interested in unusual Hyphessobrycon species rather than common mass-produced schooling fish.

In life, this species is characterized by a dark grey body with silvery sides and distinctive red pigmentation in the dorsal, adipose, and caudal fins. Unlike many familiar Hyphessobrycon tetras, it lacks the obvious humeral and caudal spots commonly seen in related species.

Eilyos Tetras originate from calm backwater habitats associated with heavy vegetation and organic material. They are therefore best displayed in a mature, peaceful aquarium with soft water, plants, subdued areas, leaf litter, wood, and a proper group of their own kind.

Why this fish stands out

• Extremely rare Hyphessobrycon species in the aquarium trade
• Native to the upper Rio Araguaia basin in Brazil
• Very small adult size of approximately 2.5–3 cm
• Dark grey to silver body with striking carmine-red fins
• No prominent humeral or caudal spot
• Excellent collector tetra for soft-water nano and planted aquariums
• Beautiful in a larger, calm group against dark substrate and natural botanicals

Best for

• Rare tetra collectors
• Nano fish enthusiasts
• Soft-water planted aquariums
• Botanical and blackwater-style aquariums
• Peaceful South American community tanks
• Aquarists looking for rare tetras in Canada

Origin & Natural Habitat

Hyphessobrycon eilyos was formally described in 2003 from the upper Rio Araguaia basin in Mato Grosso, Brazil. The species is known from tributaries including Ribeirão do Sapo and Córrego do Rancho.

At the type locality, researchers found Eilyos Tetras specifically in quiet backwaters rather than the clear-flowing main channel. These backwaters were tea-coloured and heavily filled with plant debris from the surrounding riparian forest.

This natural history gives us a useful clue for aquarium care: Eilyos Tetras do not need a high-flow river aquarium. A calm, mature aquarium with plant cover, wood, leaf litter, shaded areas, and gentle filtration better reflects the environments in which the species was originally collected.

Topick Aquarium Insight

Rare does not automatically mean difficult, but Eilyos Tetra is not a fish we would treat like a basic beginner Neon Tetra.

Its very small adult size means it can be easily intimidated or outcompeted by larger and faster community fish. A quiet aquarium, appropriately small foods, stable water, and a proper group are more important than simply placing it into a small tank.

The best display is a larger group over a dark background. Their silver-dark body and red fins are subtle individually, but a settled school creates a completely different visual effect than one or two stressed specimens.

What Does an Eilyos Tetra Look Like?

The original scientific description records a dark grey base colour with silvery sides. In living fish, the dorsal, adipose, and caudal fins show striking carmine-red pigmentation.

One useful identification feature is what the fish does not have: Hyphessobrycon eilyos lacks the strong humeral and caudal spots found in many other small Hyphessobrycon species.

Numerous dark pigment cells are concentrated along the body, particularly toward the lower rear portion of the fish, creating a dark, understated appearance that contrasts with the red fins.

Behavior & Recommended Group Size

Eilyos Tetras are peaceful small schooling fish and should not be kept individually.

We recommend at least 8–10 fish, with 10–15 or more preferred when aquarium size allows. A larger group improves confidence, reduces stress, and creates a much more natural display.

They are most suitable for calm aquariums where they do not need to compete constantly with large, aggressive, or extremely fast feeders.

Tank Setup

A mature planted or botanical-style aquarium is ideal. Because this is such a small species, environmental security is more important than large open swimming areas.

• 10 gallons can work for a carefully maintained small group
• 15–20 gallons or larger preferred for a more stable display group
• Dense planting around the sides and background
• Dark substrate helps highlight natural colour
• Driftwood and leaf litter work especially well
• Floating plants can provide shaded areas
• Gentle to moderate filtration preferred
• A mature, biologically stable aquarium strongly recommended

Strong current is unnecessary. Their documented natural habitat includes calm, vegetation-filled backwaters rather than exclusively fast-moving stream channels.

Water Parameters

• Scientific Name: Hyphessobrycon eilyos
• Common Name: Eilyos Tetra
• Origin: Upper Rio Araguaia basin, Brazil
• Adult Size: approximately 2.5–3 cm
• Temperature: approximately 23–27°C
• pH: approximately 5.5–7.0
• Hardness: soft to moderately soft water preferred
• Temperament: Peaceful and social
• Diet: Omnivore / micro-feeder
• Care Level: Intermediate

Stable water is more important than constantly adjusting the aquarium to reach one exact pH value. For recently imported or wild-origin fish, matching softer water and avoiding sudden changes is especially important.

Feeding

Eilyos Tetras have very small mouths and should be offered appropriately sized foods. Large flakes or pellets may simply be too difficult for them to eat efficiently.

• Fine high-quality nano pellets
• Crushed quality flakes
• Baby brine shrimp
• Cyclops
• Daphnia
• Small frozen foods
• Fine live foods when available

A varied diet containing small live or frozen foods is especially useful for bringing newly settled fish into strong condition and encouraging natural colour.

In community tanks, watch the fish during feeding. Larger and faster species can consume most of the food before these tiny tetras have a chance to eat.

Tank Mates

Choose small, peaceful tank mates that will not intimidate or outcompete this tiny tetra.

• Other peaceful nano tetras
• Small pencilfish
• Boraras and other calm nano rasboras
• Pygmy Corydoras
• Small peaceful Apistogramma in larger structured aquariums
• Peaceful dwarf shrimp in planted setups

Avoid large tetras, active barbs, large rainbowfish, aggressive cichlids, predatory fish, and any species large enough to view an Eilyos Tetra as food.

Shrimp Compatibility

Adult dwarf shrimp can generally coexist with Eilyos Tetras in a mature planted aquarium.

However, this is still a small omnivorous fish. Newly hatched shrimplets are small enough to be eaten opportunistically, so a shrimp-only aquarium remains better when maximum shrimp reproduction is the goal.

Breeding

Detailed aquarium breeding information for Hyphessobrycon eilyos remains limited compared with common commercial tetras.

It should be approached like other small egg-scattering Hyphessobrycon species: conditioned adults can be placed into a separate soft-water breeding aquarium containing fine-leaved plants or spawning material.

Adults should not be expected to provide parental care and may consume eggs or newly hatched fry. Very small first foods are required once fry become free swimming.

Conservation & Responsible Keeping

Hyphessobrycon eilyos has a relatively restricted known natural distribution in Brazil and is currently assessed as Near Threatened.

For rare species such as this, responsible long-term maintenance and successful captive breeding are especially valuable. We do not recommend mixing it casually with similar Hyphessobrycon species if maintaining a pure breeding population is the goal.

Canada-Wide Live Fish Shipping

Eilyos Tetra is available from Topick Aquarium in Canada when in stock. Local pickup is available in Markham, Ontario, and Canada-wide live fish shipping may be available depending on weather, route, and livestock condition.

Important Note

Eilyos Tetra is a genuinely small species. Do not confuse its tiny adult size with a lack of care requirements. Stable water, suitable food size, peaceful tank mates, and a proper group are important for long-term success.

Colour may appear muted immediately after transport. The dark silver body and red fin pigmentation generally look much stronger once fish are settled, feeding well, and kept against suitable aquarium backgrounds.

FAQ

What is an Eilyos Tetra?
Eilyos Tetra is a rare Brazilian nano tetra with the scientific name Hyphessobrycon eilyos. It comes from the upper Rio Araguaia basin and reaches only around 2.5–3 cm.

What is the scientific name of Eilyos Tetra?
The valid scientific name is Hyphessobrycon eilyos Lima & Moreira, 2003.

Is Eilyos Tetra rare?
Yes. It remains uncommon in the aquarium trade compared with mainstream Hyphessobrycon tetras and is usually offered only by specialist fish stores or importers.

How big does Eilyos Tetra get?
The species reaches only about 2.5 cm standard length, making it a true nano tetra.

What colour is Eilyos Tetra?
Living fish have a dark grey to silvery body with distinctive red pigmentation in the dorsal, adipose, and caudal fins.

Does Eilyos Tetra need blackwater?
A full blackwater aquarium is not mandatory, but its natural habitat includes tea-coloured backwaters filled with vegetation and organic debris. Soft water, botanicals, plants, subdued areas, and gentle filtration suit the species very well.

How many Eilyos Tetras should I keep?
We recommend at least 8–10, with 10–15 or more preferred when aquarium size allows. Larger groups are more confident and show more natural behavior.

Can Eilyos Tetra live in a 10 gallon aquarium?
A mature 10 gallon aquarium can work for a carefully maintained small group, but 15–20 gallons or larger provides better stability and more room for a proper school.

Can Eilyos Tetras live with shrimp?
Adult dwarf shrimp are generally compatible, but newborn shrimplets can still be eaten opportunistically by small tetras.

What should I feed Eilyos Tetras?
Feed very small foods such as nano pellets, crushed flakes, cyclops, daphnia, and baby brine shrimp. Food size is especially important because this species has a very small mouth.

Is Eilyos Tetra beginner-friendly?
It is better suited to intermediate aquarists. Its rarity, small size, preference for stable soft water, and need for appropriately sized foods make it less forgiving than many common beginner tetras.

Where does Eilyos Tetra come from?
It is native to the upper Rio Araguaia basin in Mato Grosso, Brazil, where it has been documented in quiet, vegetation-rich backwaters.