The Costae Blackline Tetra is a peaceful South American schooling tetra known for its slim silver body and bold black horizontal stripe. It is an elegant community fish valued for its calm temperament and attractive group swimming behavior.

Overview

• Scientific name: Hemigrammus costae

• Common names: Costae Blackline Tetra, Costello Tetra, Blackline Tetra

• Family: Characidae

• Origin: South America

• Adult size: 4–5 cm (1.5–2 inches)

• Lifespan: Around 4–6 years

This species is especially popular in:

• planted aquariums

• blackwater setups

• peaceful community tanks

Appearance

Main characteristics:

• slender streamlined body

• silver-transparent coloration

• dark horizontal black stripe

• reflective scales

The black stripe usually runs:

• from behind the gill plate

• across the body

• toward the tail fin

Other features may include:

• translucent fins

• subtle golden sheen

• faint iridescence under lighting

High-quality specimens usually display:

• clear uninterrupted stripe

• slim balanced body shape

• active schooling behavior

• clean finnage

Their appearance becomes most striking in large groups.

Natural habitat

In the wild, Costae Blackline Tetras inhabit:

• calm tributaries

• forest streams

• slow-moving rivers

• vegetated margins

Natural habitat conditions include:

• soft acidic water

• leaf litter

• submerged branches

• shaded environments

Temperament

Costae Blackline Tetras are:

• peaceful

• active

• social

• schooling fish

They should always be kept in groups.

Recommended:

• at least 8–10 fish

Larger schools improve:

• confidence

• coloration

• natural swimming behavior

They are excellent for peaceful community aquariums.

Aquarium setup

Minimum tank size

• Around 75 liters (20 gallons)

Ideal setup

• planted aquarium

• dark substrate

• driftwood

• open swimming space

• subdued lighting

They look especially attractive in:

• blackwater aquariums

• nature-style planted tanks

Floating plants help reduce stress.

Water parameters

Recommended conditions:

• Temperature: 23–28°C

• pH: 5.5–7.2

• Soft to moderately soft water

• Ammonia/Nitrite: 0

• Low nitrate levels

Stable clean water is important for:

• health

• coloration

• schooling behavior

Diet

Costae Blackline Tetras are omnivores.

Common foods:

• quality flakes

• micro pellets

• frozen daphnia

• baby brine shrimp

• cyclops

• tiny live foods

A varied diet improves:

• activity

• immune health

• coloration

They mainly feed in the mid-water area.

Compatibility

Suitable tankmates:

• rasboras

• peaceful tetras

• corydoras

• pencilfish

• dwarf cichlids

• peaceful shrimp

Avoid:

• aggressive fish

• fin nippers

• large predatory species

They thrive in calm community tanks.

Breeding

Breeding is possible but moderately difficult.

Breeding behavior:

1. Pair or group spawning

2. Egg scattering among plants

3. No parental care

Breeding setup:

• dim lighting

• soft acidic water

• fine-leaf plants or spawning mops

Eggs usually hatch within:

• 24–36 hours

Fry foods:

• infusoria

• powdered fry foods

• baby brine shrimp later

Adults may eat eggs and fry.

Common health problems

Stress fading

Can occur due to:

• small group size

• bright lighting

• poor water quality

Ich

Symptoms:

• white spots

• scratching behavior

Fin damage

Possible causes:

• rough tankmates

• poor maintenance

Good water quality greatly reduces disease risk.

Care difficulty

Costae Blackline Tetras are:

• beginner to intermediate-level fish

Main requirements:

• schooling groups

• stable water

• peaceful environment

• varied diet

Once established, they are relatively hardy.

Difference from Black Neon Tetra

Compared to Black Neon Tetra:

• Costae Blackline Tetras have a slimmer and more transparent body

• Black Neon Tetras display a brighter neon stripe above the black band

Both are peaceful schooling species.

Why aquarists value them

Costae Blackline Tetras are admired for:

• elegant minimalist appearance

• synchronized schooling movement

• peaceful temperament

• compatibility with planted aquariums

A large healthy school creates a sleek, calm, and highly natural freshwater display.