Characins

“Characin” is a catch-all label people often meet while researching tetras (and their relatives) for an aquarium: what they are, where they come from, what water they prefer, and whether they’ll behave in a community tank. Small differences in temperature, pH, schooling needs and diet can decide whether a tank settles into a steady, quiet rhythm—or slowly unravels into stress, disease, and losses.

Characins are mostly freshwater fishes from the Americas and Africa. Many are small, quick-moving shoalers (the familiar tetras), but the group also includes larger predators such as piranhas. The notes below focus on typical characin care in home aquariums, with reminders to check the needs of your exact species.

Quick profile (typical small aquarium characins)

• Adult size: commonly 2–6 cm for many tetras; some characins grow far larger depending on species^{1, 2}
• Body shape: usually slender to deep-bodied; many species show a small adipose fin (a soft fin between the dorsal fin and tail)¹
• Temperament: many are peaceful shoalers; some are fin-nippers or predators (species-dependent)¹
• Water temperature: often ~20–26 °C for classic small tetras (species-dependent)⁴
• pH: commonly acidic to neutral (often around pH 5.0–7.0 for many Amazonian tetras)⁴
• Diet: varied—many eat small invertebrates and plant material; most do well on quality prepared foods plus small live/frozen options^{1, 4}
• Lifespan: often a few years in captivity when kept in stable conditions (species-dependent)

Important: the original “cat’s nose runs when you pat her” claim is unrelated to characins and has been removed. Characins are fishes; they don’t explain feline nasal discharge.

What “characin” means (and what it doesn’t)

In everyday aquarium talk, “characin” usually refers to small schooling fishes sold as tetras, pencilfish, hatchetfish and similar. In scientific terms, people may be pointing to the family Characidae (a major “characin” family) or, more broadly, the order Characiformes, which includes multiple related families.^{1, 2}

What matters for a home tank is less the label and more the species: some characins stay thumb-sized and drift through plants in a tight school; others are built for open-water pursuit and can swallow tankmates.

Natural range and habitat

Characiform fishes are native mainly to fresh waters of Central and South America and Africa. They are not naturally native to Australian inland waters (though Australia has its own native freshwater fishes from different groups).^{1, 2}

Across that wide range, habitats vary—from tannin-stained “blackwater” creeks under rainforest canopy to clearer tributaries, floodplains and larger rivers. Many small aquarium tetras come from slow-moving, plant- and root-filled streams where cover is constant and light is dappled.^{3, 4}

Behaviour in the aquarium

Many popular characins are shoaling fishes. Kept singly or in very small numbers, they often become withdrawn, pale, and more vulnerable to bullying. In a proper group, they tend to move as a loose, coordinated band—turning together, pausing together, then slipping back into cover when startled.

• Keep a school: aim for at least 6, and often more for small tetras, provided the tank size and filtration can support them.⁵
• Watch for nipping: some species nip fins when cramped, underfed, or kept in poor group sizes.
• Match tankmates carefully: avoid large predatory fish that see small characins as food.

Water conditions: stability beats “perfect numbers”

For many small Amazonian characins (including neon tetras), soft water and an acidic-to-neutral pH is a familiar baseline. Temperature is typically in the low-to-mid 20s °C, with steady conditions more important than chasing an exact set point.^{4, 5}

A few practical notes that tend to help most small characins:

• Gentle flow, high oxygen: many do best with a filter that keeps water clean without blasting them across the tank.
• Dimmer light and cover: plants, driftwood, and leaf litter (where appropriate) create shade and reduce startle stress.
• Clean, consistent water: ammonia and nitrite should be zero; nitrate kept modest with routine maintenance.

Diet and feeding

Wild diets are often built around tiny prey: insect larvae, small crustaceans and other invertebrates, plus varying amounts of plant material depending on species. In the aquarium, most small characins thrive on a quality staple (fine flakes or micro-pellets) with regular additions of frozen or live foods such as brine shrimp or daphnia.^{1, 4}

Feed small amounts and watch the group: the calm ones can be outcompeted by faster tankmates, especially at the surface.

Breeding and life cycle (general pattern)

Many small characins are egg-scatterers, releasing eggs among fine-leaved plants or spawning mops. Adults of some species may eat eggs and fry, so successful breeding often uses a separate breeding setup, gentle filtration, and very small first foods for the fry.

Timelines vary widely by species, temperature and diet, so treat any “one-size-fits-all” maturity or lifespan claim with caution.

Common aquarium examples

Neon tetra (Paracheirodon innesi)

A classic small characin from blackwater or clearwater tributaries of the Amazon system. In aquariums, it’s commonly kept at about 20–26 °C and pH 5.0–7.0, with a preference for stable, softer water and a planted tank with shade.⁴

Conservation and responsible keeping

Some characin species are common in the trade; others have limited ranges and face local pressures such as habitat loss and water quality decline. When possible, choose captive-bred fish from reputable sources and avoid impulse purchases of species that outgrow typical home tanks.

If you keep fish in Australia, be cautious with import rules and biosecurity. Live fish imports are regulated, and only permitted species can be imported under Australian requirements.⁶

References

1. Encyclopaedia Britannica — “Characin” (overview, traits such as toothed jaws and often an adipose fin; range and diversity)
2. Encyclopaedia Britannica — “Characiformes” (distribution in the Americas and Africa; basic classification)
3. Encyclopedia.com — “Characiformes (Characins)” (distribution and broad habitat notes)
4. FishBase — Paracheirodon innesi (neon tetra) summary (pH range, temperature range, distribution notes)
5. Aquariadise — Neon tetra care sheet (schooling guidance and general husbandry notes)
6. Australian Government Department of Agriculture, Fisheries and Forestry — Importing live fish to Australia (ornamental fish import conditions and permits)

Sophie Kininmonth

Veterinary Advisor, Veterinarian London Area, United Kingdom