Freshwater Fish Care Sheets

Tetras, Pencilfish & Hatchetfish Care Guide

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Quick Facts

  • Difficulty: Beginner for most species; a handful (Cardinal-type morphs, Green Neon Tetra, Gold Rummy Nose Tetra) are Intermediate due to stricter soft/acidic water needs
  • Temperament: Peaceful, shoaling fish for the vast majority; a few species are semi-aggressive fin-nippers when kept in insufficient numbers
  • Diet: Omnivorous micro-predators — high-quality micro pellet/flake plus regular live or frozen foods (brine shrimp, daphnia, bloodworm, micro worms)
  • Min Tank Size: 45–60cm (34–60L) for nano/small species (Ember Tetra, Neon Tetra, pencilfish); 90–120cm+ for larger, more active or surface-swimming species (Congo Tetra, hatchetfish, Bleeding Heart Tetra)
  • Water Type/Parameters: Soft to neutral, slightly acidic to neutral water (pH ~5.0–7.5); temperature 22–28°C, with true Amazon blackwater species (Cardinal Tetra, Rummy Nose Tetra, pencilfish) preferring the warmer, softer, more acidic end
  • Typical Size: 2cm (Ember Tetra) up to 8–10cm (Blind Cave Tetra, Congo Tetra, Bleeding Heart Tetra)
  • Origin: Predominantly South America (Amazon, Orinoco, Paraguay and coastal Guiana basins); Congo Tetra is African (Congo River basin); Blind Cave Tetra is Central American/Mexican
  • Lifespan: Typically 3–5 years in well-maintained aquaria; some (Buenos Aires Tetra, Congo Tetra) can reach 5–8 years

Overview & Natural Origin/Habitat

Tetras, pencilfish and hatchetfish all belong to the order Characiformes (the "characins"), one of the largest and most diverse groups of freshwater aquarium fish. The overwhelming majority stocked in this range originate from the river systems of tropical South America — the Amazon, Rio Negro, Orinoco and Paraguay basins — with a smaller number from Central America (Blind Cave Tetra) and Africa (Congo Tetra, from the Congo River basin). In the wild, many of the most popular species (Cardinal Tetra, Neon Tetra, Rummy Nose Tetra, pencilfish, hatchetfish) are true "blackwater" fish, living in tannin-stained, nutrient-poor forest streams with very soft, acidic water and dense overhanging vegetation. Others (Buenos Aires Tetra, Bloodfin Tetra, Black Widow Tetra) come from more open, whitewater or clearwater rivers further south and tolerate harder, cooler or more neutral water. Hatchetfish and many pencilfish are specifically adapted to life at the water's surface in slow, still, densely vegetated backwaters.

Appearance & Size

Characins are small, laterally compressed, streamlined fish, almost all schooling species with an adipose fin — a hallmark of the group. Colouration ranges from the iridescent neon-blue-and-red stripe of the Cardinal and Neon Tetras, through the metallic sheen of Diamond and Congo Tetras, to the more understated silver bodies of Bloodfin and Head-and-Tail Tetras. Pencilfish (Nannostomus) are named for their slender, torpedo-like, horizontally striped bodies and swim in a distinctive head-up posture. Hatchetfish (Gasteropelecus) have a unique, deeply keeled belly housing enlarged pectoral muscles that let them "fly" short distances above the water surface to escape predators. Most species top out between 2cm (Ember Tetra) and 8cm, with a few outliers reaching 8–10cm (Blind Cave Tetra, Bleeding Heart Tetra, Congo Tetra males).

Species Commonly Stocked

  • Neon Tetra (Paracheirodon innesi) — to ~3–4cm. The classic beginner tetra; unusually cool-tolerant (21–25°C).
  • Green Neon Tetra (Paracheirodon simulans) — to ~3–4cm. Smaller, more delicate; needs stable, soft, acidic water.
  • Cardinal Tetra (Paracheirodon axelrodi) — to ~5cm. Full-length red stripe; prefers warmer, softer, more acidic water than Neon Tetra.
  • Black Neon Tetra (Hyphessobrycon herbertaxelrodi) — to ~3–4cm. Hardy, black-and-white horizontal stripe.
  • Serpae Tetra (Hyphessobrycon eques) — to ~4cm. Deep red body; the best-known fin-nipper in the tetra world — keep only in large groups (12+) with fast, robust, short-finned tankmates.
  • Phantom Tetras (black, red, yellow — Hyphessobrycon megalopterus/sweglesi/roseus) — to ~3–4cm. Males spar/flare at each other but rarely cause real injury.
  • Rosy Tetra (Hyphessobrycon rosaceus) — to ~5cm. Soft pink body, black-tipped fins.
  • Flame (Rio) Tetra (Hyphessobrycon flammeus) — to ~3–4cm. Very hardy, tolerant of a wide parameter range.
  • Lemon Tetra (Hyphessobrycon pulchripinnis) — to ~5cm. Pale yellow with black-edged anal fin.
  • Bleeding Heart Tetra (Hyphessobrycon erythrostigma) — to ~7–8cm, the largest true Hyphessobrycon here; needs a larger tank than most tetras.
  • Emperor Tetra (Nematobrycon palmeri) — to ~4–5cm. Hardy, long-lived, less strictly schooling than most tetras.
  • Royal/Blue Emperor Tetra (Inpaichthys kerri) — to ~3–4cm. A distinct species despite the overlapping common name; iridescent purple-blue, peaceful.
  • Black Widow (Black Skirt) Tetra (Gymnocorymbus ternetzi) — to ~5–6cm. Very hardy and adaptable; colour fades to grey with age.
  • Diamond Tetra (Moenkhausia pittieri) — to ~5–6cm. Sparkling scale sheen; larger and calmer than many tetras.
  • Red Eye Tetra (Moenkhausia sanctaefilomenae) — to ~7cm. Active, hardy, adaptable, occasionally nippy if kept alone.
  • Glowlight Tetra (Hemigrammus erythrozonus) — to ~4–5cm. Iridescent orange-red stripe; easy, peaceful blackwater species.
  • Head and Tail Light Tetra (Hemigrammus ocellifer) — to ~4–5cm. Reflective gold eye-spot and tail-spot; easy and undemanding.
  • Rummy Nose Tetra (Hemigrammus bleheri) — to ~5cm. Bright red nose — a prized "living water-quality indicator" whose colour fades under poor conditions; needs stable, pristine, warm, soft water and tight schooling numbers (8+).
  • Silver Tip Tetra (Hasemania nana) — to ~3–4cm. Golden-bronze body with white-tipped fins.
  • Pristella Tetra (Pristella maxillaris) — to ~4–5cm. Translucent body; one of the most tolerant and adaptable tetras.
  • Buenos Aires Tetra (Psalidodon anisitsi) — to ~7–7.5cm. Large, hardy, unusually cold-tolerant; a robust feeder that can nip fins if underfed — best in 6+ and fed generously.
  • Bloodfin Tetras (Aphyocharax anisitsi, A. rathbuni) — to ~5cm. Translucent silver body with red fins; strong jumpers, tolerate cooler water than most tetras.
  • Blue King Tetra (Boehlkea fredcochui) — to ~5cm. Electric-blue schooling tetra; can nip and is best kept in a large group.
  • Penguin Tetra (Thayeria boehlkei) — to ~5–6cm. Distinctive head-up swimming angle and black diagonal tail stripe.
  • Ember Tetra (Hyphessobrycon amandae) — to ~2cm, the smallest species in this range; ideal for nano and planted tanks, best in groups of 10+.
  • Congo Tetra (Phenacogrammus interruptus) — to ~8cm. African species; needs a longer tank (120cm+) than most tetras, more sensitive to poor water quality, and its flowing fins are vulnerable to fin-nippers.
  • Blind Cave Tetra (Astyanax mexicanus) — to ~8–10cm. Cave-adapted, eyeless population of the Mexican tetra; navigates by lateral-line sensing; extremely hardy.
  • Splashing (Splash) Tetra (Copella arnoldi) — to ~5–7cm. Leaps clear of the water to lay eggs on leaves or the aquarium lid above the waterline; needs a tight-fitting lid and floating cover.
  • Beckford's (Golden) Pencilfish (Nannostomus beckfordi) — to ~5cm. Slim, slow-swimming, upward-angled; competes poorly against fast tetras for food.
  • Common Hatchetfish (Gasteropelecus sternicla) — to ~6–6.5cm. Deep-keeled, surface-dwelling "flying" fish; an excellent jumper needing a very tightly fitting lid, a group of 6+, and floating cover.

Tank & Water Requirements

  • Schooling minimums: Almost every species above must be kept in groups of at least 6, ideally 8–12+, to feel secure and show natural colour and behaviour. Under-stocked numbers are the single most common cause of poor colour, hiding, and fin-nipping.
  • Soft, acidic water: Most South American blackwater species do best in soft, slightly acidic water (pH 5.0–6.8, low hardness); tannin-rich botanicals, driftwood, leaf litter and dim lighting help replicate this.
  • More flexible species: Hardier, whitewater-adapted species (Buenos Aires Tetra, Black Widow Tetra, Bloodfin Tetras, Flame Tetra, Blind Cave Tetra) tolerate a much wider pH/hardness range.
  • Tank size and layout: 45–60cm/34–60L for nano species; 90–120cm+ for larger or more active shoalers. Dense planting, driftwood and subdued lighting reduce stress and are essential for surface-dwellers.
  • Covers: A tight-fitting lid is essential — hatchetfish, bloodfin tetras and Splashing Tetra are all strong jumpers.

Diet & Feeding

Characins are omnivorous micro-predators. Offer a good quality micro-pellet or flake as a staple, supplemented several times a week with live or frozen foods sized for their small mouths — brine shrimp, daphnia, micro/grindal worms and bloodworm bring out best colour and breeding condition, particularly in Congo Tetra, Rummy Nose Tetra and the pencilfish and hatchetfish, which are typically more reluctant to accept dry food. Slow, deliberate feeders (pencilfish) and surface-only feeders (hatchetfish, Splashing Tetra) should not be housed with fast, aggressive feeders.

Temperament & Tank Mate Compatibility

The overwhelming majority of species are peaceful, non-territorial schooling fish that make excellent community tank residents. A small number need a specific compatibility note: Serpae Tetra is the group's best-documented fin-nipper and is not fully community-safe — keep only in large numbers with fast, short-finned tankmates. Blue King Tetra and Buenos Aires Tetra can nip fins if kept in too small a group or underfed. Congo Tetra males carry long, elaborate fins vulnerable to nippers, so pair them with placid tankmates. Pencilfish and hatchetfish are gentle, slow feeders easily outcompeted by fast, boisterous tetras at feeding time.

Breeding Notes

Most tetras are egg-scatterers with no parental care and will readily eat their own eggs and fry, so a dedicated, densely planted breeding tank with fine-leaved plants, dim lighting and soft, acidic water is normally needed. Many species (Neon Tetra, Cardinal Tetra, Rummy Nose Tetra) require very soft, acidic water to trigger spawning, mirroring their blackwater origins. The Splashing Tetra is a notable exception: the pair leap together out of the water to deposit eggs on a leaf or the underside of the lid just above the waterline, after which the male repeatedly splashes water onto the eggs with his tail for 36–72 hours until they hatch. Hatchetfish are rarely bred in home aquaria; most stock is farm-raised in outdoor ponds.

Common Health Issues

  • Neon Tetra Disease (NTD): Caused by the microsporidian parasite Pleistophora hyphessobryconis; despite the name it also affects Cardinal Tetra and many other small characins. Symptoms include restlessness, colour loss in patches, muscle wasting and spinal curvature. No cure exists; affected fish should be removed promptly, and good quarantine practice for new stock is the best prevention.
  • Ich (white spot disease): susceptible especially under temperature swings or stress.
  • Stress-related colour loss/fin damage: under-stocked schools or fin-nippers are the most common preventable issues, particularly for Rummy Nose Tetra, whose colour is a reliable early-warning sign of declining water quality.
  • Jump-related losses: bloodfin tetras, hatchetfish and Splashing Tetra are all strong jumpers — a secure lid is essential.

Sources: SeriouslyFish species profiles, FishBase, Tropical Fish Keeping (Neon Tetra Disease overview).