Amazon Puffer

About

Most "freshwater" puffers on a shop shelf are not freshwater fish. The green spotted puffer we also list is an estuary animal whose salinity has to be raised as it matures, and a life spent in tap water is a short one. The Amazon puffer is the genuine exception. Wikipedia records that it "has typically been recognized as the only true freshwater pufferfish of South America" and that it "is normally only found in freshwater environments although it will tolerate slightly brackish water"; FishBase files it as freshwater and demersal, "found mostly in freshwater and coastal streams, but can tolerate brackish water"; and Seriously Fish separates it from its coastal congener C. psittacus by its "predominantly freshwater, fluvial (vs. brackish, coastal) ecology". So: no marine salt, no rising specific gravity, no aragonite. What it wants instead is clean, moving, oxygen-rich river water — Seriously Fish notes it is mostly collected from high-oxygen habitats and may be sensitive to low oxygen, and Maidenhead Aquatics warns it is "prone to whitespot when kept in aquaria without high oxygen levels or rapid currents". The second surprise is that it shoals. Nearly every other freshwater puffer is a solitary bigot; this one "naturally forms loose aggregations and can behave nervously in the absence of conspecifics" (Seriously Fish), and Aquarium Co-Op is blunt about the arithmetic: "They are best kept either as an individual or in a group of six or more. If you decide to go with a number somewhere in between, they could start fighting and get into territorial disputes." Two or three is the one number that does not work. The third thing is the reason this page exists. Tetraodontids have no true teeth: the jawbone itself is modified into four fused plates, and Seriously Fish says of them, "These grow continuously at a surprising rate." Wikipedia goes further and states that this species "has some of the fastest growing teeth of the freshwater puffers, so feeding crunchy foods and possibly having to do dentistry are two important factors". Aquarium Co-Op spells out the ending: "your puffer's teeth may become so overgrown that they can no longer properly eat. To prevent them from starving, you need to clip the tips of their teeth" — a clove-oil sedation and a pair of cuticle cutters, "every 4-12 months" depending on diet. This is not folklore. A puffer fed on bloodworm and pellets will look healthy for a year and then quietly stop being able to close its mouth on food. And it is a puffer, which the shop shelf never mentions. Seriously Fish's profile states that "Puffer flesh is toxic and can cause clinical poisoning and human mortality", with the agent "usually either tetrodotoxin or saxitoxin" depending on species, area and season, and says of this genus that "Colomesus species accumulate saxitoxin, although it is unclear whether eating their flesh represents a danger to humans". Wikipedia is specific for C. asellus: "It is known to contain the toxin saxitoxin, and gonyautoxin such as the GTX 2 and GTX 3." Neither source says handling a live one is dangerous and this entry does not claim it is — but a dead puffer is not ordinary tank waste, so net it out rather than leaving it to be scavenged. Size claims vary and it is worth knowing why. FishBase gives 12.8 cm SL as the wild maximum; Seriously Fish repeats that figure and adds "aquarium reports suggest 70 – 80 mm to be typical"; Maidenhead lists 8 cm; Aquarium Co-Op calls it a 7.6 cm fish in its care guide and a 10 cm fish in its puffer round-up. This entry uses 10 cm as the size a well-kept adult reaches. Note also that FishBase and Maidenhead now file the species under Sphoeroides asellus, while GBIF, Seriously Fish, Wikipedia and the trade keep it in Colomesus — same fish, two shelves.

Care

One fish or six, never a handful in between. Give a group at least 150 litres over a 120 cm base. Seriously Fish specifies base dimensions of 120 x 30 x 30 cm for long-term care (its own filter note calls that 108 litres) and Wikipedia says at least 109 litres, but neither figure has a fish count attached to it; the one source that puts a number against this group size is Aquarium Co-Op's puffer round-up, which asks for "a group of six or more in a 40- to 55-gallon planted tank or larger" — 150 to 208 litres. Its care guide phrases the same advice as "at least a 30-gallon aquarium, but 55 gallons would be even better". Straight fresh water, soft to medium, pH somewhere between 6 and 7.5, warm, and above all moving and well oxygenated: add a powerhead and over-filter. Plant it heavily — Co-Op suggests tall background plants like vallisneria as swimming obstacles — and break the sight lines with wood, because Maidenhead notes that "conspecific fin-nipping will also occur in cramped aquaria". Tankmates must be fast, short-finned and similar-sized: mollies, swordtails, larger tetras and rasboras, dwarf cichlids, Danio and Devario. Shrimp and snails are food, not company. Every shop fish is wild-caught, often thin and carrying parasites, so quarantine before it meets anything.

Diet

Hard-shelled food several times a week is what keeps the ever-growing beak in check: snails, small clams and cockles, shell-on prawn, crab leg, freeze-dried krill. Frozen bloodworm, mysis and live blackworm are for putting weight on a new import and do nothing for the teeth. Leave some algae on hard décor — Seriously Fish suggests aufwuchs form a real part of the wild diet. Watch the beak; an overgrown one has to be clipped or the fish starves.

Telling males from females

What works for this species, most reliable first.

• Adult sizeA hint only · only across animals of the same age

  In many cichlids, catfish and loaches one sex simply grows larger — usually the male, though there are well-known reversals.

Similar species

Same category and the closest water parameters — if this species isn't quite it, start here.

Sold in Lithuania

These Lithuanian shops listed this species in their public catalogue (checked August 8, 2026). Stock moves — ask before you travel.

These links are unpaid: we get nothing for them and ask for nothing.

Frequently asked questions

What tank size does a Amazon Puffer need?

A Amazon Puffer needs an aquarium of at least 150 litres (39.6 US gallons) with a footprint at least 120 cm (47.2 in) long — for this species, swimming length matters as much as raw volume.

What water parameters does a Amazon Puffer need?

Amazon Puffer does best at 20–28 °C (68–82.4 °F), pH 5.5–8 and a general hardness of 2–15 °dGH.

What group size does a Amazon Puffer need?

Amazon Puffer is a social species — keep a group of at least 6 so natural behaviour emerges and stress stays low.

Is the Amazon Puffer suitable for beginners?

Amazon Puffer is a demanding species best attempted with some experience — it needs stable, closely watched conditions to thrive.

Sources

• FishBase — Sphoeroides asellus (Amazon puffer)
• Seriously Fish — Colomesus asellus (Amazon Puffer)
• Wikipedia — Colomesus asellus
• Aquarium Co-Op — Care Guide for Amazon Puffers
• Aquarium Co-Op — Top 10 Pufferfish You Can Keep in Freshwater and Brackish Aquariums
• Maidenhead Aquatics — South American Puffer (Sphoeroides asellus)
• GBIF Backbone Taxonomy — species-match API for "Colomesus asellus"