Colomesus Asellus Pufferfish Care Sheet

Updated: 5 days ago

This care sheet is written with the aim of providing the optimal care for this species of fish.

Pufferfish Enthusiasts Worldwide endeavours to inspire and promote the highest standards of care - not basic or minimum care - using the best evidence available at the time.

The asellus is a species of freshwater pufferfish, from the Colomesus genus, which is endemic to tropical South America.

This C.asellus is a popular aquarium fish and is commonly referred to as the Amazon Puffer, Peruvian Puffer and the South American Puffer (sometimes abbreviated to SAP).

Owing to the convenient size and social nature of this pufferfish it has become very popular with keepers across the world.

In the wild

The distribution range of C.asellus includes the Tocantins River basin, as well as in numerous other rivers in South America.

The water chemistry within the distribution range of this species is variable and they can be found in both soft, acidic waters and hard, alkaline waters.

Mayfly nymph

The Colomesus asellus can be classified in its trophic ecology as an insectivore. In the wild, this species eats a variety of benthic prey, but their diet is mostly comprised of Ephemeroptera nymphs (known as mayfly, fishflies and shadflies). They also eat Chironomidae (known as non-biting midges), other insects, gastropods (snails) and plant/algae matter.

In the aquarium

Imports of wild-caught C.asellus are very common due to their popularity as an aquarium fish. Breeding this species in captivity is unfortunately very labour and resource-intensive, which would make captive-bred examples very expensive compared to wild-caught specimens. Therefore, any commercial breeding attempt would likely be economically unviable.

This pufferfish requires highly oxygenated water with a medium to strong flow. The strength of the flow in the aquarium is usually achieved with spray bars from canister filters, angled towards the top of the water. Keeping a slightly dropped water level, so that the returning water from the filter splashes down onto the surface, creates agitation and facilitates a gas exchange for high levels of oxygenation.

Powerheads with narrow gaps in the grill may be used to create additional flow. We would advise that cages or guards (such as anemone guards) are used on powerheads to prevent injury to the fish if they become trapped.

The tank decor (scape) should offer the fish plenty of open swimming space and areas to hide at night.

Densely scaping only the back of the aquarium strikes this balance and will encourage the fish to use the front of the aquarium. Driftwood, water-logged mangrove roots, Mopani wood/roots and smooth boulders/rocks can be utilised in the aquarium for this purpose.

Group size

Group size is very important for this species.

The C.asellus is found within large shoals in the wild and should always be kept in groups consisting of at least six individuals.

This species displays signs of severe stress and anxiety when they are housed alone - as a single specimen - or in groups less than six.

Their behaviour in these circumstances has been described as ‘neurotic’.

Insufficient group sizes can also cause extreme aggression.

When kept in appropriately sized groups, they are much more confident, relaxed, have a better appetite/feeding response and enjoy a longer life.

This is owed to the sense of security and social stimulation they receive as part of a shoal.

Tank size

The C.asellus is an active species and they will spend much of their time travelling the length and breadth of the aquarium. For this reason, they should be housed in a tank of at least 100cm (39.37 inches) in length.

Our recommended tank size is at least 200 litres (52.83 US gallons) long for the minimum group of six, with additional space for further stocking.

Water values

Maintain the following water parameters:

  • PH: 6.0 - 7.2

  • Temp: 22-28c

  • N03: below 15ppm (as close to zero as possible)

  • NH3/NH4+: 0ppm

  • N02: 0ppm

  • GH: 4-15 dGH


Although the C.asellus is considered to be one of the most 'peaceful' pufferfish species by many in the trade, it is not suitable for the typical community aquarium, despite advice to the contrary on some areas of the internet.

Research into their natural diet has shown that the stomach content of wild-caught individuals include small amounts of fins and scales from other fish and anecdotes from keepers often include caveats of this species nipping the fins of some other fish if given the opportunity.

Other fish can be kept alongside this species of pufferfish, but allospecifics (members of a different species) must be very carefully considered. Any potential tankmate must be non-aggressive, fast-swimming, short-finned and able to thrive in the same water values. This rules out fish like guppies, angelfish, gourami and Betta.

Hemigrammus rhodostomus (Rummy-nose tetra)

Providing that the water values are suitable and that the aquarium is mature enough to support a group, species of catfish from the Otocinclus genus may be used in the C.asellus tank for minor algae control.

Also, dependant on water values and tank size, C.asellus can be housed with groups of Hemigrammus rhodostomus (Rummy-nose tetra), Paracheirodon axelrodi (Cardinal tetra) and other similar fish.

Notable behaviour

They are very intelligent and will beg their owners once they have made the association between humans and food.

As this species is a very active swimmer, they can be observed frequently swimming the length of their aquarium. However, if these fish are stressed, their swimming by be erratic. This behaviour is commonly referred to as "glass surfing".

Sexual dimorphism

There is no known method of determining the sex of this species for the home aquarist.


One of the most important elements in keeping the C.asellus is providing a varied and balanced diet, in order to ensure that their nutritional needs are being met.

When housed correctly, this species typically has a very good appetite and is therefore much more forgiving and less picky than other species, even accepting pellet and other prepared foods.

Our preferred foods for these fish include:

  • Small snails - read below

  • Small earthworm

  • Small insects (Aphids, small crickets, small cockroaches and woodlice)

  • Quality pellet food (such as JBL NovoGranoColor, JBL GranaDiscus, JBL GranaCichlid)

  • Repashy - Grub PieFish

  • Repashy - Soilent Green

  • Fluval® Bug Bites

  • Bloodworm (rarely)

This species should not be offered cockles, mussels, clams, oysters or similar mollusks.

Feeding hard-foods and teeth maintenance

A sedated C.asellus with overgrown teeth.

The C.asellus have very fast growing teeth, so it is absolutely essential that the keeper of this species offers hard-foods on a daily basis.

Feeding hard foods, such as the pellets mentioned above, and employing the methods under 'Tips to help' (below) are the easiest and most practical ways of ensuring that the fish's teeth remain at a healthy length.

Failure to provide hard-foods regularly will quickly result in serious dentistry complications that will require intervention by either the competent aquarist or a veterinary professional.

If you intend on keeping this species then you may be told that you will have to familiarise yourself with the process of trimming their teeth. The truth is that overgrown teeth are very easily avoided by feeding the correct type of foods and removing the need of having to intervene in the first place should be the priority. Simply put, if the keeper is having to have the fish's teeth trimmed periodically then their puffer's diet needs revising.

Snails alone will not maintain their teeth

Although snails are very nutritious, they shouldn't be relied upon solely for teeth maintenance. Culturing enough snails to maintain the teeth - of at least six C.asellus - can be very challenging, so the hard-pellets are the perfect substitute.

It is recommended that keepers of this pufferfish breed aquatic snails in a separate system so they can offer snails as a part of a varied diet. Maintaining a high mineral content (using buffers if necessary) in the water of the snail breeder can help the keeper in developing shells of the desired hardness.

This pufferfish certainly prefers some species of snails over others. I like to feed snails that contain a substantial amount of meat, such as Physella acuta (bladder snail). Various species commonly referred to as ‘ramshorn snails’ and small/young terrestrial snails that are cultured for reptile and human consumption also work well.

Tips to help

In addition to feeding hard pellet foods, the keeper can also utilise the highly nutritious foods from Repashy by smearing the mixture onto rocks and then submerging those rocks into the aquarium. The pufferfish will 'scrape' the food from the rocks with their teeth.

The C.asellus is believed to do this in the wild, scraping algae from stones and rocks in their natural habitat. I have included Repashy Soilent Green in the list of preferred foods because it is essential that they receive plant matter from their diet.


This pufferfish is intolerant of poor water conditions, so a high level of biological and mechanical filtration is needed to deal with the amount of waste that this fish produces. Good filtration combined with excellent husbandry is essential to the health of this species. Frequent water changes must be carried out to maintain N03 (nitrate) levels below 15ppm, or as close to zero as possible.


C.asellus can inflate themselves when frightened or stressed.

They should never be provoked into inflating!

If the fish needs to be moved for whatever reason, it should be herded into a watertight container under the surface of the water to prevent it from inhaling air.

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