Catfish of the Month Right September 2002

Pterodoras granulosus
Granulated Catfish, Armado (Venezuelan), Bacu (Brazilian), Common Bacu, Ru Tornmalle (Denmark) - Pterodoras granulosus   (Valenciennes, 1821)

Article © Chris Ralph, uploaded September 01, 2002.

This month sees another scoop in the catfish of the month article section. Chris Ralph takes time out from answring catfish queries for Practical Fishkeeping Magazine and judging catfish to write about this gentle giant of the amazon waterways. Here is what he has to say.

The Common Bacu or Pterodoras granulosus is another of my favourite large catfish, which I currently have the pleasure to keep. At the moment I have three of these "gentle giants" housed within my 12' x 3' x 4' tropical pond. They vary in size from approximately 600mm (24") to 900mm (36"). Two well-known "Catfish Fanatics" initially purchased all three catfish at the same time in the South of England - Tony Tyson and Terry Wilkins. I was asked to rescue one of these catfish from Terry as it had outgrown its accommodation namely a 72" x 24" x 24" aquarium. At the time of its transfer to my tropical pond it was approximately 20" total length, some two and half years later this fish is closer to 36" total length. This catfish was given the name "Well Ard" and the name has stuck. (For our international audience I should point out that "Well Ard" alludes to the fishes hardy nigh on indestructible nature - Ed). I quite often get people asking me how Well Ard is doing. I purchased the other two catfish from Tony and introduced them to the pond a couple of months later when they were approximately 6" in length. These two fish are now approximately 24" long and are eating anything that is offered to them including catfish pellets, floating food sticks, pond pellets, whole prawns, mussels, cockles and earthworms.

My observations of these fish suggest that I might have two females and one male, as I have two rather fat catfish and one, which is more slender. I have not seen any obvious signs of spawning activity to date, but these catfish are quite happy to swim around the pond together. Of the three catfish Well Ard is perhaps the tamest of the three allowing me to feed her by hand! These catfish are kept in with a number of other large catfish including Pseudodoras niger, Megalodoras uranoscopus, Leiarius pictus, Auchenoglanis occidentalis and numerous Synodontis species. Due to the size that these catfish can attain keeping them in anything smaller than a 72" x 24" x 24" aquarium should not be considered, and it should be pointed out that even this size aquarium is really a little too small!

Whilst fish collecting in Peru two years ago with a number of members of the Catfish Study Group (UK) including Jools & Clare Dignall, Allan James, Giles Barlow, Robin Warne, Steve Pritchard, Terry Wilkins and Alan Appleton, we caught a couple of these catfish on rod and line. They were to spend the next few days on board our accommodation for the week, only to be returned to the point at which they were caught originally. I decided that the three specimens that I had at home already were enough and that they would be better off swimming in the Amazon! In South America the local inhabitants would catch and eat these catfish, and as you can imagine a large specimen would feed a whole family for a few days. Seeing these catfish in their natural habitat was an amazing experience, one that will live with me for a long time to come.

The author and Pterodoras granulosus
The author and Pterodoras granulosus
Pterodoras granulosus
Close up of the catch

The common bacu are found throughout the river systems of South America. The colour pattern of these catfish varies depending upon the location that they originate from. These fish are usually a muddy-brown colour with some darker spots over the body and fins. As these fish mature the spotting tends to fade. Juvenile specimens tend not to be as dark coloured as adult fish, in fact the two specimens caught in Peru were light brown/tan in colouration. The body of these catfish is best described as being robust. The body is naked i.e. it is devoid of scales, but the skin is very thick and tough. There are between 23 and 28 shallow lateral plates known as scutes along the length of the body. Their eyes are very small in comparison to the rest of the fish and they have three simple pairs of barbels. They have a deeply forked caudal fin, which also helps to distinguish this fish from other large Doradids. In their natural habitats these catfish are migratory, shoaling in large numbers as they make their journeys upstream to spawn.

Copyright information for the images used in this article can be found on the species' full Cat-eLog page.

Down Cat-eLog Data Sheet
Scientific Name Pterodoras granulosus  (Valenciennes, 1821)
Common Names Granulated Catfish
Armado (Venezuelan), Bacu (Brazilian), Common Bacu, Ru Tornmalle (Denmark)
Type Locality South America.
Synonym(s) Doras granulosus
Pronunciation gran you LOW sus
Etymology Pterodoras: From the Greek pteron, meaning fin, and doras, meaning skin (also a word commonly used in forming generic names for doradids); in reference to the forked caudal fin. 
Down Species Information
Size 700mm or 27.6" SL. Find near, nearer or same sized spp.
Identification The colour pattern of these catfish varies depending upon the location that they originate from. These fish are usually a muddy-brown colour with some darker spots over the body and fins. As these fish mature the spotting tends to fade. Juvenile specimens tend not to be as dark coloured as adult fish,
Sexing There are no reported external sexual differences. Personal observation shows that females tend to be more heavily built/robust than the males, which tend to be slender. There may also be differences associated with the structure of the head as with the Synodontis catfish, but further observations need to be made.
Down Habitat Information
Distribution South America: Amazon and Paraná River basins and coastal drainages in Guyana and Suriname.
Amazon (click on these areas to find other species found there)
La Plata, Paran√° (click on these areas to find other species found there)
La Plata, Uruguay, Lower Uruguay (click on these areas to find other species found there)

Log in to view data on a map.
IUCN Red List Category Least Concern, range map and more is available on the IUCN species page. Last assessed 2020.
pH 6.4 - 7.6
Temperature 20.0-24.0°C or 68-75.2°F (Show species within this range)
Other Parameters Wamer water will be tolerated at least for a period of time. It is documented that keeping these fish in water with a pH value above 7.5 can cause skin and eye cloudiness.
Down Husbandry Information
Feeding Omnivore feeding on a very mixed and varied diet including catfish pellets, earthworms, whole prawns, mussels, floating sticks/pellets and snails. In their natural environment they would feed upon snails, aquatic plants and fruits.
See also natural feeding behaviour paper in the references section. User data.
Furniture Large pieces of bogwood are ideal. Large diameter pipe can be used but it should be large enough for the catfish to easily fit in without becoming stuck. I have managed to create two shady areas within my tropical pond, by covering the ends with decking, where these catfish prefer to hide until feeding time.
Compatibility Ideally suited to life with other large fish. These catfish are not predatory but would mistakenly take a smaller fish if hungry.
Suggested Tankmates Other large catfish such as Leiarius, Megalodoras, Oscars and larger characins.
Breeding There are no known aquarium spawnings of this catfish. This is most likely due to the size that these fish can attain and hence the subsequent size of aquarium in which to spawn them.
Breeding Reports There is no breeding report.
Down Further Information
Reference Voyage de Humboldt et Bonpland v. 2 (Title page 1833), pp 184.
Registered Keepers There are 28 registered keepers, view all "my cats" data.
Wishlists Love this species? Click the heart to add it to your wish list.
There are 4 wishes to keep this species, see who wants what.
Spotters Spotted this species somewhere? Click the binoculars!
There are 16 records of this fish being seen, view them all.
Forum BBCode
Search for P. granulosus
Look up Look up P. granulosus on
Look up on Fishbase Look up P. granulosus on Fishbase
Look up on Encyclopedia of Life Look up P. granulosus on Encyclopedia of Life
Look up on Global Biodiversity Information Facility Look up P. granulosus on Global Biodiversity Information Facility
Pterodoras granulosus QR code LFS label creator
ARN ref:
Last Update 2020 Sep 19 01:40 (species record created: 2002 Sep 01 11:22)

Back to Catfish of the Month index.