Pterygoplichthys, sometimes collectively known as janitor fish, is a genus of South American armored catfishes.[1] These fish are commonly known as sailfin armoured catfish or sailfin plecs, especially in the aquarium trade.
Pterygoplichthys is derived from the Greek πτέρυγ- (pteryg-), meaning "wing", (hoplon) - weapon and ἰχθύς (ichthys) meaning "fish".
Pterygoplichthys has undergone much shifting in the past decades. Previously Liposarcus, Glyptoperichthys and Pterygoplichthys had been named as separate genera.[2][3] Since then, these genera were recognized as synonyms of Pterygoplichthys by Armbruster, as the few differences between the genera were not deemed great enough to validate Glyptoperichthys and Liposarcus, and that recognizing these separate genera would leave neither Pterygoplichthys nor Glyptoperichthys as monophyletic.[4][5]
Pterygoplichthys can be differentiated from most other loricariids due to their large dorsal fins with 9 or more (usually 10) dorsal fin rays, which gives them their common name "sailfin catfish".[7] These fish have rows of armour plating covering the body; the abdomen is almost completely covered in small plates.[5] Other characteristics of members of this genus include an underslung suckermouth, evertable cheek plates, adipose fin present, and an enlarged stomach connected to the dorsal abdominal wall by a connective tissue sheet. P. anisitsi, P. disjunctivus, P. multiradiatus, and P. pardalis lack cheek odontodes, but still possess the evertible cheek plates; this was previously used as a trait to determine these fish as part of the genus Liposarcus.[5] Species of the P. gibbiceps group (species formerly classified in the genus Glyptoperichthys) are easily recognized by a large crest above the back of their skull.[5]
Color pattern is generally dark brown with either darker spots or lighter spots or vermiculations.[5] The adult size of a member of Pterygoplichthys can range from about 50–70 cm.
The stomach of Pterygoplichthys is greatly expanded with the posterior portion forming a long, thin sac that is highly vascularized.[8]