The Blue tetra (Boehlkea fredcochui) has been misidentified and the fish that has been appearing under this name for 40 years in the ornamental fish trade is actually an undescribed species, according to a study published in the latest issue of the journal Vertebrate Zoology by German ichthyologist Axel Zarske.
Describing this misidentified species as Knodus borki (after the German aquarist Dieter Bork), the author distinguished it from Boehlkea fredcochui by the dentition of maxillary bone (three to four tricuspid or conical teeth in K. borki vs. 11 to 21 tricuspid and conical teeth in B. fredcochui), the lateral line (incomplete, with 6"14 scales in K. borki vs. variably complete, with 15"37 scales in B. fredcochui, coloration (B. fredcochui with a black bar-like mark at the caudal-fin base absent in K. borki; K. borki with dark middle caudal-fin rays missing in B. fredcochui; B. fredcochui with a dark longitudinal stripe from the gill cover to the base of the caudal fin while K. borki has a faint dark stripe beginning below the dorsal fin and extending to the middle caudal-fin rays).
Knodus borki is considered to be closely related to K. megalops, but differ in the lateral line (incomplete in Knodus borki vs. complete in K. megalops), the size of eye (2.46"3.24 times in standard length in K. borki vs. 2.2 in K. megalops), the depth of the body in front of the dorsal fin (2.91"3.34 times in standard length in K. borki vs. 2.9 in K. megalops), head length (3.94"4.65 times in standard length in K. borki vs. 3.8 in K. megalops) and colouration. The study also redescribes Boehlkea fredcochui.
For more information, see the paper: Knodus borki sp. n. " ein neuer Salmler aus Peru mit einer ergnzenden Beschreibung von Boehlkea fredcochui Gry, 1966 (Teleostei: Characiformes: Characidae) Vertebrate Zoology 58, pp. 159"171.