Compsaraia samueli, the pelican knifefish,[1] is a species of apteronotid electric fish from the western Amazon basin of Brazil and Peru.

It exhibits pronounced sexual dimorphism in which mature males develop extremely elongated snouts and oral jaws.

[2] This phenotype is found in several other apteronotid species and is used in agonistic jaw-locking behaviors between males.

[3] A study comparing skull shape and jaw-closing performance in males and females of Compsaraia samueli suggested that males with elongated faces for use in fights also had lower mechanical advantages, indicating a trade-off between sexual weaponry and jaw leverage.

[4] Named in honor of the senior author’s father, Samuel Albert, who accompanied his son on an electric-fish collecting trip to Peru, and purchased type specimens from a fish market near Iquitos when he recognized that they differed from all the other electric fishes they had been collecting by the prominent elongate jaws of mature males.