Functional analysis of sexual dimorphism in an electric fish, hypopomuspinnicaudatus, order gymnotiformes

Carl D. Hopkins, Nathaniel C. Comfort, Joseph Bastian, Andrew H. Bass

Research output: Contribution to journalArticlepeer-review

88 Scopus citations


Hypopomus pinnicaudatus. an electric fish, has a marked sexual dimorphism in its tail filament. Sexually mature males have long, ‘feathered’ tails as compared with females. The sexual dimorphism emerges when a fish reaches about 110 mm total length. Mature males have larger electrocytes which are more widely spaced and more numerous than those in mature females. The biphasic electric organ discharge (EOD) is longer in males than in females. The peak-to-peak amplitude of the male’s EOD is weaker than a female’s of the same total length. The weaker discharge is unexpected given the increase in size and number of electrocytes. It is suggested that the reduction in EOD amplitude is a consequence of the increase in EOD duration among males. Further, female choice probably played a role in the evolution of long duration EODs among males, and males may have secondarily grown long tails to compensate for the loss in active space that would otherwise accompany a weaker EOD.

Original languageEnglish (US)
Pages (from-to)350-367
Number of pages18
JournalBrain, behavior and evolution
Issue number6
StatePublished - 1990
Externally publishedYes


  • Electric communication
  • Electric fish
  • Electric organ
  • Electric organ discharge
  • Electrocyte morphology
  • Female choice
  • Sex difference
  • Sexual dimorphism
  • Sexual selection

ASJC Scopus subject areas

  • Developmental Neuroscience
  • Behavioral Neuroscience


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