Koi Gender Identification


Until a Koi is over 10-12” or 2 years of age, it is very difficult to determine whether your Koi is male or female. The bigger or older it is the easier it can be. You need to put several of these clues together to give yourself a higher percentage of success:

  • Body: Males tend to be slimmer and the females more plump, especially near to spawning.
  • Pectoral fins: Male fins are more pointed and the females more rounded and generally clearer or opaque.
  • Gill plates: On the male the gill plates should be quite noticeably rough to touch.
  • Near spawning time: On mature males tubercles will appear on the head, flanks and tail of the fish. This can be mistaken for white spot so you need to be sure.
  • Behaviour: Females are generally more friendly and easily enticed to hand feed, as the males can be a little untrusting, however this is not a big percentage of fact. Also a fish chasing or bothering another fish at spawning does not necessarily mean it’s a male after a female. Males will harass other males at this time so again not conclusive
  • Hands on: This would be a more conclusive method of sexing your fish. I would recommend sedating your fish unless you’re very confident in handling. Turn the fish upside down, the female will clearly have 2 vents before the anal fin and near spawning it will have a pink fleshy protruding vent.

Does it really matter?
Most general fish keepers may not even notice if their fish have spawned, even if they have! And it makes little difference to them what sex it is when buying a new fish. It can be quite concerning if you have a lot more male’s than female’s, as when spawning happens this is where injury or sometimes death can occur with the ferocity of too many male’s pushing a female around. Obviously breeders or if you intend to try breeding then it’s all important. Also if you’re thinking of showing your Koi to a good standard, sex is quite important as most of the champions are female as they are a bigger and better shaped to show off their patterns and colours.

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