admin January 19, 2021

One of the more reliable visual methods for determining sex, especially in trout of larger dimensions, is to study the shape of the lower jaw. Females have a shorter and rounded upper jaw, in males the muzzle (snout) is more elongated. Perhaps the most characteristic difference is in the lower jaw. Males have a long and at the beginning of the head back curved jaw resembling a beak (they say that the lower jaw is hook-shaped). Although the length of the muzzle is constantly increasing during the life of females, the lower jaw is never as big as in males.

Some online sources also mention a method of determining sex using anal fin formation. The anal fin is a fin located on the underside of the trout body between the anal opening and the tail fin. Males are said to have a locked fin line “(” while females are said to have the opposite, ie concave “)”. The method is not reliable, but we find it interesting because of the research of the bodies of these wonderful creatures.

We also reviewed the gallery of our catches and it appears that there is a positive association between the beak-shaped lower jaw and the convex shape of the anal fin (males), but not always. The final decision to determine the sex is therefore left to the readers or anglers, and the most reliable determination (without opening the abdominal cavity) could only be done by science. Only DNA analysis can confirm or disprove with certainty the assumption that we caught a male or a female trout.

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