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Peculiarities of the sex determination system in clownfish

765 views · Published 20 January 2017 · 6:40 · Indexed 8 October 2026

Channel: Nikolay's Genetics Lessons · 2017 · Education

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First, to be clear, all clownfish are born gender neutral. They are not male nor female at birth and as juveniles. The other thing that makes sexing Ocellaris Clownfish difficult is that they can become male and then female. This means that a juvenile clownfish can turn into a male, and the same clownfish can later change sexes to become a female. Once they become female they cannot change back to male.

This is how the social hierarchy works for clownfish: There is one dominant female clownfish, partnered with a male, who is the next most dominant fish. The female is larger (often much larger) than the male. Next are non-mating males and juveniles. They are usually smaller still than the dominant male. If the male mate were to die, the next dominant male would become the mate (if the female accepts him). If the female were to die, then the dominant male would change to female and the next male in line would become the mate.

Of course, that is in a perfect world, the open reef. In our tanks it is not always that simple. If you introduce two fish at the same time then one will likely become the female and the other male. This does not guarantee that they will mate. You will be able to tell which is the female because she will be much more aggressive. Often, the female will barely let the male eat and sometimes will almost control where in the tank the male is allowed to go. This will go on until the male submits or is killed by the female.

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