We were talking about gender selection in my Dev Bio class today. The instructor use clownfish as an example of organisms changing gender. The order was given as juvenile males to mature males to a dominant female. Basically with the largest fish becoming the female in any given situation.

I had a question that my professor suggested I look up the literature for. Instead I'm going to ask you guys. My question is 2-fold.

1. If a fish is living alone, does it default to male or female?
2. If 2 fish that have differentiated into females are put together, does the small one revert back to male? Or is the 2 females in one location going to lead to survival of the biggest?

Thanks for the help guys!

Default male... but can rise to the occasion and become dominant female if environment and resources are willing.
They can not revert back to male, ever.

Thanks! Biologically that makes a lot of sense, which is probably why it happens.

+1. This is called sequential protandrous ("first male") hermaphroditism. In a group, there is a female with her mate, subordinate males, and then juveniles. Females will probably fight continuously.

One more question... Does anyone know if this change is brought about through hormones or socially. Or if either of these alone is sufficient?

This might be the makings of a little summer research project.

Its pretty much a fill the void - if there is no "alpha" female (social), hormones kick in the sex changes. Oh, btw any clown thats been by itself for six months or more (assuming its old enough to spawn that is) is probably female not male.

Don't take my word for it, go look at the clownfish breeding "bible" by Wilkerson. Pages 134 and 135 to be precise.