What Nemo Did Next

Recent conversations with a banker and a lawyer (to be) have reminded me that the little fishy world I inhabit is in fact unutterably cool and interesting, and that most people don't know that much about it, and therefore it is bloggable! Ha. You spend your days in the office reading paper after paper after paper, and occasionally you get excited by something stupidly esoteric that only your supervisor would also get excited by (you hope), and you forget that the basic facts of the system are really pretty fascinating in themselves.

What Nemo Did Next, if he had a long and happy life, is that he turned into a woman. Quite a lot of marine fish are sequentially hermaphroditic, changing sex either from female to male or from male to female at some point in their lives. Nemos (or more accurately the clown anemonefish Amphiprion percula) are a particularly well-studied system due to some funky guy who figured it all out whilst living in Madang Bay in Papua New Guinea, isn't the marine biologist's life a tough one? These clownfish live in anemones, as you know, and in each anemone lives a little social group -- the largest fish is female, the second largest male, and all the rest don't actually breed. There is a really strict linear hierarchy based on the relative sizes of the fish in the social group, so the female is Top Fish, followed by the male (clownfish have got it right!), followed by the rest in decreasing size. When the female dies, everybody else grows quickly and moves up a rank: no. 2 changes sex from male to female, no. 3 becomes the breeding male, and every one else is one step closer to the Top Fish Position. So if you think about it, Marlin (Nemo's dad) should really have turned into his Mum within a few weeks of his Mum being eaten by the big scary barracuda. Not that his Mum was his real Mum anyway, he was adopted, because when the eggs hatch (after being very very carefully tended for 2-4 days by the father and not the mother -- did I say something about clownfish getting it right?) the larvae just get swept away by the current and eventually when the baby fish get big enough they pick a random anemone to join -- hardly likely to be the one they came from originally.

But you know, I love the film, and they got the coral looking quite realistic, so I don't really mind that they didn't try to explain to all these kids that what Nemo really wanted to be when he grew up was, well, a girl.

P/S Lots of other fish do it the other way round, with females turning into males, especially when the males need to be big and powerful in order to maintain harems of females. So when you are small, you might as well be female so you can reproduce a little bit; when you get bigger you change sex into male so you can reproduce a lot (by mating with lots of females in your harem). Currently I'm hoping to study some fish which do this. It's very cool because some females, instead of patiently waiting to move up the hiearchy step by step towards big male-ness, try to employ alternative strategies like changing sex earlier and hanging around as a small bachelor male, growing quickly (not using any energy on producing eggs as a female) to a size where they are big enough to compete for harems; or changing sex and trying to sequester some of the harem's females for themselves so splitting the harem, etc. etc. And it's even cooler because more and more such fish are turning out to be able to reverse their initial sex change, which brings up all kinds of other questions about whether a small male might give up and change back to female.

So anyway really my PhD is about how fish try to have as much sex as possible. If you think about it. Hmm.