Each of our yellowfin or silver bream (Acanthropagus australis) is both Arthur and Martha. But not at the same time. Our popular food and angling fish is like many reef fish in that each individual can change sex during its lifetime.

Some fish are of both sexes at the same time (hermaphrodites) because the chance of meeting a fish of one's own species in the huge ocean is bad enough, let alone having to meet one of the opposite sex, in order to breed.

However our bream is a fish that swims in a group or shoal, so it has different survival strategies. If an angler catches a bream the angler should delight in how big SHE is. Or lament how small HE is. After all, bream spend at least their first breeding season as males. Then they change into females (Protandry). This could be so that, as bigger fish, they can create bigger eggs, which once fertile can better withstand the ravages of floating on the surface of the ocean until they hatch. Thus increasing their chances of surviving as a species. It seems to be working because bream are prolific and one of our major food sources.

Scientists still don't know how the genes, chromosomes and hormones of fish such as bream are switched on and off. There are even some fish that can switch back and forth. Now that would be confusing!

Apparently sexual reproduction is necessary in most vertebrates, because asexual reproduction (Parthogenesis) causes a lack of genetic variation as each individual creates identical offspring. If the environment changes and all the members of a species have the same weaknesses then the consequences could be catastrophic for the species. That's probably why so few fish are asexual. Their environment is so changeable. However there are a few creatures, such as starfish, nematodes and fleas who still manage to have the less complicated asexual lifestyle.

There is still so much to learn about the lives and habits of these facinating creatures!