Left: The 'hump' is more pronounced on the male fish.

In some species, male and female fish have different standard weight curves.

Most male fish have two testes of similar size.

But when male fish saw other males, they began opening their mouths in yawns.

But recently fishermen have been getting orders for the male fish.

The male fish has a deeper body, and differs significantly in colouration.

A male fish whose eye was gouged out by a fisherman's hook.

These male fish are substantially larger (sometimes up to 60 times) than their female counterparts.

Basically, the larger the male fish, the bigger the adaptive benefit.