Juvenile patterns in genus Haemulon
The Grunts (family Haemulidae) are some of the most fun fishes to catch in tropical waters all around the world. They are often small, tasty, voracious and beautiful species that can make any angler happy (mostly the youngsters: they love the "grunt" noise!).
But their identification is sometimes tricky, as their pattern and color can change during their life cycles and considering their diet.
Here is an excellent study of the problem: Ontogenetic diet changes and food partitioning of Haemulon spp. coral reef fishes, with a review of the genus diet. If you are not fond of scientific vocabulary, stay with the pictures ;)
For other identifications, see this page.