Why don't young fish look like adults?

You look just like your father! In some tropical fish this is a phrase you will never hear, if fish can speak at all.

In fact, in some fish, juveniles bear so little resemblance to adults that it is doubtful whether they belong to the same species.

Why do they change so much between birth and adulthood?

It's not just a matter of coquetry; the differences in morphology and colour are essential to their survival.

Escaping predators by blending into the background

By displaying dull colours or a body that blends in with its surroundings, the juvenile escapes predators.

Camouflage and mimicry are techniques that enable juveniles to go unnoticed.

The batfish Platax orbicularis is a good example. As a juvenile, this fish resembles a leaf floating on the surface of the water.

Not being seen as a rival

The morphological difference between juvenile and adult fish is a means of ensuring the survival of the species. Because they do not resemble adults, juvenile fish are not seen as rivals by adults of breeding age.

The yellowbar angelfish Pomacanthus maculosus has a striped pattern on its body that disappears when it reaches adulthood, giving way to a solid blue coat with only a yellow spot.

In some territorial species, juveniles do not have the same appearance as adults and are therefore not considered to be competitors.

Adapting to the environment

Juvenile fish do not necessarily live in the same environment as adults.

Juveniles often go through a pelagic phase before reaching the coral reef and lagoon. Their morphology is adapted to their lifestyle and feeding habits.

Juvenile Chaetodon auriga butterfly fish

Cover photo: juvenile Platax orbicularis.

Photo credit: Olivier Dugornay (IFREMER, Pôle Images, Centre Bretagne - ZI de la Pointe du Diable - CS 10070 - 29280 Plouzané, France), CC BY 4.0 via Wikimedia Commons;