Hello again from Alkor! We are on day 9 of our research cruise in the Baltic Sea and today we would like to tell you more about the flatfish world.

But let’s start from the beginning. Have you heard about metamorphosis before? It describes the transformation of a body form and structure after hatching, just like the famous caterpillar transforming into an adult butterfly. Metamorphoses are also common in the aquatic world, and in this regard, flatfish hold some truly unique developments.

After hatching, flatfish start their lives as pelagic larvae with an eye on each side of the head. But then metamorphosis kicks in. The body starts to flatten, and one eye migrates to the side which then becomes the “eye side” of the fish. A growing bone prevents the eye from moving back. With this new body, the flatfish is now well prepared for its life as a benthic fish on the bottom of the Baltic Sea.

During our cruise we get to see flatfish at every stage: egg and pelagic drifting larvae during our plankton sampling (with the Bongo net) and bottom-settling juveniles and adults during our fisheries surveys (Fig. 1 & 2). So maybe next time you see (or step on) a flatfish in the Baltic Sea, remember, behind its odd appearance is a truly remarkable life history.

Greetings from on board RV ALKOR, Anna and Georgia