Start with the fish at the back of the card. Yellow+Blue=Green. Green fish do actually swim through the waters on the front of the card, whereas blue and yellow fish don’t.
If you read the letters on all the green fish from left to right, top to bottom you should be able to read five coherent words. Don’t mind some fish sticking out of the line a bit, fish never swim in a straight line. The words you should find are the following: ‘THE LANGUAGE OF THE SEA’.
Look for ‘the language of the sea’. A radio code language does not make sense, as the puzzles on this card are quite visual. This card uses the Semaphore alphabet. That is the alphabet with the yellow/red flags. Keep this in mind.
The letter square should provide you with the guidance you seek. If you hold the card up to the light, you should see the weird-shaped seaweed shine through. It will indicate the letters P, U, R, P, L and E in the letter square. Now we know that Purple Fish give guidance.
In the semaphore language, you use the body of the person that is holding the flags as an anchor point (pun intended). We do not have that on this card however, so we should be looking for another element that provides that guidance. The purple fish make for a good candidate, as they swim in a straight line. The clue we found in the previous step shows you that you are on the right path. The purple fish are your human bodies in this use of the semaphore alphabet.
Around every row of purple fish swim two red fish with yellow fins. These are your flags. If you see the top fish as the head, middle fish as the waist and bottom fish as the feet, they give you a decent anchor point. Translating these combinations with the semaphore alphabet should give you the letters C, L, O, U and D. Together, they form the solution word of this card ‘CLOUD’.