These are Chinese characters of different colors and one word below each word - these are "wealth", "lucky" and "good luck". There are red envelopes and koi in the pond (this is a symbol of wildness and the biggest payment).
If you play the classic or luxury version, the main rewards of the game are very similar, although the luxury version is more comprehensive. You will trigger this by hitting 3 gold coins on the reel. The classic version allows you to choose one of the five koi - this will let you know where the slot's title comes from! Each of the five koi looks the same, but with a different colored background. Your first choice is to have 25 free games, each of which will see any victory using the Koi wild symbol multiplied by 2x, 3x or 5x. The other four options reduce the number of free spins available.