"Cổ" = old or ancient
"Ngư"= fish or some aquatic animals
When I first heard of that Vietnamese word, I thought it was implying an old or ancient kind of fish or aquatic animals. The word sounded great to my ears so that I had grown a bunch of magnificent manifestations, such as one that you're seeing. The nautiluses are used in the pic because of their bizarre looks (at least in my opinion) and the fact that they are historically living fossils, which is related to the "ancient" theme.
However, recently I've found the word "Cổ Ngư" was actually misspelled due to the fact that it's easier to pronounce than the original word: "Cố Ngự" (which means "to fortify").
Painted with Photoshop as usual. Refs loosely used for the nautiluses, anemones and jellies.