Translation:There is one shrimp left on his plate.
I think that "There is still a shrimp on his plate" is much more natural English than "There remains a shrimp on his plate". Also, "prawn" not just what is mainly an Americanism with "shrimp"
Technically, a prawn is "une crevette rose". A shrimp is "une crevette (grise)".
The literal in-vs.-on thing doesn't work when crossing the language barrier. In English, something is ON the plate (not "in" the plate). In French, it is "dans" l'assiette (not "sur l'assiette").
Hi Barbara, you are correct. "Assiette" is indeed feminine, but it begins with a vowel, so "son" must represent the possessive.