Hello, Walter
Shrimp is a countable noun and has a regular plural: 1 shrimp, 2 shrimps.
At a restaurant, you can order one shrimp cocktail or two shrimp cocktails.
It's like potato salad or apple pie. Even if it takes more than one potato to make the salad and more than one apple to make the pie, you still use those words in singular since they are acting as premodifiers of another noun. 'Potato' and 'apple' are still nouns, but they are occupying the place of an adjective and acting like to one.
Hope it helps.
Miriam