Why is fish the plural of fish? [closed]

Question

What is the etymological and grammatical explanation for the usage of fish as the plural form of fish?

Answer 1

Think of how we use noncount nouns for food: I don’t eat meat or I'll have beef or we’ll have fish for supper. Nobody says that they’re having cows for supper, not unless you plan to invite those cows over for supper and feed them whatever it is cows eat. Even if you said cow not beef, it would still be singular. (And the less said about beeves, the better. :)

So fish, just like so many other nouns of its ilk, found itself being used as a collective singular, thus a mass noun, which therefore took no plural in that context. This type of collective use became so common that this same word came to be used as the normal plural: one fish, two fish, red fish, blue fish.

The OED writes of fish that:

1. b. collective singular used for plural.

These are their two earliest citations:

• a1400 (▸a1325) Cursor Mundi (Vesp.) l. 9395
  Foghul and fiche, grett thing and small.
• ?a1425 Mandeville's Trav. (Egerton) (1889) 57
  Criste..filled þaire nettes full of fisch.

This happens all the time with fishermen, who bring home a catch of tuna or cod or mackerel and such, not the respective plurals of those words. It also commonly happens with game animals: the elk are bugling, the grouse are feeding, the moose are calving, and so and so forth.

So now it sounds wrong to us to use the old plural. That’s why Tolkien put this sentence in Gollum’s mouth in The Lord of the Ring:

What is it they eats? Have they nice fisshes?

Notice how strange all that reads. That’s deliberate.