Please tell me the plural of fish. In the dictionary it says plural is fish or fishes. When I look in the encyclopedia they use the term fishes a lot.
"Fish" is one of those odd words that's usually both singular and plural—like "deer" and (in Canada) "beer." So we can say:
We caught five fish.
We saw three deer.
We Canadians drank six beer. (See my additional comments in the continuation of this post.)
But we can use "fishes" when we are talking about different species:
The fishes of the Fraser River include salmon and sturgeon.
Speaking about "two beer" and "two beers"—most languages have odd little local differences that can turn into dialects and eventually into distinct languages. Canadian usage permits "beer" as a plural; American usage, as far as I know, does not.
Linguists call the line between two such usages an "isogloss" (literally, "same language"). Just as an isobar on a weather map describes a region of equal air pressure, an isogloss describes a region where most people follow a particular usage or pronunciation. In the "beer" example, the isogloss runs right along the US-Canadian boundary.
Similarly, isoglosses separate British "lorry" and North American "truck," and Californian "fender bender" and Tennessee "car smash" (a usage that scared me when I had to drive on the icy streets of Memphis long ago, and the papers warned of smashes galore).
I suspect isoglosses also exist between social classes and generations. My generation uses "said" for "said." My students use "like":
"So Crawford is like, 'We have a quiz on Monday,' and I'm like, 'Omigod, I can't be there!"