Animal names and collective nouns - patterns?
I probably learned this in fourth-grade science, but forgot and it's been bugging me lately so now I'll bug you all.
Why is it that for certain kinds of animals we have so many collective nouns in English that are the same as singular: that is, the singular and the plural forms are the same? Examples: sheep, elk, moose, etc; and perch, goldfish, trout, salmon, haddock, cod, etc. Is it a special ruminant-fish thing, did we get those groups of words from a single older language, or what is going on with this, if anything?