Which fish form the plural by adding -s or -es?
Both herring and sardine, arguably
Yep, I'd say "herrings" and "sardines".
Trout plural is still trout... correct?
I think it's ridiculous that some species of fish are entitled to a distinct plural form but not others. This discrimination must stop before disaffected herring/herrings commit suicide.
I don't think you can pluralise any of those fish! It's all sheeps and mouses to me.
I think you'll find, Geoff, that wikipedia along with many other sources state that herring can be made plural by adding an 's'. Kind regards.
how can you add -es to sardine ???