Both should be accepted. In English you can't count garlic without the word "clove" but in Romanian you can count garlic without any extra word or you can also use the Romanian word for "clove" which is indeed "cățel".
No, it's not. There are a very few technical contexts where one might use "fishes". Even then "kinds/species of fish" would be more natural. In most cases only "fish" would be correct for the plural of "fish".