The plural forms of “fish” and “fruit”

During my visit to one of the schools this morning,┬áthere was an argument about the plural forms of “fish” and “fruit”. A teacher was determined that these two words are uncountable and have no plural forms. I told the teacher that the plural forms could be (fish – fihes) / (fruit – fruits). When these words are used as collective nouns, the plural forms are: fish/ fruit, but if used to refer to different kinds of fish or fruit, the plural forms become: fishes and fruits. The following link gives more information about Plural forms of nouns. You can also visit the following link to see a Guide to Forming Plurals.
The lesson we learn from this argument is that we have to give ourselves time to look for the accurate information before we feel confident about a certain topic.