They all have plurals with "s" - melons, kiwi fruits, canteloupes, honeydew melons, pineapples.
With reference to your examples, you can say " I like pineapple" - the fruit [pineapple] in general; and "Take three pineapples" [specific].
"We need three kiwi fruits for this recipe." [specific] / "Kiwi fruit have a high vitamin C content." [general]
- For Teachers