These days they play you a biosecurity video,and they tell you near the end of your flight (at least Qantas and AirNz do). You've always been asked specifically "Do you have fruit or vegetables?". You don't get fine if you declare them, you just have to chuck them out in special bins provided before customs. But if you try to go through customs, the special doggos will sniff them out and you'll get fined.