This basically means you have accumulated 9000 fish in your foodbank. You get a fish in your foodbank when you eat a fish (duh). Eat 9000 of them and this achievement will be yours. 9000. That's a lot. You wont be able to get this simply through one playthrough of timed mode and adventure mode. Therefore, if you're a diehard fan, you'll need to replay levels.
1) Combine this achievement with 10 Hours, the 40,000 food bank achievement, and Shark Eater.
2) You can do one of two things. You can either just keep replaying through the game or you can keep replaying certain levels. I recommend altering between the two to make it less repetitive.
3) Start by working towards "Shark Eater" by replaying a level with Sharks in it. I recommend one that has "Mines" in it so that you can kill yourself before you beat the level so you can eat some more sharks with your plentiful lives. Level 37 is a good level to do this on. NOTE: YOU MUST BEAT THE LEVEL TO HAVE THE SHARKS COUNT TOWARDS THE ACHIEVEMENT. DO NOT LOSE ALL YOUR LIVES BEFORE BEATING THE LEVEL.
4) You don't get points in your foodbank while playing Time attack mode, so make sure you're in adventure mode.
5) I've heard a lot of people recommending level 21. I've heard reports of people getting up to 800 fish added to the foodbank before completiting this level with their last life.