How do you you get the key out of the fish tank in Shrink ray island at poptropica?

To get the key out of the fish tank in Shrink Ray Island on Poptropica, you need to use the mini-shrink ray to shrink yourself down. Then, carefully navigate through the fish tank and avoid the fish while collecting the key. Once you've got the key, you can return to your normal size to proceed with your adventure.