Hi! So this is a simple guide that will help you find the fishing cat achievement by giving you incremental hints and spoilers on how to find it. This cat is bonus and does not count in the 100 cats.

1. The cat's name is Schrödinger and is in fact linked to the fishing rod near the gas station.

2. The cat is ONLY visible from a specific area nearby.

3. The cat is not microscopic and is of normal size. It appears and disappears depending on what you are looking through.

4. You can't see it if you stay near the fishing rod. Try going a little farther.

LAST HINT (This will reveal the location)
5. You have to look at the fishing rod through the fence that is located nearest the fishing rod on the small dock. Try going to the bus stop near the gas station while still looking at the dock. Once aligned, you will see a cat fishing. You can always see this cat when the fence is aligned. Only this fence works.

I hope this helped you find the fishing cat and that you got the achievement!