Cat Goes Fishing Wikia
"The Garder patrol the coral reef. They tend to bite the bite before it can reach more valuable fish."

Garder fish in a video of how to catch it on youtube

garder fish are small, and a fully intact one can be sold for $2,200, or it may be casted out for medium bait. garder fish are brown and small, hiding in the caverns or amongst other fish in the reef, and will bite the bait before it can go any further, which is annoying when you're aiming for others. They tend to see the bait before the other fish do, and chase it down and bite on. Garders are not specifically attracted to any time, but come out any part of the day or night.