A bottom feeder can be kosher. Bottom feeding is about where a fish eats, not about fins and scales, so it does not decide kosher status on its own.
The common mix-up
People often assume “bottom feeder” means “not kosher.” It does not. The only test is fins and scales. A bottom-dwelling fish with true fins and removable scales is kosher, and plenty of them are.
Where the confusion comes from
Some well-known non-kosher fish, like catfish, do live and feed on the bottom. But they fail because they have no scales, not because of where they feed. Other bottom dwellers have proper scales and pass without issue.
How KosherFish handles it
When a fish is a notable bottom feeder, the description mentions it for context. The kosher verdict still rests only on the fins-and-scales checklist. So read the checklist, not the feeding habit, to know the answer.