Moss. Mud fish, also known as brown basket fish, has a special smell of algae eating fish in its abdomen. It is a herbivorous fish in the ocean, most afraid of moss. Moss is a general term for some filamentous green algae, which is common in fish fry ponds. Float on the water like a green net when it is prosperous, and it is yellow-green cotton wool when it is aging. Fish fry are not only easily entangled to death when they get in, but also absorb a lot of nutrients in the water, making the water dilute.