The Lawnmower Blenny is an algae-eating, herbivorous fish that eats filamentous green microalgae, diatoms, filamentous blue-green microalgae, and detritus. Please note the prefix 'micro' there--as it is meaningful. Microalgae include the films you see on glass and live rock, as well as the hair algae, which are just thin strands of essentially similar cells. The Lawnmower blenny diet is also known to include tiny invertebrates, eggs, sponges, and small snails, although not thought to be primary foods