Blenny Fish: The Lawn Mowers of The Ocean

By Hannah Henegarblenny1

Blenny Fish

Blennies are mostly small, usually marine fishes found from tropical to cold seas. They are slim, ranging in form from moderately elongated, as in some of the tropical species, to very long and eel-like. As a group, they are united by such features as a long dorsal fin and pelvic fins that are placed near the throat and contain one spine and two to four rays. Some blennies have scales and some do not; certain species have fleshy filaments on the head. Tropical Atlantic species include the striped blenny (found as far north as New York) and the more southerly freckled blenny. Those that live in kelp beds are mottled in coloration and those found in eelgrass are silver and green, matching their environment. The closely related wolf-fishes of the family Anarhichadidae, with large, tusklike teeth, are found in arctic Atlantic waters. They average 3 ft (90 cm) in length and are good food fishes, sold commercially as ocean catfish.

The habitats of blenny saltwater fish range from rocky pools to sandy beaches, reefs, and beds of kelp. Many live in shallow water, but some range to depths of about 1,500 feet. Blennies live on the sea bottom, among reefs, rocks, or kelp, in burrows or shells, or among eelgrass or algae in shallow brackish water; some species are found in freshwater. A number of species spend long periods out of water in moist tidal zones. Although many consume dead plant and animal matter, some species are mainly herbivorous, and others are partially to wholly carnivorous.They also feed on small invertebrates.  Blennies are generally bottom-dwelling fishes, except for the sabre-tooth clade (Aspidontus) that inhabits the water column. Many blenny species are also used as aquarium fishes.

The blenny is also known as a algae eating saltwater fish. Microalgae can cause great despair as it smothers their corals or makes a reef tank look like an overgrown meadow. This can be avoided by keeping phosphate and nitrate levels down, adding herbivorous invertebrates (snails and hermit crabs) to reduce algae and  algae-eating fish (tangs and rabbitfish, among others). Members of these two fish families can help control algal growth, but they are large and need a lot of swimming room.


The Lawnmower Blenny: Blue Lawn Mower

The Lawnmower Blenny lives in tropical parts of the Indo-Pacific. Its geographical range includes the Red Sea and the eastern coast of Africa and stretches eastward to Samoa and north to the Japanese Islands. Southwards, the Lawnmower Blenny can be found down to Australia’s Great Barrier Reef and New Caledonia.

The Lawnmower Blenny is primarily found on reef flats, seaward reefs, and in shallow lagoons. Estuarine environments where rubble patches of reef flats and slopes are covered in prolific algae growth are also appreciated by this species. The typical Lawnmower Blenny habitat consists of corals, rubble and/or sand. Lawnmower blennies stay fairly close to the surface where the sunlight is strong enough for rich algae growth and they are rarely encountered below 26 feet.

The Lawnmower Blenny is a rather drab looking creature. Just like most other blennies, it has an elongated body and the dorsal fin extends the length of the body. The fish is whitish and decorated with tan or gray bars and streaks along the sides. The head is blunt and the face is adorned with small light-blue and black dots. The eyes are located high up on the head. Around the face of the fish you can see elegant projections similar to delicate feathers. These tufts are known as cirri.

The Lawnmower Blenny derives its name from its remarkable ability to keep algae growth in the check in the aquarium and this has made it a popular aquarium inhabitant. The Lawnmower Blennies are mainly vegetarian and will feed by using its teeth to scrape algae off rocks and other surfaces in the aquarium. They are famous for eating hair algae, but are even fonder of film algae. Some specimens never touch hair algae.The Lawnmower Blenny  spends most of its time perched on rocks in the aquarium, when it is not grazing algae. The Lawnmower Blenny is considered reef safe, but it can nibble on stony corals.

These little guys are essential to saltwater life and can do some serious work on algae.