Lawnmower Blenny Care Guide | Diet, Habitat, Breeding, Tankmates

Jul 18, 2022

Lawnmower Blenny

Image Credit: Denis Cheong (CC License)

Lawnmower blenny is one of the first marine fish I kept as a beginner hobbyist. It was back in 2010 – I kept 4 lawnmower blennies in a 110-gallon tank. Oh boy, was it fun!

These saltwater fish are cute, curious, and animated. As the fish observe you whimsically with their orbital eyes, they look exactly like miniature chameleons. 

The appearance isn’t the only similarity they have with color-changing reptiles. As a matter of fact, lawnmower blennies are so aware of their surroundings that they can change the color and its intensity based on their environment or mood. 

If you have a marine or reef setup, a lawnmower blenny can be an excellent addition to your tank. As the name suggests, they graze on algae all day long – keeping your tank clean and pristine at all times.

This lawnmower blenny care guide will give you a rundown of everything you need to know about raising these fascinating creatures. 

So without any further ado, let’s begin! 

Lawnmower Blenny At A Glance 

  • Name: Lawnmower Blenny
  • Other Names: Rock Blenny, Jeweled Rockskipper, Sailfin Algae Blenny
  • Scientific Names: Salarias fasciatus
  • Family: Blenniidae
  • Size: 4-5 inches (10-13 cms)
  • Lifespan: 4 years
  • Care Level: Easy or moderate 
  • Temperament: Semi-aggressive 
  • Diet: Detritivore 
  • Tank Size: 40 gallons
  • Temperature: 72-78 degrees F
  • pH: 8.1-8.4

Lawnmower Blenny Introduction And Origin 

Lawnmower blenny comes from Blenniidae family. 

First discovered in 1786 by Bloch, it was named Salarias fasciatus. 

They’re one of the 13 species in the genus Salarias. They come from the Blenniidae family, including all combtooth blennies. 

The fish is native to the Indian Ocean off the East African Coast, Great Barrier Reef, Samoa, Red Sea, and the Islands of Micronesia. 

These fish inhabit shallow reef flats and lagoons with very heavy algae cover, sponges, stony corals, and coral rubbles. They are found at depths of 260 feet. 

Lawnmower Blenny Lifespan

A Lawnmower blenny’s average lifespan is 4 years. However, in the tank, its lifespan depends upon several factors, such as diet and water conditions. 

Lawnmower Blenny Price 

Lawnmower blennies cost between $20 to $40 based on your location and the fish’s size. Since they are one of the most popular types of blennies out there, it’s not difficult to find a stock near you. 

Whenever you’re buying any livestock, make sure to carefully observe for signs of disease. If anything about the fish looks off to you, don’t buy the fish.

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Lawnmower Blenny Appearance 

Lawnmower blennies make a great addition to any marine setup. They have a distinctive appearance that will certainly turn a few heads and start conversations. 

The feature that stands out the most to me is the large orbital eyes on each side of the rather blunt head. Since the eyes face outwards, they can move independently – allowing these fish to have a large field of vision.

The black pupils have white stripes extending from them. A series of teal dots surrounds each eye. These scattered dots are also present on the face.

The body doesn’t feature many colors but has an interesting pattern. The body has a striped/banded pattern in green, tan, gray, and brown colors. 

They have a single dorsal fin with the same design that runs across the entire body length. 

The earthy colors and patterns allow them to blend in easily against rocks and corals. They’re hard to spot at first glance if you’re not paying attention. 

They also have highly flexible jaws and comb-like teeth, making it easy to scrape food from hard surfaces like corals. 

The lips are big, and they have cirri on their heads. The body is long and slender. 

Lawnmower Blenny Size | How Big Do Lawnmower Blennies Get?

Lawnmower blenny doesn’t grow too big. They reach 4-5 inches (10-13 cm) in length. In captivity, the growth rate depends upon factors like diet and water conditions. 

Lawnmower Blenny Male VS Female

The sexual dimorphism in lawnmower blennies is as subtle as it comes. Males and females look almost identical. 

The main differentiating factor is that females are often a bit rounder and larger. Also, males possess elongated anterior rays on their anal fin. 

Lawnmower Blenny Behavior 

Lawnmower blennies have a friendly, curious, and outgoing personality. These fish are pretty aware of their surroundings and will even ‘greet’ you if you get close to the tank. 

They are believed to recognize regular faces – and thus may reward you with a few theatrics every once in a while. Their large, protruding eyes will follow you if you’re nearby. 

They are solitary creatures that spend most of the time alone at the base sitting still or quietly exploring. 

Although lawnmower blennies are peaceful for the most part, they can lose their temper every once in a while. They can be quite aggressive towards lagoon species like seahorses and pipefish. 

They may occasionally pick up a fight with congeners, conspecifics, or other fish of the same species. They’re also known to nip at polyps and other tankmates if they get too close for comfort. 

If they harass other gentle creatures in the tank, be prepared to relocate them. They often try to eat algae films off of the scales of different creatures in the tank. 

Hobbyists report that these fish can be quite stubborn. It’s hard to remove them from a rock if you are trying to move the fish. A fish trap might be helpful in this case. 

They usually stay still but will hop between rocks every now and then to find food. That’s why they’re also monikered Rock Skipper. 

Aggression isn’t really that big of an issue if you’ve carefully selected the right tank mates. In the right environment, they make excellent community fish. 

That being said, in my experience, these fish do get a little mean and aggressive as they age. They especially become hostile towards their own kind or other closely related species. 

Lastly, even though algae is their preferred food choice, they’re known to nip at clams and SPS coral polyps. So, be careful!

Lawnmower Blenny Tank Mates

Lawnmower blennies aren’t downright mean, but they can hold their ground in a community tank against most fish. So, finding tankmates for these chameleon lookalikes isn’t terribly hard. 

Most peaceful reef species make excellent tank mates. However, lagoon species like pipefish might struggle. Blennies try to eat algae film off of their scales. 

Unfortunately, lawnmower blennies aren’t considered to be reef safe since they routinely nip at coral polyps and can possibly lead to a lot of damage.

Invertebrates make great tank mates and are quite safe since they will be ignored by the lawnmower blenny. 

So, you can add crabs, snails, and shrimps to a lawnmower blenny tank. 

Bad Tankmates For Lawnmower Blenny

As discussed above, lawnmower blennies are generally peaceful and tolerant when kept with other community fish. But here’s a catch – keeping more than one blenny or any other fish that eats algae or remotely looks like blenny is to be avoided. 

Here’s a list of fish to avoid keeping in a lawnmower blenny tank:

  • Angels 
  • Anglers 
  • Damselfish 
  • Frogfish
  • Groupers 
  • Lionfish
  • Large dottybacks 
  • Pipefish 
  • Sea horses 
  • Triggers 
  • Toadfish 

Can You Keep Multiple Lawnmower Blennies Together?

Lawnmower blennies do not prefer the company of their own kind. Keeping more than one blenny together in the same tank will most likely lead to serious squabbles and injuries. 

The fish resort to aggression to protect their territory and resources. 

If you want to keep more than one blenny, you’ll require a tank of at least 100 gallons or bigger. 

If you want to breed these fish, you can keep a mated pair in a tank with plenty of hiding spaces. 

Lawnmower Blenny Diet | What Does A Lawnmower Blenny Eat?

There’s a common misconception about a lawnmower blenny’s diet. Due to their propensity to consume algae growing on any surface, they’re thought to be herbivores. 

However, they are principally detritivores, feeding on dead and decomposing organic matter. Studies have shown that plant material makes up only 15% of their diet in the wild. 

They will eat filamentous green microalgae, blue-green algae, hair algae, and detritus in the tank. The zest with which they will consume hair algae will differ from one fish to another.

Some will graze on it continuously like a lawnmower, whereas others will try it, discard it, and instead eat prepared food. 

They will also eat small invertebrates, sponges, eggs, and small snails if available. 

In captivity, algae make up the main source of their diet. Therefore, lawnmower blennies should only be kept in established tanks that already have algae films. 

You can give store-bought algae wafers and pellets if you think the algae growing in your tank is insufficient. 

Occasionally, you can give fresh vegetables like lettuce, cucumber, zucchini, and spinach. 

Nori is another vital marine algae supplement that you can add to the fish’s diet. Also, always have some processed fish food in stock for emergencies. 

If you plan to regularly feed processed fish food, you must introduce them to the fish when it’s young. Adults take a very long time to acquire a taste for new food, and that is if they do at all.

If the fish declines to eat new food, you’ll have to sustain them on just algae, which can be trickier if you’re a beginner in the hobby. 

Remember not to overfeed and remove the uneaten food before it decays. Pay special attention if there’s no cleaner fish in the tank.

Uneaten food will pollute the water, and polluted water will make the fish susceptible to a number of health conditions like ich. 

If possible, add a couple of cleaner fish in the blenny tank so that they get rid of the uneaten food and gunk right away. 

While feeding, you need to be careful with the tank lid as these fish have a knack for jumping quite high. Also, the fish will claw at corals and nip clams if famished. 

Recommended Lawnmower Blenny Food (Frozen):

  • Emerald Entree 
  • Reef Nutrition Formula Two
  • Hikari Mega Marine 

Recommended Lawnmower Blenny Food (Dry):

  • Seaweed Extreme Pellets
  • ZooMed Spirulina Flakes 
  • Reef Nutrition Formula Two Pellets 
  • Algae Wafers 

How To Acclimate Lawnmower Blenny To Prepared Foods?

To acclimate lawnmower blenny to prepared food, you need to start experimenting when they’re young. They’re too stubborn to change their palate once they’re old enough. 

Start out by feeding small amounts when you believe they’re actually hungry. 

A possibility you need to consider is that a wild-caught specimen can never acquire a taste for prepared aquarium food. In that case, you must ensure they get all the required nutrients from naturally-occurring algae in the tank. 

Can Lawnmower Blenny Eat Mysis Shrimp And Brine Shrimp?

Speaking from my experience, yes, lawnmower blenny will eat mysis shrimp and brine shrimp if they like their taste. 

However, remember that these meaty foods are meant for carnivores and omnivores. Therefore, they may not be nutritionally whole enough to meet the diet requirements of detritivores. 

Lawnmower Blenny And Starvation

Unfortunately, lawnmower blenny has a long track record of starving in the home aquarium. So you need to keep an eye out to make sure that they are eating well. 

If they are, you can notice active rasping of algae from the surface and that they have filled and thus rounded bellies. If they are starving, they will lose muscle tissue starting behind the skull along their dorsal region. 

Lawnmower blennies need a large surface area to graze on and a constant supply of algae – especially when they haven’t learned to take prepared foods. 

If you keep lawnmower blennies in a tank that doesn’t have enough algae, they will starve and die before they figure out the food you’ve been offering is edible too. 

They’re notoriously fussy about what they put in their mouth and require algae/vegetable content in their every diet. 

One hobbyist reported that when his blennies were starving, he tried a dozen different foods in a quest to get them to feed. He had success with the following two products:

  • Algae wafers 
  • Seaweed Extreme

How Often To Feed A Lawnmower Blenny?

Lawnmower blenny should be given supplemental food once daily, provided that there’s a food source already available in the tank. 

These fish are true to their name. In the tank, you’ll find them constantly grazing on the algae. If there’s ample algae available to begin with, you can channel moderation while offering supplemental food.

Lawnmower Blenny Tank Setup 

It’s wise to consider a fish’s natural habitat when designing a habitat for it. As much as possible, we must try to emulate the natural conditions of their native habitat. 

In this section, I will walk you through everything you need to know about creating an ideal habitat for lawnmower blenny and ensuring its wellbeing. 

Recommended Tank Size For Lawnmower Blenny 

The minimum recommended tank size for a single lawnmower blenny is 40 gallons. The tank’s dimensions should be something like this: 48″ x12″ x16″. 

Of course, the bigger the tank, the better it is for the fish as there’s more surface area for algae growth, which by now you know is an essential dietary component. 

How Many Lawnmower Blennies Can Be Kept Per Gallon?

Although these fish don’t grow too big, keeping them together is not recommended since they’re intolerant of each other’s company. Therefore, you’ll need a considerably bigger tank if you plan to house multiple lawnmowers together. 

The rule of thumb is to provide an extra 30 gallons for each new blenny addition. 

Water Parameters For Lawnmower Blennies

  • Water Temperature: 72-78 degrees F
  • pH: 8.1-8.4
  • Salinity: 1.020=1.025
  • Hardness: 8-12 dGH
  • Nitrite: 0 PPM
  • Ammonia: 0 PPM
  • Flow Rate: Moderate-high

The water parameters should fall in the aforementioned range. As hardy as these fish are, they don’t react too well to sudden or drastic environmental changes.

Therefore, you must be careful when finetuning the parameters and maintaining the water quality. 

Once a week, test the ammonia, nitrite, nitrate, and phosphate levels with a reliable test to ensure nothing harmful is brewing in the tank. 

We use and recommend using API’s Saltwater Master Kit. I’ll leave the link below if you’re interested:

Also, routinely test the alkalinity and calcium levels to ensure they’re in the proper range. 

My weekly fishkeeping duties also include cleaning the glass panes using an algae magnet and wiping the neck of my protein skimmer. 

Based on the tank’s size and stocking number, regularly conduct water changes – at least once every two weeks. Remember that small but frequent water changes are more favorable than large but infrequent ones. 

A tip: Don’t replace the disposable mechanical filtration media the same day you change the water. Do it a couple of days before or after the water change. 

This will help preserve the good bacteria colony necessary for a safe and healthy aquarium. 

Since these fish require moderate to high flow, I recommend getting a proper canister filter with carbon filtration media and an air pump.

Substrate And Decoration For Lawnmower Blenny 

The substrate should be sandy for these bottom-dwellers. Since these fish are passionate about digging around to kill time, anything with rough or sharp edges will injure the fish. 

A tight-fitting lid is a must because lawnmower blennies love to jump high and might accidentally get out of the tank. 

To mimic their natural surroundings the best, add plenty of rock decorations. Position the rocks and decors so that there are plenty of hiding spots and open waters to swim around freely. 

Adding live plants is another easy and fun way to make them feel at home. 

For lighting, standard aquarium lighting will do fine – avoid bright lights. 

Breeding Lawnmower Blenny

I raised lawnmower blennies for around 5 years and was never successful enough to get them to breed. There aren’t many reports of these fish mating and producing offspring in captivity. 

For starters, getting your hands on a mating pair for breeding is incredibly hard. Telling males and females apart is next to impossible. 

Some people claim that males are a tad bit bigger than females, whereas others claim the opposite is true. Also, males supposedly have elongated anterior rays on their anal fins, lacking in females. 

Even if you have a guaranteed male and female in the tank, there’s no guarantee they will pair off and produce young ones. Blennies are known to be super picky about their breeding partner. 

If you want to stay optimistic, maintain a healthy environment to encourage the fish to breed. Keep the water clean and monitor the environment closely. 

Feeding a well-rounded and healthy diet is essential too. 

In the wild, these fish breed between April and June. The rising temperature and warmer water are some triggers to signal them to mate. 

So, in the tank, maintain the temperature around 78 degrees F. This will hopefully mimic their natural environment and stimulate them to breed. 

If they happen to breed, the female will lay fertilized eggs covered in a sticky substance so they can adhere to the chosen surface. 

In the wild, the eggs are often laid in empty shells. 

Once the female lays the eggs, the male is tasked to guard them against intruders. 

Therefore, it’s best to move the mated pair to a breeding tank if you think they’re going to make some babies. That being said, this may not be worth the effort since getting them to breed is quite rare. 

Lawnmower Blenny Diseases 

Lawnmower blennies are pretty hardy. However, if exposed to the wrong environment and fed the wrong diet for a prolonged period, they are susceptible to a slew of saltwater aquarium diseases like a parasitic infestation, ich, hole-in-the-head disease, and gas bubble disease. 

Parasitic Infestation 

Parasitic infestation happens most commonly when new fish are added to the main tank without proper quarantine. The stress of being transported and adjusting to a new environment causes the fish’s immunity to be compromised. 

And when the immune function is decreased, it allows any parasite riding along to quickly multiply and spread. 

Some common parasitic diseases blennies or any saltwater fish are susceptible to are: 

  • Marine ich
  • Brooklynella 
  • Marine velvet 

Some common clinical signs of parasites in saltwater fish are increased lethargy, labored breathing, bruises, loss of scale, and dark spots. 

The treatment differs depending on what’s troubling the fish. Don’t forget to seek professional advice and treat the fish accordingly. 

Bacterial Infection 

There are several bacteria species present in the tank at all times. A healthy fish’s immune system can keep them at bay most of the time. 

However, when the fish’s immunity is compromised, let’s say because of stress induced by poor water quality, aggression, or lack of food, they’re likely to develop a secondary bacterial infection. 

Some common signs of bacterial infection in marine fish like blennies are increased lethargy, suppressed appetite, and ulcers. 

Minor infections go away on their own once the primary stressor is identified and tackled. However, severe infections will require antibiotic treatment prescribed by the vet. 

Gas Bubble Disease

Gas bubble disease occurs when the water is supersaturated with pressurized gas, causing tiny bubbles to form in the fish’s skin and eyes.

This condition most commonly arises when there is misaligned plumbing sucking air into the filter tubing. As a result, you can see one big bubble or multiple bubbles forming in the fish’s skin and eyes. 

In any way, don’t try to pop the bubbles on your own. The vet will handle the ailment safely after anesthetizing the fish. 

Hole-In-The-Head Disease 

Hole-in-the-head disease, also known as lateral line erosion, cannot be traced to one specific cause. It could be due to the tank’s high nitrite and nitrate levels, poor water quality, malnourishment, and protozoan parasites. 

The case’s severity may range from a small spot on the head to the entirety of the face and side of the body experiencing skin erosion. 

Unfortunately, fish with severe cases may never return to their original appearance ever again. 

Frequently Asked Questions 

Are Lawnmower Blennies Hard To Keep?

If you’re a beginner, lawnmower blennies can be hard to keep due to their angry disposition, finicky eating behavior, and need for ample space. 

Growing algae in the tank without letting it overrun can also require some skill, experience, and elbow grease.

Do Lawnmower Blennies Jump?

Yes, lawnmower blennies jump – they often jump to death. Thus, it’s critical to have a tight-fitting lid always covering the tank. 

Final Words: Are Lawnmower Blennies The Right Fish For You?

As I just answered above, raising lawnmower blennies may not be a good idea if you’re testing waters in the saltwater arena for the first time. 

These fish require plenty of space and an endless supply of algae at all times. Thus, these factors can pose a challenge. 

Also, since they nibble on corals, they’re not reef-safe either. 

That being said, if you can house them with compatible tank mates in a big tank and meet their complex dietary requirements, raising lawnmower minnows can be quite a rewarding experience. 

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rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.