Jewelled Blenny (Salarias fasciatus)

A grazing reef blenny for one settled marine aquarium

The Jewelled Blenny (Salarias fasciatus) is a combtooth blenny, family Blenniidae, from the shallow reefs of the Indo-Pacific. FishBase records it from the Red Sea and East Africa east to Samoa, north to the Ryukyu Islands and south to the Great Barrier Reef and New Caledonia, with a maximum of 14 cm total length. It lives close to the bottom, resting on rock and coral and scraping algae from hard surfaces, and it is also known as the lawnmower blenny and the algae blenny.

This is a fish for a keeper who already runs, or is ready to run, a mature marine aquarium and wants one interesting bottom-dweller rather than a shoal. It needs rockwork with algae already growing on it, stable marine water, room to claim a patch of its own and companions that are confident rather than shy.

Three figures that shape the plan

• Adult length: up to 14 cm total length, the FishBase maximum.
• Aquarium volume: at least 80 litres for one fish kept alone, and more with companions, following the OATA blenny care sheet, which names this species among the larger blennies.
• Water: 24–26°C, pH 7.9–8.3 and a specific gravity of 1.020–1.025, OATA's figures for blennies as a group rather than a species-specific optimum.

What arrives when you order

Each purchase supplies one live Jewelled Blenny. This product has one option, so there is nothing to pick beyond the quantity. The length of the fish on arrival and its adult length are different figures, and the aquarium, rockwork and companions should be planned around the 14 cm the species can reach rather than around the fish in the bag.

Sex is guaranteed only when the selected option explicitly states male or female. This Jewelled blenny listing has no sex-guaranteed option. Because OATA advises one blenny species per aquarium and this species can become territorial with age, the practical plan is a single fish, whatever its sex.

Gallery images have been digitally enhanced to improve image quality. Natural colour, pattern, size and maturity can vary between live animals. This matters more than usual with this blenny: it can change colour to blend with its surroundings, so the fish you unpack may look darker, paler or more mottled than the photograph.

If you are still choosing the rest of the stocking plan, compare candidates in our marine fish collection, then check each one against the companion guidance on this page before you add it.

Check your set-up before you order

A test kit and an honest look at your stocking list will tell you whether this blenny fits. Work through these points before you buy.

• Volume: 80 litres or more for the blenny alone, and larger with other fish.
• Maturity: an established filter, with ammonia and nitrite reading zero.
• Grazing: rock that already carries a film of algae rather than freshly scrubbed surfaces.
• Water: equipment that holds 24–26°C and a specific gravity of 1.020–1.025 steady from week to week.
• Food: nori sheets or another high-algae food ready for days when grazing runs short.
• Other blennies: no second blenny species, unless the aquarium is large with many visual barriers.
• Temperament: no shy fish that a territorial adult could pressure.
• Corals and clams: if you keep them, a commitment to keeping the blenny well fed.
• Delivery day: someone at home to receive the parcel and film the unboxing.

If every point is a yes, the care guidance below shows how to keep it that way. If one is a no, fix that first. A larger aquarium, a few more weeks of maturing or a different companion plan will do more for this fish over its life than any food or piece of equipment.

Build the aquarium around rock, grazing and space

Set the aquarium up as a piece of reef flat: solid rockwork with ledges to perch on, open patches of sand and rubble between the rocks, and enough flow and filtration to keep the water clean around every surface this fish grazes.

Start at 80 litres and size up for companions

OATA's advice is to buy an aquarium as large as possible within reason. Its sheet recommends at least 40 litres for an individual of the smaller blenny species and at least 80 litres for the larger ones, and it places this species in the larger group. Aquariums need to be larger again when blennies share them with other species, and a bigger volume gives steadier temperature and water quality.

• One Jewelled Blenny on its own: 80 litres as the minimum.
• With other fish: go larger than 80 litres, adding volume for every companion.

Recreate rock, sand and rubble

FishBase describes adults on reef flats, shallow lagoons and seaward reefs, usually among mixed coral, sand and rubble, and alone in weedy areas on rocks and coral outcrops. In the aquarium that means stable rockwork with flat tops and ledges for perching, and open sand or rubble between the outcrops. Blennies are relatively undemanding about décor, so the priority is plenty of hard surface for grazing rather than ornaments.

Filtration, flow and skimming

A filter is essential. In a marine set-up that can be live rock with sufficient water flow, an internal or external filter, or a sump-based system. A protein skimmer is also worth running, because it removes dissolved organic waste before it can break down into more harmful substances.

Mature the aquarium before it arrives

Fish release ammonia into the water, and ammonia is toxic. The RSPCA's aquarium guidance explains that a working biological filter grows beneficial bacteria that convert ammonia into nitrite, which is also toxic, and then into nitrate, which is safer. No fish should be kept without a well set-up and maintained filter, and this blenny needs that bacterial population fully established before it goes in.

Why a young aquarium is risky

OATA explains that the bacteria in a matured filter have to increase every time more fish are added and feeding increases. Overstocking, or stocking too quickly, leads to new tank syndrome: there are not enough nitrifying bacteria to cope with the extra waste, ammonia and nitrite climb, and fish can become ill or die. A grazer that also depends on algae growing on the rock is doubly poorly served by an aquarium that has only just been set up.

Signs the aquarium is ready

• Ammonia and nitrite read zero on repeated tests, with some nitrate present.
• A film of algae has grown over the rockwork.
• Temperature, pH and salinity have held steady within the ranges in the water section.
• Any fish already in the aquarium are feeding and behaving normally.

Let algae grow before the fish arrives

This blenny spends its day scraping hard surfaces, so it should go into an aquarium where the rock has already grown a film of algae. A newly scrubbed or freshly set-up aquarium leaves it with little to graze and raises the risk of the ammonia and nitrite spikes that stress blennies.

Plan for the 14 cm adult

FishBase gives 14 cm as the maximum total length for this species, measured from the snout to the tip of the tail. That is the figure to plan around, whatever the length of the fish when it arrives.

What changes as it grows

• Space: OATA's figure of at least 80 litres for larger blennies applies from the start, because the aquarium has to suit the adult.
• Territory: OATA notes that this species can become quite territorial as it grows older, so a companion that is left alone by a small blenny can come under pressure later.
• Food: portions grow with the fish, but the rule stays the same: only what it clears within a few minutes.
• Waste: a larger fish adds more to the filter's workload, so the weekly routine matters more each year.

Why the arrival length is the wrong guide

Choosing an aquarium or companions around the fish in the bag tends to work for a while and then fail, just as the blenny becomes more territorial. OATA also notes that blennies can live for many years in a well-matured set-up with good water quality, so the aquarium you choose now needs to suit a full-grown fish for most of its life.

Keep marine water steady and within range

Keep the aquarium at 24–26°C, pH 7.9–8.3 and a specific gravity of 1.020–1.025, with ammonia and nitrite at zero. These are OATA's suggested values for blennies, which it describes as usually undemanding of water chemistry. Aim to hold them steady from week to week.

Reef aquariums

OATA points out that some of these values will need to be altered in a reef aquarium to accommodate more sensitive species. If you keep corals or other delicate invertebrates, set the aquarium for them and make any adjustment gradually, keeping the blenny's temperature, pH and salinity within the ranges above.

Estuary records do not mean brackish water at home

FishBase lists the species as marine and brackish, recorded in estuarine areas with algae-rich rubble as well as on reefs, from the intertidal zone down to about 8 metres. That describes where wild fish have been found, not a recommendation to lower salinity at home: keep this blenny in full marine water at the specific gravity shown in the table.

If a reading drifts

• Ammonia or nitrite above zero: add no more livestock, check the filter for blockages and look for uneaten food breaking down in the rockwork.
• Nitrate heading towards 50 mg per litre: review feeding amounts and keep up the weekly water changes described below.
• Temperature or salinity outside range: bring it back into range gradually and retest.

Feed a grazer: algae first, extras second

FishBase describes the Jewelled Blenny feeding by scraping algae off hard surfaces. The Wikipedia species summary adds an important detail: despite the lawnmower nickname, it is principally a detritivore, and plant material makes up only about 15% of its diet. In practice it works over the film of algae and fine organic matter that coats the rock.

Build the menu

• Grazing in the aquarium: algae growing on the rockwork is the foundation, so keep some surfaces unscrubbed.
• High-algae foods: OATA recommends foods with a high algae content, such as nori algae sheets, for herbivorous blennies alongside grazing.
• Small frozen extras: OATA notes that omnivorous blennies also appreciate small frozen meaty items such as mysis shrimp, enriched brine shrimp or copepods. Offer these in modest amounts and watch whether your fish takes them.

How much and how often

OATA's rule is to feed blennies only what they can eat within a few minutes, twice a day. Take care not to overfeed: uneaten food breaks down and releases toxic waste into the water, which this fish tolerates poorly. If food is still lying on the rock after a few minutes, reduce the next portion.

When grazing runs short

If the rock starts to look scraped bare, the blenny is taking more than grows back. Increase the high-algae foods rather than the frozen extras, and leave more rock surfaces unscrubbed during maintenance, while still feeding only what it clears within a few minutes.

Signs the diet is working

• Its body weight and condition stay steady from week to week.
• It moves between perches and grazes steadily through the day.
• It shows interest when food arrives instead of ignoring it.

A well-fed blenny also matters in a reef, because some blennies nibble corals or clams when underfed. Do not rely on this fish to clear an algae problem on its own; nuisance growth still needs its causes, such as overfeeding and skipped maintenance, dealt with directly.

Arrival day: from sealed parcel to rockwork

Our team hand-bags each fish in pure oxygen and packs it in an insulated poly box, with a heat pack when the weather calls for it. We email the tracking number and your confirmed delivery date, and a licensed live-animal courier carries the parcel. Someone needs to be at the delivery address to receive it, because live fish cannot be left unattended. The full terms are on our delivery and Live Arrival Guarantee page.

Steps on the day

1. Be at the delivery address to receive the parcel.
2. Start a continuous unboxing video while the parcel is still sealed, with the outer box in view. Film every delivery this way.
3. Keep filming in one take as you open the box the same day it arrives, until the fish can be seen still inside the sealed bag.
4. Float the sealed bag in the aquarium for 20–30 minutes to acclimatise the fish slowly.
5. Release the blenny into the aquarium without pouring the bag water into your tank.
6. If anything has gone wrong, contact us the same day, WhatsApp being fastest, with your order number and the unboxing video, and we will arrange a replacement or refund.

Check the aquarium before the fish goes in

OATA's introduction advice is to confirm that the aquarium is the right size for the blenny and that ammonia and nitrite both read zero before it goes in. Test the day before delivery, so there is time to act if a reading is off, and have the heater and filter running normally.

The first week

• Expect it to explore the rockwork and settle on favourite perches.
• Look for the signs OATA gives of a healthy fish: clear, bright eyes, undamaged fins, intact scales, no ulcers or bumps, and normal swimming.
• Start with small portions and increase only once it is grazing and feeding reliably.
• Hold back any further additions to the aquarium until your tests stay at zero ammonia and nitrite.

Weekly upkeep that keeps a blenny thriving

Good husbandry is what keeps a blenny healthy. OATA stresses that blennies can be stressed by even the smallest amounts of ammonia and nitrite, which may then lead to various diseases, so the routine below is about catching waste before it builds up.

Water changes

At least once every week, a partial water change of 25% is strongly recommended. Use a siphon to lift solid waste from the sand as you go, paying attention to the gaps between rocks where food and detritus collect.

Filter and skimmer care

Check filters regularly and clean them to prevent blockages. Do not run filter media under the tap, because chlorine or chloramine in tap water may kill the beneficial bacteria living in it. Rinse media lightly in the aquarium water you have just removed during the water change, which keeps more of those bacteria alive. Clean the protein skimmer regularly so it keeps working at full performance.

Testing

Test ammonia, nitrite and nitrate together with pH, and compare each result with the table in the water section. A log of weekly readings makes gradual drift easy to spot before the fish reacts to it.

Worked example: an 80-litre aquarium

In an 80-litre aquarium, a 25% change means replacing 20 litres each week. Prepare the replacement salt water so its temperature and specific gravity match the aquarium's own readings, siphon the 20 litres out from the sand and the gaps between rocks, rinse any clogged media in that removed water, then refill slowly. Matching the new water keeps the change from pushing readings outside the ranges in the water table.

A simple weekly checklist

• Change 25% of the water and siphon debris from the sand.
• Rinse any clogged media in removed aquarium water, never under the tap.
• Clean the protein skimmer.
• Test and record ammonia, nitrite, nitrate and pH.
• Leave some rock surfaces unscrubbed so grazing continues.

Spot problems early and act on them

Every fish varies a little in behaviour and appearance, so the useful skill is noticing change. OATA lists the changes worth watching for; here is how each applies to a rock-dwelling blenny.

• Swimming: hanging at the surface, sitting on the bottom or erratic swimming. This blenny naturally rests on rock, so judge resting against its usual routine and look for a fish that stops moving between perches.
• Colour: turning darker or paler than normal. This species changes colour to blend with its surroundings, so read a colour shift together with the other signs rather than on its own.
• Temperament: becoming more aggressive or hiding more than normal.
• Breathing: gill covers moving faster or slower than usual.
• Appearance: white spots, fluffy growths, or loss of fins or scales.
• Condition: an increase or decrease in body weight.
• Feeding: eating less, or showing no interest in food.

What to do next

1. Test ammonia, nitrite, nitrate and pH straight away.
2. Correct any reading outside the water table before changing anything else.
3. Note what has changed and when, including feeding and any new additions.
4. Contact us with your results so we can help you work out the next step.

Keep a simple record

OATA's point is that noticing changes early helps identify problems before they become a real health issue. A short weekly note of test results, how eagerly the blenny feeds, which perches it uses and its usual colouring gives you a baseline to compare against. When something looks different, that note tells you whether it is new.

Because even small amounts of ammonia and nitrite can stress blennies into disease, the testing routine comes first whenever something looks wrong.

How it lives in the wild, and what that means at home

Knowing how the species lives in nature explains most of its aquarium needs.

Habitat and breathing

FishBase records the species from the intertidal zone to a few metres deep and describes it as a facultative air-breather, able to take in air as well as breathe through its gills. It also notes that the fish has neither a fang nor a venom gland. Its IUCN status is Least Concern.

Camouflage

The species blends with its surroundings and can change colour to hide from predators. That is one reason the spotted, banded pattern of a fish in the aquarium may not match a photograph exactly.

Breeding biology

The Jewelled Blenny lays eggs. They are demersal and adhesive, attached to the substrate by a filamentous, adhesive pad or pedestal, and the larvae that hatch are planktonic, often found in shallow coastal waters. With one fish per aquarium and no guaranteed sex, this is a species to keep for its behaviour rather than to breed.

Choose companions around its territory

Most blenny species mix well with other fish, but this one comes with a clear warning. OATA singles out the algae blenny, another name for this species, as able to become quite territorial as it grows older, and says it should not be mixed with shy species. Build the community with that adult behaviour in mind from the start.

One blenny per aquarium

Keep a single Jewelled Blenny. FishBase describes wild fish as solitary, and OATA advises no more than one blenny species in an aquarium unless the aquarium is large with many visual barriers, because blennies may become territorial with one another.

Companion guidance

OATA reminds keepers to consult their retailer before buying any blenny, to make sure it will mix with the fish already in the aquarium. Ask us with a list of your current stock and aquarium volume, and we will talk it through with you.

Build the community in a sensible order

OATA's wider advice is that aquariums need to be larger when blennies share them with other species, and that fish numbers should rise slowly. These steps turn that into a plan for this blenny.

1. Write down every fish and invertebrate you keep or intend to keep, with the aquarium's volume.
2. Take shy species out of the plan, or choose a different fish instead of this blenny.
3. Check that no other blenny species is present unless the aquarium is large with many visual barriers.
4. Mark firefish, shrimp gobies and other similar-looking bottom-dwellers for close watching.
5. Add livestock gradually, so the filter bacteria keep pace with the extra waste.
6. Test ammonia and nitrite after each addition, and pause if either rises above zero.

Reading territorial trouble

OATA's list of warning signs includes a change in the level of aggression and hiding more than normal. Apply it to both sides. A blenny that starts chasing others away from its rock, or a companion that stops coming out to feed, both mean the arrangement needs rethinking. More rockwork, a larger aquarium or rehoming one of the fish are the practical fixes.

Give each bottom-dweller its own patch

Because this fish claims rock as it matures, spread perches and ledges across the aquarium rather than building one central pile. Separate outcrops give other bottom-living fish somewhere to settle out of the blenny's direct view.

Corals, clams and reef aquariums

A reef aquarium can work for this blenny, but plan for two things: water that suits the most sensitive animals present, and a fish that never goes hungry.

Why feeding decides reef safety

OATA notes that some blenny species may nibble corals or clams, particularly if underfed. A grazer that finds too little algae and too little food on the rock is more likely to test other surfaces. Keep algae growing, feed the high-algae foods described in the feeding section, and watch the fish around any coral or clam you value.

Practical reef checks

• Before adding the blenny, make sure the rockwork carries a healthy film of algae.
• In the first weeks, watch where it grazes and whether it picks at coral tissue or clam mantles.
• If it does, increase grazing opportunities and review portion sizes before anything else.
• Adjust reef water values gradually for the corals, keeping temperature, pH and salinity within the blenny's ranges.

A fish-only aquarium with plenty of live rock avoids the coral question entirely and still gives this species everything it needs: surfaces to graze, perches to hold and stable water.

Questions keepers ask before buying

How big does a Jewelled Blenny get?

FishBase records a maximum of 14 cm total length for this species. Whatever its length on arrival, plan the aquarium, the rockwork and any companions around a 14 cm adult rather than the fish in the bag.

What size aquarium does it need?

OATA's blenny care sheet recommends at least 80 litres for the larger blennies, and it names this species among them. Treat 80 litres as the starting point for one fish kept on its own; the aquarium will need to be larger if you want to keep it with other species.

How many Salarias fasciatus should I keep together?

Keep one. FishBase describes wild fish as solitary on weedy rocks and coral outcrops, and OATA advises keeping no more than one blenny species in an aquarium unless it is large with many visual barriers, because blennies may become territorial with one another.

Is this blenny suitable for beginners?

Its needs are clear rather than exotic. OATA describes blennies as usually undemanding of water chemistry, but they can be stressed by even the smallest amounts of ammonia and nitrite, so it suits a keeper whose aquarium is mature, tested regularly and already growing algae on its rock before this fish goes in.

What does a Jewelled Blenny eat?

In the wild it scrapes algae from rock, and much of what it takes in is detritus rather than plant material. Let it graze algae growing in the aquarium, add high-algae foods such as nori sheets, and offer small frozen foods such as mysis shrimp as extras. OATA advises feeding only what it can eat within a few minutes, twice a day.

What temperature and pH does it need?

OATA's blenny guidance gives 24–26°C, pH 7.9–8.3, a specific gravity of 1.020–1.025 and carbonate hardness of 8–12 dKH, with ammonia and nitrite at zero and nitrate no higher than 50 mg per litre. These figures cover blennies as a group, so hold them steady rather than chasing a precise number.

Is the Jewelled Blenny aggressive?

It feeds by grazing rather than hunting, but OATA warns that the algae blenny, as this species is also called, can become quite territorial as it grows older. Keep it away from shy fish and watch it closely with similar-looking bottom-dwellers such as firefish or shrimp gobies.

Which fish and invertebrates can it live with?

Most blennies mix well with other fish species, so confident marine fish that are not shy are the kinds to consider. Avoid a second blenny species in an average-sized aquarium, and in a reef keep it well fed, because some blennies nibble corals or clams, particularly when underfed.

How does it arrive alive in the UK?

Your Jewelled Blenny is hand-bagged in pure oxygen inside an insulated poly box, with a heat pack when the weather calls for it, and carried by a licensed live-animal courier with tracking. Be in to receive it, start filming while the parcel is still sealed, open it the same day in one continuous take, float the bag for 20–30 minutes and release the fish without the bag water. For a Live Arrival Guarantee claim, send the unboxing video and your order number the same day.

References

• FishBase: Salarias fasciatus. Identity, family, distribution, wild habitat, feeding mode, breeding biology and maximum recorded length.
• Wikipedia: Salarias fasciatus. Common names, detritivore diet and colour-changing camouflage.
• OATA: How to look after blennies. Group-level water values, aquarium size, feeding, maintenance, health checks and compatibility for blennies.
• RSPCA: fish environment guidance. Filtration and the nitrogen cycle for any aquarium.