The tailspot blenny is a small Indo-Pacific grazer with banded eyes, an amber body, and the namesake dark spot at the tail base.
It spends its day hopping between perches and mowing film algae.
It is among the best nano-reef fish: small, hardy, useful, and packed with personality for something the size of a finger.
Housing
A mature reef of 75 litres (20 gallons) or more with live rock suits it; maturity matters because natural algae and biofilm form the grazing base.
It claims a small hole or barnacle as home and returns to it constantly.
Reef-safe and coral-safe, it needs only standard stable parameters — 24-26C, salinity 1.024-1.026 — and, like most blennies, a tight lid.
Diet
Grazing alone rarely sustains one in a clean tank: offer nori on a clip several times a week plus spirulina-rich pellets or flakes.
It learns feeding routines fast.
A visibly hollow belly means it is losing the food race — feed more directly.
Mixed frozen foods are taken too, but vegetable matter should dominate.
Health
Tailspots are hardy and disease-resistant, with starvation in immature or over-clean tanks the main genuine risk.
Confirm feeding before purchase if possible.
Quarantine remains sensible.
Beyond that, watch only for jumping and for harassment by larger blennies or aggressive grazers competing for the same turf.
Temperament
Endlessly watchable: it perches on rockwork with curled tail, swivelling its banded eyes independently at everything that moves, then darts off to graze.
Many learn to recognise their keeper.
It is peaceful with everything except close competitors — keep one blenny in smaller tanks, as it may squabble with other algae-grazing blennies over territory.
It ignores corals, shrimp, and snails entirely.
A good fit for
Nano and small reef tanks needing personality
Keepers who want natural algae control
Peaceful communities of small reef fish
First-time marine keepers with mature tanks
Common mistakes to avoid
Brand-new tanks with nothing to graze
Starvation hiding behind 'it grazes all day'
Two grazing blennies fighting in small tanks
Open tops — blennies jump when startled
Is your enclosure big enough?
Minimum volume75 litres (20 US gallons)
CompanyMust be housed alone. One blenny per tank in smaller systems
In a reef, stability matters more than any single target number. A parameter moving fast does more damage than a parameter sitting slightly off.
Go now
Any detectable ammonia or nitriteWater change now with matched, mixed and aerated saltwater. Stop feeding. Directly toxic, and a marine system has less margin than a freshwater one.
Now
Temperature or salinity has moved sharplyCorrect slowly, over hours, not minutes. Check the heater and the top-off. The speed of the change does the damage. Correcting fast repeats the injury in the other direction.
Now
Rapid gilling, or a fish hanging in the flow breathing hardIncrease aeration and check temperature and salinity. Warm water holds less oxygen, and a heater failure shows up here first.
Now
Today
White spots, or a fine dusting like icing sugarIdentify which parasite before treating. Most reef tanks cannot be treated in place. The two common parasites look similar and need different handling; velvet can kill a tank in days.
Today
Corals closed for more than a day, or receding tissueTest alkalinity first, and compare it against the last reading rather than a target. Unstable alkalinity is the most commonly cited coral killer, and a swing shows up in the trend, never in a single point.
Today
A new fish added without quarantine now looks unwellRemove it to a separate system today if you can. Nearly every wipeout in a reef tank traces back to a skipped quarantine.
Today
Quarantine every new animal, including corals and inverts. It is the single practice that separates a reef that lasts from a reef that restarts.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Beginner
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