Saltwater Fish

Midas Blenny

Ecsenius midas

Golden, eel-like swimmer with bold charm · Beginner

Lifespan: 4-6 years
Adult size: 10-13cm (4-5in)
Min. habitat: Aquarium 110L+ / 30gal+
Social needs: One per tank unless a bonded pair
Diet: Omnivore, zooplankton and algae
Time: Low
Cost: Medium

Overview

The Midas Blenny is a golden-yellow fish with bright eyes and a graceful, eel-like swimming style unusual among blennies.
Hardy and personable, it is a good beginner marine fish that often hovers in open water rather than perching.

Unlike many blennies it is a midwater feeder that associates with the anthias it naturally schools with.
It can shift colour from gold to bluish depending on mood and surroundings.

Housing

Provide a reef tank of at least 110L (30 gallons) with live rock offering caves and crevices it can dart into and claim.
It favours a hole or tube as a base from which it watches the tank.

Maintain temperature 24-27C (75-81F), salinity 1.024-1.026, pH 8.1-8.4, and ammonia and nitrite at zero.
A secure rockwork retreat makes for a confident, frequently visible fish.

Diet

An omnivore that feeds largely on zooplankton in the water column, supplemented by some algae.
Offer frozen mysis and brine shrimp, marine flakes and pellets, and algae-based foods one to two times daily.

It readily accepts prepared foods and is an enthusiastic feeder, making it easy to keep well-nourished.
A varied diet maintains its golden colour and active behaviour.

Health

Hardy and adaptable, with fewer disease problems than many marine fish, though quarantine is still wise.
Stable water and a varied diet keep it healthy and brightly coloured for years.

Watch for hiding, faded colour, or refusal to eat as early warning signs.
Most issues arise from poor water quality, aggressive tankmates, or an immature tank rather than inherent fragility.

Temperament

Peaceful toward most species but territorial toward other blennies and sometimes similar-shaped fish.
Keep one per tank unless you obtain a bonded pair, as two unpaired individuals may fight.

It is bold and outgoing once settled, often hovering in the open and interacting with its keeper.
Reef-safe with corals and invertebrates, it integrates smoothly into peaceful community systems.

A good fit for

Beginners wanting a hardy, active fish
Reef community tanks needing midwater interest
Keepers wanting an outgoing, visible fish
Peaceful reefs with corals and inverts

Common mistakes to avoid

Two unpaired blennies will fight
Needs a secure rock retreat to settle
Can jump; a tight-fitting lid helps
Aggressive tankmates may bully it

Is your enclosure big enough?

Minimum volume110 litres (29 US gallons)

CompanyMust be housed alone. One per tank unless a bonded pair

Check your own enclosure against this

Is this urgent?

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.

Work out the cost of a midas blenny

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