One per tank (groups only in large systems added together); fights its own kind and lookalikes
Diet
Carnivore (mysis, brine, marine pellets)
Time
Daily feeding; weekly testing/changes
Cost
Medium-high
Overview
The Blackcap Basslet is the Royal Gramma's deep-water Caribbean cousin, dressed in a single sheet of rich magenta with a jet-black cap that runs from the snout, over the crown, and back along the entire dorsal fin.
It grows slightly larger than its famous relative, reaching about 10 cm (4 in), and carries itself with noticeably more confidence.
In the wild it lives on steep reef walls at roughly 15-60 m (50-200 ft), far deeper than the Royal Gramma, orienting its belly to the nearest surface so it appears to hover upside-down beneath ledges before vanishing into crevices.
That deep-water origin makes wild specimens pricier and makes choosing a healthy, properly decompressed individual the most important decision you will make.
Once settled, it is hardy, long-lived, and fully reef-safe.
Housing
Give it a cycled aquarium of at least 110 L (30 gallons) with generous live rock stacked into caves, tunnels, and overhangs it can hang beneath.
Coming from dim, deep walls, it prefers shaded zones under ledges to a bright, open aquascape, and in a tank without cover it will simply stay hidden.
Keep salinity at 1.024-1.026, temperature 23-26°C (74-79°F), pH 8.1-8.4, and nitrate under 20 ppm (lower still in a coral-heavy reef).
A tight-fitting lid is non-negotiable, because like all grammas it is a proven jumper.
Arrange the rock to break lines of sight so it can hold a home cave without confronting every passing tankmate.
Diet
In the wild the Blackcap Basslet picks zooplankton and small crustaceans from the water column beside its wall.
In the aquarium feed frozen mysis, enriched brine shrimp, finely chopped seafood, and a quality sinking marine pellet, offered once or twice daily.
Freshly imported fish can be hesitant feeders, so drift frozen food near its cave until it eats confidently in the open.
A varied meaty diet keeps the magenta deep and the black cap crisp.
Feed small portions and check that faster tankmates are not intercepting every meal.
Health
Once established this is a hardy, disease-resistant fish that commonly lives 5-10 years.
The routine risks are marine ich and bacterial infection following stress, so quarantine new arrivals and keep parameters steady.
The species-specific risk sits at the point of purchase: wild fish are collected deep, and poorly decompressed specimens carry swim-bladder damage that shows as tilted swimming, floating, or listless sulking.
Only buy a fish that swims level and eats in front of you, and choose captive-bred stock (now produced by several breeders) whenever you can find it.
Persistent hiding and refused food are the early warning signs to act on quickly.
Temperament
The Blackcap Basslet is peaceful toward unrelated species but runs a notch feistier than the Royal Gramma, chasing intruders from its cave with real intent rather than pure bluff.
It is reef-safe and ignores corals and all but the tiniest ornamental shrimp.
In tanks of the size it is usually kept, house just one; conspecifics only coexist in a much larger system when introduced together.
Never pair it with a Royal Gramma or with dottybacks, because the similar shape and colours trigger persistent fighting in ordinary-sized systems.
With dissimilar, peaceful tankmates and plenty of rockwork it becomes a confident fixture, patrolling openly and hovering at odd angles beneath its favourite ledge.
A good fit for
Reef tanks with shaded, cave-rich rockwork
Keepers who loved the Royal Gramma and want a step up
Smaller marine systems from 30 gallons
Fans of upside-down ledge-hovering behaviour
Common mistakes to avoid
Deep-collected fish with swim-bladder damage — buy level swimmers that eat
Mixing with Royal Grammas or dottybacks (fighting)
Bright, bare aquascapes keep it hidden and stressed
Open-top tank leads to jumping
Costs noticeably more than a Royal Gramma
Is your enclosure big enough?
Minimum volume110 litres (29 US gallons)
CompanyMust be housed alone. One per tank (groups only in large systems added together); fights its own kind and lookalikes
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
Beginner
Intermediate
Intermediate
Intermediate
Intermediate