A Blackcap Basslet (Gramma melacara) brings a bold splash of deep purple and a distinct, slanted black cap to your reef. Expect a fish that hugs the rockwork, watches from the shadows, and forms a strong attachment to its favorite hiding spot. It may arrive shy, then become more assertive as it settles.
I recommend a 20 US gallon minimum for a single Blackcap, with a usable shaded retreat, suitable tankmates, and a setup where you can make sure it gets food. That advice draws on my experience keeping Royal Grammas and similar species. Your aquascape and adult fish community matter just as much as the water volume.
Species Snapshot
| Topic | Blackcap Basslet at a glance |
|---|---|
| Scientific name | Gramma melacara, family Grammatidae |
| Appearance | Purple to blue-purple body with a slanted black cap over the head and nape |
| Adult size | Around 4 inches |
| Minimum recommendation | 20 US gallons (about 76 L) for one fish, with suitable shelter and stocking |
| Temperament | Often shy at first; can defend its chosen cave |
| Diet | Carnivore; small meaty marine foods |
| Reef compatibility | Generally coral-safe; tiny ornamental shrimp may be at risk |
| Temperature | Approximately 76–78°F (24–26°C), kept stable |
| Social recommendation | One Blackcap for a typical community aquarium |
Blackcap Basslet vs. Royal Gramma
The easiest way to tell them apart is the color pattern. A Blackcap has a purple body with its signature black cap sloping across the upper head and onto the front of the back. A Royal Gramma (Gramma loreto) has a purple front, yellow rear, and a dark spot near the front of its dorsal fin. They are different species, not color morphs.
Look for the Blackcap’s large eye, short snout, slender compressed body, and concave tail. Its apparent shade of purple changes with the lighting. These features help identify the fish without relying on one exact color in a seller’s photograph.
Blackcaps, also sold as Blackcap Grammas, come from western Atlantic and Caribbean reefs, where they use steep reef faces, ledges, and recesses. They generally occur deeper than Royal Grammas. Similar looks don’t guarantee identical behavior, so assess cave competition in your own aquarium before choosing either species.
Plan around an adult Blackcap of roughly 4 inches. Published maximum lengths are 10 cm total length and 11 cm without a stated measurement convention, so treat that size as a guide. For the other side of the comparison, see the Royal Gramma care guide.
Tank Size, Shelter, and Water Conditions
My 20-gallon recommendation is for one Blackcap. Some suppliers, including LiveAquaria and Biota, suggest 30 gallons or more. The extra space gives you more room to arrange rockwork and separate territories.
Before adding one, check four things:
- A usable retreat. Provide a shaded cave the fish can enter and shelter inside. An exposed decorative arch may offer little protection.
- Broken sight lines. Arrange the rockwork so another fish isn’t constantly watching the Blackcap’s front door.
- A suitable adult community. Look at who already claims the rockwork and how your other fish will grow. A persistent cave competitor can make even a larger tank unsuitable.
- Observable food access. Food must reach the Blackcap near its shelter, and you need to be able to see it eat.
If another fish already controls the intended retreat, change the layout or stocking plan first. Use a fitted cover, too: Blackcaps can jump from an uncovered aquarium.
Water Parameters and Lighting
Approximately 76–78°F (24–26°C) is a practical temperature recommendation for this guide. Keep conditions steady. In a reef system, specific gravity around 1.024–1.025 and pH 8.1–8.4 are useful targets within the supplier guidance reviewed here; account for the needs of your other inhabitants and measure consistently.
Provide localized shade with rockwork while lighting the rest of the aquarium for your corals. A deeper-water origin doesn’t mean the whole tank must be dark or that you automatically need a chiller. The useful goal is an accessible, shaded refuge.
Temperament and Compatibility
Blackcaps are generally coral-safe, but that doesn’t guarantee the safety of tiny ornamental shrimp or other small crustaceans. Keep coral compatibility and prey risk as separate questions when choosing your fish.
A shy fish can still defend its favorite cave. For a typical community aquarium, I recommend one Blackcap. Pay particular attention to other basslets and cave competitors that might block its retreat or steal its meals. Predator-sized tankmates and persistent bullies are poor choices.
Watch what happens around the cave and at feeding time. Each fish should be able to use shelter and eat without persistent interference. Have a separation plan if harassment prevents feeding. If tiny ornamental shrimp are a priority, weigh that risk before adding a Blackcap.
Feeding: Watch Them Eat
Blackcaps are carnivores. Offer varied, appropriately sized meaty marine foods, such as small mysis shrimp. Small meals two or three times daily are a useful starting routine; adjust portions to what the fish eats and remove uneaten food. Captive-bred juveniles may already be accustomed to tiny pellets, but ask what your particular fish takes.
The key is observation. Find the spot where the Blackcap waits near its cave, present food where it can intercept it, and watch it capture and swallow the food. Feeding the water column doesn’t tell you whether the hidden fish got a meal.
If another fish keeps your Blackcap pinned inside the rocks, rethink the food presentation, shelter arrangement, or stocking list. Repeatedly adding more food can increase waste without solving the problem. Persistent refusal to eat deserves closer attention.
Buying and Settling a Blackcap
Successful captive breeding has brought captive-bred Blackcaps into the hobby, although availability varies. Check the origin and feeding history of the individual you’re buying.
Ask the seller:
- Is it captive-bred or wild-caught? Find out what is known about its source.
- What is it eating? Ask to see it feed when buying in person, or request a specific feeding history.
- Is it swimming with control and using shelter normally? Assess the actual fish, not just its photograph.
- What transfer instructions apply? Follow the supplier’s advice for that shipment and packing method.
Have the retreat and feeding plan ready before it arrives. Captive-bred status doesn’t guarantee freedom from disease, and a deep-water origin alone doesn’t diagnose a capture-related injury. If the fish persistently loses swimming control, assess the actual problem rather than assuming an acclimation or decompression treatment from its species name.
When comparing prices, check size, origin, shipping charges, and feeding history. Don’t assume a fixed Blackcap price premium over a Royal Gramma.
Common Blackcap Behavior Questions
Why Is My Blackcap Hiding?
Shelter use is normal, especially in a new aquarium. Make sure another fish isn’t trapping it in the cave and that it emerges far enough to get food. A Blackcap may spend substantial time out of view, so choose one because you enjoy that relationship with the rockwork.
Is Swimming Upside Down Normal?
Yes. A controlled, inverted posture close to the underside of a rocky ledge can be normal. Floating, losing swimming control, or struggling to breathe needs a different assessment; the normal shelter behavior doesn’t explain every unusual posture.
Can I Keep Two Blackcaps or Add a Royal Gramma?
For a 20-gallon aquarium, I recommend one Blackcap and no other grammas. Pairs and groups have been maintained successfully, but pairing can be difficult and their needs go beyond this single-fish recommendation. More space, introduction history, territory, and feeding access all matter; have a way to separate fish if the combination fails.
If you’re interested in a breeding pair, don’t try to identify a mate from cap size or purple coloration. Those features don’t provide a reliable external sexing rule.
Is a Blackcap Right for My Aquarium?
A single Blackcap can be a good choice if you have at least the recommended 20 US gallons, an available shaded retreat, suitable neighbors, and a feeding routine that gives it a fair share. Expect a fish with a strong attachment to its cave that can become more assertive as it settles.
Reconsider if another fish controls the shelter, tiny ornamental shrimp are a priority, or you want a fish that stays continually visible in open water. For other options, explore the 20-gallon saltwater fish guide.
Illustrations generated with AI using species references.