Care guide · Marine fish

Royal gramma

Gramma loreto

Photo: Brian Gratwicke · Source · CC BY 2.0Resized and compressed; no cropping or colour changes.

The royal gramma combines a purple front half with a yellow rear half and makes a sheltered rock crevice its home. Gramma loreto is a Caribbean reef fish that is often calmer than its vivid colours suggest. Nevertheless, it defends its cave, particularly against its own species and similarly shaped intruders. It can suit a beginner with a mature marine aquarium, provided the layout offers overhangs and separate refuges. It does not need to swim constantly in the centre of a bare tank. Hanging beside a vertical surface or beneath an overhang can be normal behaviour. Judge its welfare by feeding, breathing and changes from its usual routine. A single specimen is the cautious choice for an ordinary community aquarium; keeping a group requires a different scale and preparation, not simply a few extra litres on paper.

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At a glance

Adult size: Approximately 8 cm
Aquarium length: At least 80 cm
Minimum aquarium volume: At least 120 L
Temperature: 24–26 °C
Specific gravity (SG at 25 °C): 1.024–1.026 SG
Salinity: 32–35 ppt
pH: 8.1–8.3
Difficulty: Easy
Temperament: Territorial
Diet: Carnivore
Swimming zone: Middle
Reef safety: Generally reef safe
Suitable for beginners: Conditional
Social needs: Solitary
Keeping conspecifics: Prefer one individual

Cautious husbandry guidance for adults, not a complete stocking calculation. Assess tank length, layout and the entire community together.

About this species

Plan for an adult length of about 8 cm. The transition between purple and yellow, together with the dark markings near the eye and on the dorsal fin, helps identify the species. The similar Pictichromis paccagnellae belongs to another family and may behave differently; a sales description saying only “purple and yellow” is inadequate. Ask specifically for Gramma loreto. Colour intensity and individual size do not reliably identify sex or establish that two fish form a compatible pair.

Natural habitat

Royal grammas inhabit rocky reef structures in the western Atlantic and Caribbean. Overhangs, caves and vertical walls provide a base from which to catch small food particles. A fish may orient itself to the surface rather than the horizon. Reproduce this with shaded cavities and open water nearby. A brightly lit reef aquarium can work if the fish can choose shade. It should not be forced to occupy the exposed front of the tank merely to make it easier to see.

Aquarium and layout

Use approximately 120 L and 80 cm of tank length as a cautious lower planning limit for one adult, not as a calculated stocking capacity. Build stable rockwork with several entrances and small cavities so that one dominant animal cannot guard every refuge. Leave space between its home and a clownfish or dwarf angelfish territory. Moderate flow should carry food past the cave without dislodging the fish. Cover openings and ensure digging tankmates cannot undermine newly placed rocks.

Water conditions

Stable seawater within the central profile supports acclimatisation. Measure salinity with an instrument whose scale and calibration you understand: specific gravity and ppt are not the same number. Replace evaporation with suitable fresh water. Check nitrogen compounds during maturation and after stocking changes, and follow nitrate as a maintenance indicator. Match maintenance to actual feeding and stocking. A low reading on one day does not prove biological stability. Do not change pH or salinity abruptly to imitate a different source’s recommendation.

Behaviour and group size

Defence is usually concentrated around the cave. A brief open-mouth threat can occur during territorial encounters, whereas prolonged pursuit and damaged fins indicate a problem. Arrange alternative routes for other fish. A gramma that remains permanently hidden may be intimidated rather than ill. Also check whether food is offered close enough to its home for it to eat. Watching food disappear elsewhere in the aquarium does not establish that this fish has received its share.

Social behaviour and conspecifics

One specimen is the clearest choice for an ordinary home aquarium. Social groups can be kept in large, carefully arranged systems, but adding an arbitrary second fish to an established territory is risky. More caves do not replace suitable selection and introduction. The planner therefore does not interpret several individuals as an accepted pair or suitable group. If a pair is offered for sale, ask how sustained mutual acceptance was established and keep a practical way of separating them available.

Feeding

Royal grammas mainly take animal food. Offer suitably small marine food that the fish demonstrably accepts, supplemented with appropriate mysis, enriched brine shrimp or other fine animal foods. Food must reach the cave entrance or adjacent water column. A fast-swimming neighbour can intercept most of it. Distribute small portions across more than one location and watch until each fish eats. Products are linked only after their formulation, application and feeding form have been checked; an empty product list does not make feeding optional.

Reef safety

The royal gramma is generally regarded as reef safe and is not a usual coral feeder. This agrees with its diet of small animal food particles. Nevertheless, avoid absolute promises covering every coral or invertebrate species. Its cave may sit directly beneath a coral, so maintenance or new neighbours there can provoke territorial defence. Separate risk categories distinguish direct evidence from limited information. A host anemone is not required.

Keeping with other fish

Calm cardinalfish and a suitably kept ocellaris can be neighbours if their permanent refuges are separated. A shy firefish needs its own escape hole. A dominant six-line wrasse or dwarf angelfish may restrict feeding and visibility even when water requirements overlap. Large predators do not belong in a small gramma aquarium. Consider adult size, territories and swimming routes together. Introduce shy residents before a dominant cave-dweller claims the entire layout whenever practical.

Keeping with invertebrates

Adult cleaner shrimp and larger common reef snails present a different situation from tiny ornamental shrimp. As a carnivore, the gramma may take very small moving prey; do not expect shrimp offspring to grow up safely beside it. Invertebrates need accessible cover outside the defended cave. A general guarantee for starfish, sea urchins or particular worm groups is not justified by the available species-specific information. Gaps remain explicitly marked instead of being replaced by the general reef-safe label.

Breeding

Captive breeding is established. Spawning takes place at a sheltered nest site, after which eggs and small larvae require different care. Selecting a compatible pair and raising larvae demands experience and appropriate fine live food. This care guide is not a complete breeding protocol. Do not combine unknown adults merely to provoke spawning. An established combination observed at a breeder or retailer provides more useful information than guesses about sex based only on colour.

Possible problems

A gramma occasionally hanging upside down along a cave wall need not be ill. Sudden loss of balance, heavy breathing, wasting, injury or refusal of familiar food are warning signs. Check competition and water quality before drawing conclusions. Repeatedly rebuilding the rockwork to see the fish removes its secure home. Persistent problems need targeted advice. Do not medicate a mixed reef without assessing the treatment’s effects on corals and all the other invertebrates present.