Blueline demoiselle
Chrysiptera caeruleolineata
The Blueline demoiselle exhibits striking blue stripes along its body, contrasting with a vibrant yellow-orange abdomen.
This page includes AI-generated images. Why am I seeing AI images?
About the Blueline demoiselle
A little reef damsel with a bright electric-blue line riding over a yellow body, it tends to live deeper on rubble slopes and hugs the bottom in small groups. In aquariums it prefers dimmer light, plenty of rock cover, and frequent small feedings of planktony foods; males guard eggs stuck to the substrate.
Also known as
Quick Facts
Size
6 cm
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
30 gallons
Lifespan
5-10 years
Origin
Indo-West Pacific
Diet
Planktivore-omnivore - small meaty foods (mysis, enriched brine), copepod-rich frozen foods, quality marine flakes/pellets
Water Parameters
23-28°C
8-8.5
Need a heater for this species?
This species needs 23-28°C in a 30 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- A single Blueline demoiselle does fine in 30 gallons; stack plenty of rock to make caves and shaded nooks, and leave some open bottom or rubble to patrol.
- They come from deeper rubble slopes, so keep light on the dim side or provide shaded zones instead of blasting the tank.
- Hold temperature at 23-28 C and pH between 8.0-8.5; they tolerate that range but react badly to sudden swings.
- Feed small, frequent portions of planktony foods: mysis, enriched brine, copepod-rich frozen mixes, plus quality marine flakes or pellets.
- Semi-aggressive damsel behavior applies: in a 30-gallon tank keep one; in larger systems with lots of rock and broken sightlines it can coexist with robust fish, but it may pester timid nano species or other damsels.
- Expect it to stay low in the tank, hugging rock and rubble rather than cruising bright open water.
- If they spawn, the male guards the adhesive eggs on the substrate; raising the larvae is specialized and rarely achieved in display tanks.
- With steady care, this small damsel can live 5-10 years.
Compatibility
Good Tankmates
- Robust clownfish like ocellaris/percula (Amphiprion ocellaris/percula) - similar size and confidence; usually coexist in 30+ gal if there is plenty of rock cover and clear territories
- Cave-oriented basslets such as royal gramma or blackcap basslet (Gramma spp.) - use rockwork, can hold their own, and generally ignore a bottom-hugging demoiselle
- Fang blennies (Meiacanthus spp.) - peaceful but not timid; occupy a different niche and their deterrent bite helps prevent bullying
- Watchman or other sturdy shrimp gobies (Amblyeleotris spp.) - workable with multiple separate burrows/caves; avoid very tiny, shy gobies in tight layouts
- Banggai or pajama cardinalfish (Pterapogon kauderni, Sphaeramia nematoptera) - calm midwater hoverers; provide ample cover and frequent small feeds to reduce chasing
- Reef-safe inverts (cleaner shrimp Lysmata spp., snails, hermit crabs) - typically ignored and make a good clean-up crew
Avoid
- Other damsels and chromis (Chrysiptera, Pomacentrus, Chromis) - similar shape/temperament triggers persistent territorial fighting in smaller tanks; avoid keeping multiples
- Very timid or slow fish like firefish/dartfish (Nemateleotris, Ptereleotris) and assessors - prone to harassment and food competition
- Dottybacks (Pseudochromis spp.) and other small cave bullies - overlapping aggression often escalates in 30-40 gal setups
- Mandarins/dragonets (Synchiropus spp.) and other pod-dependent slow feeders - easily stressed by chasing and outcompeted for food
Blueline demoiselle (Chrysiptera caeruleolineata) is a small Indo-West Pacific damsel with a vivid electric-blue line riding over a yellow body. It stays under 6 cm, lives 5-10 years, and behaves like a bottom-hugging bruiser for its size. In aquariums it appreciates dimmer areas, lots of rock cover, and frequent small feedings. Minimum tank size for a single fish is 30 US gallons. Care level: intermediate.
Origin and natural habitat
Indo-West Pacific. In the wild this species is found deeper than many reef fish, on rubble slopes where it keeps close to the bottom. You will see them in small groups near cover, ducking into gaps between rocks and rubble rather than cruising high in the water column.
Aquarium setup and water conditions
Plan around its bottom-oriented, cover-loving habits. Build rockwork with caves, overhangs, and shaded pockets, and leave some open patches of coarse substrate or rubble along the base. Bright reef lights are fine if you provide darker retreats; these fish are more comfortable and bolder when they have dim areas to retreat to.
- Minimum tank: 30 US gallons for a single fish
- Temperature: 23-28 C
- pH: 8.0-8.5
- Marine system with stable, reef-range salinity and good biological filtration
Create a low-light corridor under ledges or arching rock. This mirrors their rubble-slope habitat and reduces skittish behavior under strong lights.
Diet and feeding
A planktivore-omnivore that does best with small, meaty foods offered in multiple small portions across the day. Aim to keep food suspended so the fish can pick items from the flow and near the bottom.
- Mysis shrimp and enriched brine shrimp
- Copepod-rich frozen blends
- Quality marine flakes and small pellets
Frequent, small feedings curb aggression and keep body condition up, matching the constant picking this fish does in nature.
Behavior and tankmates
Semi-aggressive and territorial, especially around its chosen patch of rock or rubble. It hugs the lower third of the tank and will chase off similar-looking fish that wander too close. In smaller systems it is usually best kept singly. Groups are possible only in larger, rock-heavy tanks with multiple distinct hideouts.
- Choose tankmates that are robust and not easily intimidated.
- Avoid very timid, tiny species that occupy the same lower zones.
- Provide multiple shelters and broken sight lines to diffuse territorial pressure.
Mixing multiple damselfish or closely related Chrysiptera can trigger persistent fighting in confined spaces. If attempted, space and cover must be generous.
Common problems and how to avoid them
- Excess aggression: Use ample rock cover and add this fish after very shy species have settled.
- Light shock/shyness under intense lighting: Provide shaded retreats; do not place its territory directly under the brightest spots.
- Underfeeding: Offer small, planktonic foods several times daily rather than a single large meal.
Similar Species
Other marine semi-aggressive species you might be interested in.
Blackspotted snake eel
Quassiremus ascensionis
A tropical marine snake eel that buries in soft substrates (sand/mud/gravel) with only the head exposed to ambush prey. Recorded to 71 cm TL and occurs mainly in the western Atlantic (also Brazil) and at Ascension Island; typically found in shallow inshore habitats to ~12 m, including sand and seagrass (turtle grass) areas.
Blue blanquillo
Malacanthus latovittatus
A long, slim tilefish with a bold black side stripe and a blue head that fades down the body. It hovers high above the reef and darts back to a sand-rubble burrow, often living as a monogamous pair; in tanks it is fast, jump-prone, and will eat small crustaceans and tiny fish.
Blue Green Chromis (Green Chromis)
Chromis viridis
Blue Green Chromis are those shimmery little green-blue darts you'll see zipping around the top of a reef tank, always looking like they're catching the light just right. They're super fun in a group because they hover and cruise together, but they've got a bit of a "pecking order" thing going on if the tank's tight or the group's too small.
Bluespotted angelfish
Chaetodontoplus caeruleopunctatus
A medium Pomacanthid from the Philippines, it has a dusky body dusted with tiny electric-blue spots and a yellow tail. In the wild it browses sponges and tunicates on deeper reefs, so it thrives only in mature tanks with lots of live rock and frequent feedings.
Broadbarred firefish
Pterois antennata
This is the lionfish with the long "antennae" (those banded tentacles above the eyes) and the ragged, spotty fins that make it look extra dramatic under reef lighting. It'll spend the day tucked under ledges and then cruise out at dusk to ambush shrimp, crabs, and any small fish it can fit in its mouth-also worth remembering it's venomous, so you treat it with respect when you're in the tank.
Comet
Calloplesiops altivelis
This is the famous "Marine Betta" look-alike: jet-dark with those starry spots, and that wild fake eye near the back that makes predators bite the wrong end. It's a super shy cave-dweller by day and then turns into a sneaky night hunter, cruising out for crustaceans and small fish.
More to Explore
Discover more marine species.
Banggai Cardinalfish
Pterapogon kauderni
Banggai cardinals just sort of hover like little underwater satellites, and the bold black bars with those long, polka-dotted fins look unreal under reef lighting. They're super chill most of the time, but once a pair forms you'll see real "fish drama," and the male will even mouthbrood the babies like a champ.
Bicolored foxface
Siganus uspi
A Fiji native with a sharp two-tone look, the bicolored foxface is half deep brown and half yellow with a crisp line between. It spends the day grazing algae and can snap into a mottled camouflage when spooked; those tall dorsal spines are venomous, so other fish usually keep their distance.
Blackfin slatey
Diagramma melanacrum
A large sweetlips from Southeast Asian reefs with a pale silvery-yellow body sprinkled in dark spots and distinct black pelvic and anal fins. Juveniles linger in silty shallows, while adults rest in small groups on deeper reef walls by day and roam at night to pick off crabs, shrimp, and other invertebrates.
Blackspot razorfish
Iniistius dea
This is one of the coolest "knife-bodied" wrasses - it hangs over open sand and, when it gets spooked or wants to sleep, it literally torpedoes straight into the sand. Give it a deep, fine sand bed and it will act totally different (and way more natural) than a typical rock-hugging reef wrasse. Adults are usually shy and cruisy with tankmates, but they are not forgiving about rough handling or sketchy setups.
Blueband goby
Valenciennea strigata
This is that classic gold/yellow-headed sand-sifting goby with the little blue cheek stripe-always busy, always rearranging your sandbed. In a reef tank it'll spend the day taking mouthfuls of sand, filtering out tiny critters/foods, then "snowing" clean sand back out, and it'll usually claim a burrow area (often as a pair in the wild). It's super cool behavior-wise, but you really do need a mature tank with a proper sandbed and a lid because they can jump.
Bluespotted dottyback
Pseudochromis persicus
A striking dark-bodied dottyback covered in tiny blue spots from the Persian Gulf and nearby western Indian Ocean reefs. It grows larger than most dottybacks and throws a lot of attitude for its size, staking out caves and defending them hard. Best for roomy marine setups with robust tankmates and plenty of rockwork to break lines of sight.
Looking for other species?