Blueline demoiselle
Chrysiptera caeruleolineata
The Blueline demoiselle exhibits striking blue stripes along its body, contrasting with a vibrant yellow-orange abdomen.
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About the Blueline demoiselle
This is one of those damsels that looks like it should be a little terror, but its vibe is way more chill than the classic blue devils. You get that bright blue body with a clean line detail, and it spends a lot of time zipping low around the rockwork like it owns a tiny little neighborhood.
Also known as
Quick Facts
Size
6 cm
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
20 gallons
Lifespan
5-8 years
Origin
Indo-West Pacific
Diet
Omnivore - quality marine pellets/flakes plus frozen foods; will also pick at algae/film
Water Parameters
24-28°C
8.1-8.4
8-12 dGH
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Calculate heater sizeCare Notes
- Give them rockwork with lots of little holes and ledges - they claim a nook and will chase anything that drifts too close.
- They do great in normal reef numbers: ~1.020-1.025 specific gravity, 75-79°F (24-26°C), pH 8.1-8.4, and keep ammonia/nitrite at zero.
- A single fish can work in a 20-30g, but if you want a pair or more, go bigger and break up sight lines with rock so one bully cannot patrol the whole tank.
- Feed small meaty stuff once or twice a day: pellets, mysis, brine with enrichment, chopped seafood - they are not picky, just do not let them get chunky.
- Tankmates: they're usually fine with clowns, gobies, blennies, wrasses, and most peaceful reef fish, but skip other damsels or similar-shaped fish in small tanks unless you like drama.
- Add them late if you are building a community tank; if they go in first, they act like they own the place and can make new additions miserable.
- If they start picking on a shy fish, rearrange a bit of rockwork or add another hide; sometimes moving their territory around breaks the pattern.
Compatibility
Good Tankmates
- Other chill reef community fish that hold their own, like small wrasses (pink-streaked, possum wrasse) - the blueline will mostly just do its own thing and dart around the rockwork
- Clownfish (ocellaris or percula) - they usually ignore each other, just give both a bit of personal space so the damsel does not claim the whole rock pile
- Small gobies that stick to their lane (watchman goby, clown goby, neon goby) - they are quick and low-drama, and the demoiselle typically does not bother them much if there are plenty of holes to duck into
- Blennies with attitude but not mean, like a tailspot blenny - perching fish that graze and mind their business tend to be fine in a normal reef setup
- Cardinals (banggai or pajama) - calm midwater fish that do not compete for the same hidey-hole, and they are not usually pushovers if the damsel does a little posturing
- Small tangs or rabbitfish in bigger tanks (tomini kole tang, one-spot foxface) - they are way too big to be intimidated and they keep the overall vibe steady, just do not cram them in a nano
Avoid
- Other damsels, especially other Chrysiptera or multiple bluelines in a small tank - this is where the 'peaceful damsel' thing falls apart and you get nonstop chasing and cornering
- Slow, shy fish that do not like being buzzed, like firefish and dartfish - bluelines can decide they own the rockwork and keep these guys pinned in a corner
- Seahorses and pipefish - they are slow feeders and easy to stress, and even a 'mellow' damsel can turn feeding time into a bad day for them
Where they come from
Blueline demoiselles (Chrysiptera caeruleolineata) are little Indo-Pacific reef fish. In the wild they hang around shallow coral and rubble zones, weaving in and out of cracks and branching coral like they own the place.
That wild lifestyle explains most of their aquarium personality: bold, quick to claim a corner, and happiest when they have a bolt-hole they can vanish into.
Setting up their tank
You do not need a huge tank for a single blueline, but you do want enough rockwork that it can pick a home and still leave everyone else some space. Think in terms of structure more than gallons: caves, overhangs, and a few tight crevices.
- Rockwork: build a few distinct "zones" so territories feel separated
- Flow: moderate reef-style flow is fine, they are strong swimmers
- Lighting: whatever your reef has, they do not care as long as there is cover
- Lid: they can jump if spooked, especially new arrivals
If you are adding one to an established tank, rearranging a bit of rock right before introduction can dial down the "this is my turf" attitude from existing fish.
They look small and friendly at the store. In a tiny tank with minimal rock, they can turn into a little blue bouncer that harasses anything that comes near their favorite cave.
What to feed them
Feeding is the easy part. These are classic damsels: they eat fast, they eat often, and they are not picky once settled.
- Staples: quality marine pellets and flakes (small size)
- Frozen: mysis, brine shrimp (better if enriched), chopped krill, reef blends
- Occasional: tiny bits of nori or herbivore foods (they will peck at it)
If you have slower, shy fish, feed in two spots. Damsels will bulldoze the buffet line, and splitting food helps everyone else get their share.
I have the best luck with small meals once or twice a day. They stay chunky without turning your nutrients into a science project.
How they behave and who they get along with
Bluelines are on the feistier end of the Chrysiptera group. Not "terror of the tank" like some damsels, but they are confident and they do not bluff. Once they pick a cave, they will defend it.
- Good tankmates: clownfish, most wrasses, gobies (with enough space/hiding), tangs, foxfaces, reef-safe angels in bigger tanks
- Use caution: very timid fish (firefish, small assessors) in smaller setups
- Usually a bad mix: other damsels in cramped tanks, especially similar-looking blue species
If you want more than one, it usually goes best in a larger tank with lots of rock and adding them at the same time. One established blueline often does not welcome a new blueline roommate.
They are reef safe in the sense that they do not eat corals. The main "reef problem" is social: they can stress out peaceful fish if the layout does not give everyone an exit route.
Breeding tips
They can spawn in home aquariums, and you will sometimes see the classic damsel routine: a male claims a spot (usually a cave or underside of rock), cleans it, and tries to lure a female in. After spawning, the male guards the eggs and fans them.
- Look for: a chosen nest site, extra chasing, and the male spending lots of time in one cave
- Eggs: tiny and stuck to the surface, guarded closely
- Hatch: typically at night, larvae go into the water column
Raising the fry is the hard part. You will need a separate larval setup and live foods (rotifers first, then baby brine). In a normal display tank, the larvae become plankton snacks pretty quickly.
Common problems to watch for
Most issues I have seen with bluelines are not mysterious diseases, they are "fishkeeping physics": stress from bullying, stress from being the bully in a too-small box, and the usual saltwater newbie pitfalls.
- Aggression: torn fins on tankmates, constant chasing, fish pinned to a corner
- Jumping: especially during the first week or after a scare
- Ich/velvet: they are hardy, but they can still carry or catch it like any other fish
- Starving shy fish: damsels eat first and fastest, so watch your quieter fish closely
Do not use a blueline demoiselle as a "starter fish" to cycle a tank. They might survive it, but it sets you up for long-term aggression and health issues in a tank that is still finding its balance.
If one turns into a bully, the fix is usually layout and space: add more rock cover, break up sight lines, and consider moving the damsel (or the victim) if the tank is small. Some individuals mellow out, some never do.
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