Saltwater Fish
Mandarin Dragonet
Synchiropus splendidus
Strikingly coloured fish needing a copepod-rich tankAdvanced
- Lifespan
- 5-10 years
- Size
- 2.5-3 in6-8 cm
- Social needs
- One male per tank; a female may be added
- Time
- High
- Cost
- High
- Diet
- Carnivore, live copepods primarily
Overview
What is this animal?
- The Mandarin Dragonet is a strikingly coloured fish, swirled in green, orange, and blue.
- Despite its calm, slow-moving charm, it is an advanced fish because of its specialised diet of small live invertebrates, mainly copepods.
- Most mandarins die slowly of starvation in tanks that cannot sustain a copepod population.
- Success needs a large, mature reef, ideally with a refugium, and patience to establish a thriving food supply.
Temperament
- Peaceful, slow, and shy, it spends the day methodically hopping across rock and sand hunting pods.
- It is reef-safe and harmless to corals and invertebrates, making a calm community fish.
Show 2 more
- Males are territorial toward other males, so keep only one male per tank; a male and female can coexist in a large system.
- Avoid fast, greedy tankmates that outcompete it for food.
A good fit for
- Experienced keepers with mature reefs
- Tanks with a refugium and pod culture
- Aquarists who choose captive-bred, feeding stock
- Patient hobbyists with peaceful communities
Common mistakes to avoid
- Starves without an established copepod supply
- Sold for immature tanks that cannot feed it
- Watch for a pinched, hollow belly
- Greedy tankmates outcompete this slow feeder
Enclosure
Minimum 100 gallons379 litres
Fine alone or with company. One male per tank; a female may be added
- Provide a well-established reef of at least 100 gallons379 L with abundant live rock and a sandbed that hosts copepods: a mature live-rock tank of about that size supports one mandarin, provided nothing else competes for the pods.
- A refugium or pod-culturing system on top of that is strongly recommended to replenish the food supply, and a pair, or a tank with other pod-eaters, needs more.
- A 53 gallon200 L tank is a minimum, and below that size the pods have to be cultured outside the tank, possibly for the fish's whole life.
Show 2 more
- Keep temperature 75-81°F24-27°C, salinity 1.024-1.026, pH 8.1-8.4, and ammonia and nitrite at zero.
- The tank must be biologically mature, never new, before a mandarin is introduced.
Supplies
Setup
- Tank, stand and sump
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
Show 2 more
- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Live copepod bottles for regular top-ups
- Refugium or pod-culture setup
- Refugium macroalgae or pod hotel media
- Frozen cyclops and baby brine shrimp (for trained individuals)
- Small marine pellets (for trained individuals)
Show 2 more
- Turkey baster for target-feeding near the rockwork
- Small thawing cup
Safe substrate: Aragonite sand · Dry or cured live rock
Care routine
Daily
- Check salinity, temperature and flow
- Head-count and look everyone over
- Target-feed a trained fish; otherwise check the pods
- Top up evaporation with fresh water
Every few days
- Service the skimmer and filter socksevery 3 days
Show 9 more
Weekly
- Check the copepod population
- Clean the glass
- Test the water
- Water change
Monthly
- Calibrate the refractometer
- Check salt, RO/DI and reagents
- Harvest and refresh the refugium
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Health review: Monthly pod and belly-profile check, every month
Tools
Care in depth
Diet
Carnivore, live copepods primarily
- A specialised carnivore that grazes copepods and amphipods picked from rock and sand throughout the day.
- A single fish can quickly exhaust a tank's pod population, so a refugium and regular pod top-ups are important.
- Many individuals never accept prepared food, though some can be trained onto frozen cyclops, baby brine, or pellets, and captive-bred mandarins take prepared diets more readily.
- Choose feeding specimens whenever possible.
Health
Signs of good health, and the common problems
- When properly fed, mandarins are reasonably hardy and resistant to ich thanks to a thick protective slime coat.
- The main health risk is slow starvation, visible as a pinched belly and hollow stomach over weeks.
- Quarantine and stable water remain important, but the single best safeguard is confirming the fish eats and maintaining a robust food supply.
- A plump, rounded belly indicates a thriving mandarin.
Is this urgent?
6 warning signs and how fast to act, 3 of them right away
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. Ammonia is directly toxic, and at reef pH more of it is in the toxic form, so a marine system has less margin than a freshwater one. Nitrite is far less toxic in seawater, but any reading in a stocked tank means the biological filter is not keeping up.
NowTemperature 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.
NowRapid 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.
NowToday
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.
TodayCorals 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.
TodayA 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.
TodayQuarantine 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.
Bedding and substrate
2 safe, 3 with a caveat, 2 to avoid
In a marine system the rock and the sand are life support, and how you start them decides the first six months.
Safe
Aragonite sandThe standard marine substrate, and it hosts the biology. It does not meaningfully hold pH or alkalinity at normal reef pH, so test and dose for those regardless.
safeDry or cured live rockDry rock avoids importing pests but takes longer to mature. Cured rock is faster and riskier.
safeWith a caveat
Deep sand bedsPowerful nutrient processing when they work and a sulphide release when they are disturbed. Choose shallow or deep deliberately, not by accident. A sand-sifting or burrowing goby needs a fine bed about 2 to 3 in5 to 8 cm deep that it turns over itself. That is a different thing from a denitrifying deep sand bed (4 in10 cm or more, left undisturbed), and the two do not mix: a sifting goby disturbs the layers a deep sand bed depends on and eats the life in it.
with a caveatUncured live rockIt will cycle the tank for you, and it will also bring in whatever was living in it.
with a caveatBare bottomWorkable in high-flow systems for fish that neither sift nor burrow, but it removes a large part of the biological buffer. Wrong for watchman gobies and other gobies that burrow or sift, which need a fine sand bed at least 2 in5 cm deep to dig and feed in, and for mandarins and other copepod-eaters, which need sand as well as mature rock for their food to breed in.
with a caveatNever
Silica play sandNot the marine standard, and commonly blamed for feeding diatom blooms in a new tank.
neverAny rock or decor of unknown originMetals and phosphate leach for months and are almost impossible to trace once the tank is running.
neverThis is our general list for saltwater fish. We have not built one specific to Dragonets yet.
Top resources for more info
Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-10-22.
YouTubers
HumbleFish & ReefSaltwater fish disease, quarantine and treatment (Humble.Fish forum)BRStvReef tank setup, fish health and quarantine series (run by a retailer)FishOfHex AquaticsBeginner saltwater guides, avoiding common mistakes and tank disasters
Sites
Keep going
Other Saltwater Fish worth knowing
Same axes, same care guides: the honest way to compare them.
