Saltwater Fish · Gobies
Yellow Watchman Goby
Cryptocentrus cinctus
Bright-yellow sentry that shares a pistol-shrimp burrowBeginner
- Lifespan
- 4-6 years
- Size
- 3-4 in8-10 cm
- Social needs
- Singly or pair; pairs with a pistol shrimp
- Time
- Daily feeding; weekly testing/changes
- Cost
- High
- Diet
- Carnivore (mysis, brine, marine pellets)
Overview
What is this animal?
- The Yellow Watchman Goby is a stocky, bright-yellow (sometimes grey) goby known for its symbiotic partnership with pistol shrimp.
- The near-blind shrimp digs and maintains a burrow while the sharp-eyed goby stands guard, retreating into the shared den at any danger.
- It is hardy, peaceful, and reef-safe.
Show 2 more
- Even without a shrimp it makes a charming bottom-dweller, perched on the sand watching the tank with its large eyes.
- With its shrimp partner it shifts sand around the burrow, but it is a light sifter, not a sand-bed cleaner like the Diamond Watchman.
Temperament
- Peaceful and reef-safe, the Yellow Watchman spends its time guarding its burrow and watching the tank.
- It is harmless to corals and most tankmates but may squabble with another bottom-dwelling goby over territory.
Show 2 more
- Keep one per tank unless adding a bonded pair, and avoid housing it with larger predators or very aggressive fish.
- With its pistol-shrimp partner it shows interesting cooperative behaviour that makes it a standout reef resident.
A good fit for
- Beginners wanting interesting behaviour
- Sand-bedded reef tanks
- Keepers wanting the pistol-shrimp pairing
- Peaceful community stocking
Common mistakes to avoid
- No lid - they jump from the tank
- Shallow sand prevents natural burrowing
- Rock stacked on sand can collapse on burrows
- Aggressive tankmates outcompete it for food
Enclosure
Minimum 79 gallons300 litres
Fine alone or with company. Singly or pair; pairs with a pistol shrimp
- Provide a cycled tank of at least 80 gal300 L with a deeper sand bed (2 in+5 cm+) for burrowing and live rock placed on the glass so digging cannot collapse it.
- Keep salinity 1.024-1.026, temperature 74-80°F23-27°C, pH 8.1-8.4, and nitrate low.
- A secure lid is important because, like other gobies, they jump.
Show 2 more
- Pair it with a single Tiger or Randall's pistol shrimp for the classic partnership.
- Stable water and a soft sand bed it can excavate keep this goby content and natural in behaviour.
Supplies
Setup
- Tank, stand and sump, about 80-90 US gallons300-340 litres
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
Show 2 more
- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Frozen mysis shrimp
- Frozen enriched brine shrimp
- Frozen cyclops
- Micro marine pellets
- Copepod bottle or refugium culture
Show 2 more
- Turkey baster or pipette for target-feeding
- Small thawing cup and fine strainer
Safe substrate: Aragonite sand · Dry or cured live rock
Care routine
Daily
- Check salinity, temperature and flow
- Check the lid and every gap
- Feed
- Head-count and look everyone over
- Top up evaporation with fresh water
Every few days
- Service the skimmer and filter socksevery 3 days
Show 8 more
Weekly
- Clean the glass
- Test the water
- Water change
Monthly
- Calibrate the refractometer
- Check salt, RO/DI and reagents
- Top up sand-bed life
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Health review: Quarterly review with a lid check, every 3 months
Tools
Care in depth
Diet
Carnivore (mysis, brine, marine pellets)
- The Yellow Watchman is a carnivore.
- Offer frozen mysis and brine shrimp, finely chopped seafood, and sinking marine pellets, fed once or twice daily.
- It will also sift the sand for tiny morsels and microfauna.
- Most individuals feed readily once settled, though shy ones eat more confidently with their pistol-shrimp partner present.
- Ensure food reaches the bottom, as this goby rarely chases food high in the water column and can be outcompeted by faster fish.
Health
Signs of good health, and the common problems
- Watchman gobies are hardy and disease-resistant in stable water.
- The main risks are jumping from an open tank and stress from aggressive tankmates or unstable parameters, which can lead to ich or bacterial infection.
- Quarantine new fish, keep nitrate low, and provide secure burrows.
- Watch that it is getting enough food, since a thin, hollow-bellied goby signals it is being outcompeted.
- A calm, sand-bedded tank keeps it healthy for years.
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 Gobies 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
Gobies, side by side
Same axes, same care guides: the honest way to choose between types.
