Small Chinese silver-biddy
Gerres decacanthus
The Small Chinese silver-biddy has a compressed body, silver coloration, and distinctive five to seven dorsal spines.
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About the Small Chinese silver-biddy
Think of a quick, silvery sand-sifter that cruises shallow bays and estuaries, flashing as it turns. In a tank it uses that stretchy mojarra mouth to puff sand and pick tiny critters, and it really settles in when kept as a small group with open swimming space and a soft sand bed.
Also known as
Quick Facts
Size
15 cm
Temperament
Peaceful
Difficulty
Intermediate
Min Tank Size
55 gallons
Lifespan
4-8 years
Origin
East Asia
Diet
Carnivore - sifts sand for small benthic invertebrates; accepts frozen and sinking prepared foods
Water Parameters
24.7-29.1°C
7.8-8.4
11-22 dGH
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This species needs 24.7-29.1°C in a 55 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give them room - a 75g tank or bigger for a group - with fine sand 1-2 inches deep and lots of open swimming space; sharp gravel tears up their sifting mouths.
- Run brackish water at SG 1.010-1.018 for juveniles and move them up to 1.018-1.022 as they mature; keep 24-28 C, pH 7.6-8.3, hard and alkaline.
- They are messy sand-sifters, so push strong filtration and brisk flow - shoot for 6-10x turnover and plenty of surface agitation.
- Feed sinking meaty foods like mysis, chopped prawn, clam, and quality pellets; 2-3 small meals beat one big dump, and they like to nose through sand while eating.
- Keep them in a group of 4+ or they get skittish and nose-bash the glass; tight lid, because they jump when startled.
- Tankmates: fast, robust brackish fish like scats, monos, and archerfish work; avoid shrimp, tiny fish, and slow long-finned species that get bullied or inhaled.
- Do water changes weekly and keep nitrate under 30 ppm; match salinity and temp on new water and use marine salt mix only.
- Breeding in home tanks is basically nil - they are pelagic spawners that head seaward, so do not plan a project around it.
Compatibility
Good Tankmates
- More of their own kind - keep silver-biddies in a 5+ group so they school and stay chill
- Fast, brackish schoolers like monos and scats of similar size - same salinity and pace, works great in a roomy tank
- Topwater archerfish - they hang up high and ignore the biddies sifting mid-bottom
- Green chromides of similar size - peaceful grazers that handle hard, slightly salty water
- Adult sailfin mollies and other big livebearers in mid to strong brackish - tough enough not to get pushed around
- Medium brackish gobies like knight gobies - bottom dwellers that are quick at feeding time
Avoid
- Nippy puffers like figure 8 or green spotted - they will harass and bite fins
- Tiny or dainty fish like bumblebee gobies, guppies, or glassfish - get outcompeted or end up as snacks
- Big predators such as Columbian shark catfish or brackish morays - sooner or later, someone gets swallowed
- Delicate slow feeders like violet gobies - the biddies fast, constant foraging leaves them hungry and stressed
Where they come from
Small Chinese silver-biddies (Gerres decacanthus) are inshore wanderers from Asia and the Indo-West Pacific. You see them around mangroves, mudflats, and estuaries, cruising over sand and sifting for snacks. Juveniles push up into brackish creeks, then many slide more marine as they grow.
They are classic silver-biddy mojarra types with a mouth that shoots forward like a straw. That lets them vacuum the sand and spit out puffs, which is half the fun of keeping them.
Setting up their tank
They are fast, schooling fish that use the entire tank. A single juvenile can ride in a 40 breeder for a while, but a group needs space. For 4 to 6 fish, think 75 to 120 gallons with strong filtration and lots of open swim room.
- Salinity: 1.005-1.012 for small juveniles, inch upward to 1.015-1.020 as they mature
- Temperature: 75-82 F (24-28 C)
- pH: 7.6-8.2, keep it steady
- Hardness: medium-high; they like mineral-rich water
Use fine sand. They constantly mouth the substrate, and sharp gravel will tear lips. I keep the scape simple: open areas, a few smooth rocks or mangrove-style roots, and nothing fragile because they dig.
Flow and oxygen matter. They are estuary sprinters, so give them brisk circulation and a tight lid. They jump, and they do it well.
Aim for 8-10x tank turnover with a canister or sump plus a powerhead. Surface agitation keeps them happy and reduces sulking.
Salinity swings zap them. Top off with freshwater daily to keep SG stable, then do measured changes with pre-mixed brackish water.
What to feed them
They are sand-sifters that lean carnivorous. Mine switched between hunting and midwater snatching. Small, frequent meals keep them in good shape.
- Frozen mysis and chopped prawn
- Bloodworms and blackworms (rinsed well)
- Quality sinking carnivore pellets and soft wafers
- Brine shrimp is fine as a snack, not a staple
- Occasional crushed clam or mussel for variety
They learn pellets, but start with frozen to wake up their feeding response, then mix in pellets over a week or two.
Target-feed with a turkey baster near the sand. They will sift, spit, and circle back to catch the good bits.
How they behave and who they get along with
Silver-biddies are social and feel bolder in a group. Solo fish pace and spook more. In a small school they settle, form loose ranks, and spend more time sifting than freaking out at shadows.
- Good tankmates: archerfish, monos, scats, larger mollies, orange chromides, larger bumblebee gobies, and Colombian shark catfish if you have a very large system
- Sketchy tankmates: slow, long-finned fish like bannerfish or bettas (they will nip)
- Do not mix with: tiny livebearers or shrimp you care about. They are snacks.
They are not bullies, but they feed fast and can nip during feeding frenzies. Keep groups size-matched to cut down on one big bruiser running the show.
You will see faint bars appear and vanish as they shift mood. Bars up usually means keyed-in and alert, not necessarily stress.
Breeding tips
I have not seen a confirmed home spawning for this species. In the wild they spawn in coastal waters and the eggs drift. Sexing is not obvious, and they likely need seasonal cues, big water volume, and marine salinity to even consider it.
If you are determined, raise a large, stable group, step salinity toward 1.018-1.022 at maturity, and run dawn-dusk lighting with heavy feeding before simulated monsoon water changes. Expect nothing, and you will not be disappointed.
Common problems to watch for
- Jumping: tight lids with blocked gaps are non-negotiable
- Mouth injuries: rough netting or sharp substrate damages their protrusible mouths
- Ich and velvet: show up after stress or salinity dips; brackish slows some pests but does not stop them
- Ammonia spikes: they are messy eaters; overfilter and rinse sponges often
- Refusing dry food: wean with frozen-first, then pellets mixed in
- Bullying by larger, boisterous brackish fish: watch feeding time and add more stations
Do not swing from low brackish to near-marine in one go. Move 0.002-0.003 SG per week, max. Rapid shifts cause osmotic shock and secondary infections.
Quarantine new arrivals. Many come wild-caught from estuaries and bring flukes. A simple observation period and gentle deworming saves headaches.
Use a container to catch them instead of a rough net. Their lips catch on mesh and tear easily.
Similar Species
Other brackish peaceful species you might be interested in.
African moony
Monodactylus sebae
This is that shiny, diamond-shaped "mono" that cruises around in a tight pack and looks like a little silver dinner plate with black bars when it's young. The big thing with African moonies is they're euryhaline-so they'll tolerate freshwater as juveniles, but they really shine long-term in brackish (and can be transitioned toward marine as they mature). Give them a big, open tank and a group, and they turn into nonstop, super fun midwater swimmers.
American shadow goby
Quietula y-cauda
This is a little mudflat goby from California down into the Gulf of California that loves hanging tight to the bottom and vanishing into burrows. The neat tell is that sideways Y-shaped blotch right at the base of the tail, plus the row of dark spots along the side. Its whole vibe is brackish estuary life - calm water, soft substrate, lots of hiding holes.
Banded-tail glassy perchlet
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This is one of those see-through glassy perchlets where you can literally watch the organs shimmer when it turns-super cool in the right lighting. In the wild it hangs around river mouths and mangroves and cruises in groups, so it does best when you keep a little gang of them and give them some open swimming room.
Barbed pipefish
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Urocampus nanus (barbed pipefish) occurs in protected inshore and estuarine habitats among seagrass (Zostera) in the Northwest Pacific (southern Japan and adjacent coasts). Like other syngnathids, males brood eggs in a pouch under the tail and produce fully formed young.
Beach silverside
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This is a little coastal silverside that cruises the shallows in loose groups and flashes like a tiny chrome dart when the light hits it right. In the wild it hangs around beaches, estuaries, and lagoons, picking at small drifting foods in the surf zone. It is cool, but its real "gotcha" is that it is an open-water, salt-tolerant schooling fish that does best in bigger, well-oxygenated setups rather than a typical planted community tank.
Buffon's river-garfish
Zenarchopterus buffonis
This sleek, surface-dwelling halfbeak has a distinct dark stripe along the snout and is typically found at the surface in coastal waters, estuaries, and rivers where it feeds on terrestrial insects. In aquaria it does best with floating/surface foods and a secure cover, and it requires brackish (or marine) conditions long-term. Reproduction is internally fertilized; FishBase lists the species as ovoviviparous.
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Barred mudskipper
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