Knight Goby
Stigmatogobius sadanundio
Also known as: Grey Knight Goby, Hi-Fin Knight Goby
Knight gobies are those chunky, spotty "estuary" gobies that perch on the bottom, scoot between caves, and then suddenly dash out like little predators. They're super fun to watch because they're territorial in a goby way (lots of posturing) and they'll even breed in caves when they're happy. They do best long-term when you treat them like an estuary fish: hard, alkaline water and (often) a bit of salt.
Knight Gobies exhibit a robust, elongated body with a mottled brown and tan coloration, complemented by striking blue spots and a prominent dorsal fin.
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Quick Facts
Size
9 cm SL (about 3.5 inches)
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
30 gallons
Lifespan
5-7 years
Origin
South & Southeast Asia
Diet
Carnivore/mostly meaty foods – small fish and invertebrates in nature; in tanks: frozen/live foods plus sinking meaty pellets
Water Parameters
20-26°C
7-8.5
9-19 dGH
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Calculate heater sizeCare Notes
- They're often kept best in lightly brackish water; many sources recommend around SG 1.003-1.008 (commonly ~1.005). In the wild they're also reported from mostly freshwater/estuarine tidal zones, so avoid rapid salinity swings and base the long-term plan on the specific stock/source.
- Give them a sandy bottom with lots of cover (rocks, driftwood, caves, plants that tolerate brackish like Java fern); they're sit-and-wait hunters and hate a bare tank.
- They get chunky and territorial-think 30+ gallons if you want more than one, and add multiple caves so the boss fish can't guard the whole tank.
- Feeding is easy if you lean meaty: frozen bloodworms, brine shrimp, mysis, chopped shrimp; most ignore flakes at first, so use a turkey baster/tongs to drop food right in front of them.
- Tankmates: go with other brackish fish that aren't tiny (bumblebee gobies, mollies, figure-8 puffers only with caution); avoid neon-sized fish and shrimp because they'll get eaten.
- Watch the nitrite/nitrate-gobies don't love "old tank funk," and brackish setups sometimes trick people into slacking on water changes; keep it clean and well-filtered with decent flow.
- Breeding is cave-based: a male will claim a cave and guard eggs; if you actually want fry, move the adults or the cave to a separate rearing tank because the babies are tiny and disappear fast.
Compatibility
Good Tankmates
- Mollies (especially bigger/sailfin types) - tough, brackish-friendly, and fast enough to avoid the knight goby's "I own this corner" attitude. They also stay up in the water column more.
- Monos (Mono argentus / Mono sebae) - schooling mid/upper swimmers that don't care about a goby on the bottom. Best when they're not tiny and the tank has swimming room.
- Scats (Scatophagus argus) - solid brackish fish with armor vibes. They're bold and quick, so the knight goby usually can't bully them. Again: don't mix with tiny juveniles in a cramped tank.
- Knight goby with another knight goby only if you've got space, sight breaks, and you're cool watching some posturing. A male+female (or a bigger tank with multiple hides) goes way smoother than two males in a small setup.
- Figure-8 puffer (only in a roomy brackish tank, well-fed, lots of decor) - sometimes works because they're quick and not easy targets, but it's very "know your puffer" and have a backup plan.
- Archerfish (with size/space considerations) - commonly listed as a potential tankmate in brackish setups; ensure adequate tank size and avoid mixing with tiny knight gobies.
Avoid
- Bumblebee gobies (Brachygobius spp.) - often discouraged due to knight goby territoriality toward other bottom-dwellers; mixing bottom gobies can lead to harassment unless the system is very large and carefully structured.
- Small, bite-sized fish like guppy-sized livebearers, tiny gobies, or little community fish - knight gobies are ambush predators and they will absolutely try to inhale anything that fits in their mouth.
- Slow fish with fancy fins (bettas, fancy guppies, long-finned anything) - they get stressed, nipped, or just constantly harassed because they can't get out of the way.
1) Where they come from
Knight gobies come from India and nearby areas, hanging out in estuaries and mangrove-ish waterways where fresh and salt mix. That “in-between” water is why they’re so much happier in brackish than in straight freshwater long-term.
If you’ve only ever kept freshwater gobies, this one’s a little different: think "small predator in brackish" more than "cute community bottom fish."
2) Setting up their tank
Give them floor space and hiding spots. They’re bottom-oriented and they like to claim a patch of sand with a cave, so a long tank beats a tall one.
- Tank size: I’d start at 20 long for one, 30+ if you want multiple (they get chunky and territorial).
- Substrate: sand or very smooth fine gravel—these guys sit, scoot, and dig a bit.
- Decor: rock piles, driftwood, and caves (PVC elbows work, but rocks look nicer). Make more hides than fish.
- Filtration: they’re messy eaters, so use a decent filter and don’t skip water changes.
- Flow: moderate is fine; they like calmer spots behind hardscape.
For brackish, I’ve had the best luck keeping them around low-to-mid brackish rather than barely-salted water. Mix salt with a hydrometer or refractometer, not by guesswork. Stability beats chasing a magic number.
Use marine salt mix (not aquarium “tonic” salt). And pre-mix your brackish water in a bucket with a small pump or airstone so the salt fully dissolves before it hits the tank.
They’re escape artists. A tight lid matters, especially if you leave any gaps around wires or airline tubing.
3) What to feed them
Knight gobies are little ambush predators. Mine always did best on meaty foods and acted like pellets were optional unless they were really hungry.
- Great staples: frozen bloodworms, mysis, brine shrimp (better as a treat), chopped prawn/shrimp, krill pieces.
- Live foods (if you can): blackworms, live brine, small earthworm bits—awesome for conditioning.
- Pellets: some learn sinking carnivore pellets, but don’t count on it right away.
Target feed with tongs or a turkey baster. They’re slow-ish and can get outcompeted, plus you’ll waste less food (and brackish tanks get funky fast if you overfeed).
4) Behavior and tankmates
They’ve got that classic goby personality: curious, a bit grumpy, and very "this is my cave." Most problems people have are from treating them like peaceful community fish.
They’ll absolutely eat anything that fits in their mouth. Small fish and tiny shrimp are basically snacks. With other bottom dwellers, it can turn into a turf war.
- Good tankmates: brackish-tolerant fish that aren’t tiny and don’t live on the bottom (larger mollies, some monos/scats when size fits, certain brackish puffers are a bad idea—too nippy).
- Risky: other gobies, small livebearers, small tetras/rasboras (also not brackish anyway), shrimp.
- Best setup honestly: species tank or a carefully chosen brackish group where the goby isn’t the smallest fish.
Fin-nippers stress them out, and stressed knight gobies stop eating. If you see them hiding constantly and not coming out for food, rethink the roommates.
5) Breeding tips
Breeding is doable, but it’s not a “free fry every month” fish for most people. The adults will usually pick a cave and spawn on the roof/walls. The male tends to guard the spot and act extra tough.
- Set the stage: multiple caves with narrow entrances (they love snug hideouts).
- Conditioning: heavy meaty foods for a couple weeks and keep the water really clean.
- After spawning: expect guarding behavior—other fish will get chased hard.
Raising the fry is the tricky part. You’ll need very small foods at first (think infusoria/microworms/baby brine depending on fry size) and a plan to keep water quality up without blasting them with flow.
6) Common problems to watch for
- Kept in freshwater long-term: they may survive for a while, but they tend to get run-down and more disease-prone.
- Not eating: usually stress (tankmates, too bright/open, no caves) or the food isn’t meaty enough.
- Overfeeding/dirty substrate: they’re messy and brackish tanks can swing fast—ammonia/nitrite spikes show up as lethargy and rapid breathing.
- Aggression injuries: torn fins and bite marks happen if the tank is too small or hides are limited.
- Ich/velvet after shipping: very common with wild-caught brackish fish—quarantine helps a lot.
Quarantine them if you can, and don’t rush acclimation. I drip acclimate for salinity changes, keep the lights low the first day, and offer frozen food once they’ve had a few hours to settle.
Similar Species
Other brackish semi-aggressive species you might be interested in.
American flagfish
Jordanella floridae
Jordanella floridae is that little Florida native with the red-and-cream striping that really does look like a tiny flag once a male colors up. They graze algae like champs (especially stringy/hair algae), but they have a bit of attitude - give them plants and space so the bossy behavior stays manageable. Bonus: the male guards the eggs and will actively fan them, which is pretty fun to watch.
Banded Archerfish
Toxotes jaculatrix
This is the fish that literally spits jets of water to knock insects off branches-watching one "take aim" is unreal. They're super aware of what's going on outside the tank and will even learn to beg and snipe food from the surface once they settle in. Give them height and some open swimming room and they act like little aquatic sharpshooters.
Barred mudskipper
Periophthalmus argentilineatus
This is one of those classic "walks around like it owns the place" mudskippers-big goofy eyes, climbs, hops, and spends a ton of time out on the mud when it's humid. In the wild it lives on intertidal mangrove/nipa mudflats and even shuttles between little pools and open air, hunting worms, insects, and small crustaceans. It's super fun to watch, but it really wants a brackish paludarium setup (not a normal aquarium).
Bumblebee goby
Brachygobius doriae
Brachygobius doriae is one of the classic "bumblebee gobies" - tiny, bottom-hugging little characters that perch on rocks and sand and stare at you like they own the place. They're at their best in a calm setup with lots of caves and leaf litter, and they really shine once you get them eating frozen/live foods reliably (they're slow, picky eaters). Also: they're one of the species that gets mislabeled a lot in shops, so it's super common to see them sold under the wrong bumblebee-goby name.
Bumblebee goby (Bumblebee fish)
Brachygobius xanthozonus
This is that tiny little goby with the bold black-and-yellow bands that likes to perch on the bottom and stare back at you like it owns the place. It's happiest in lightly brackish water with lots of little caves and sight-breaks, and it's one of those fish that often refuses flakes-frozen/live meaty foods usually flip the "yes, I will eat" switch.
Colombian shark catfish
Ariopsis seemanni
This is that slick silver "shark-looking" catfish with the black fins and white tips that cruises around like it owns the place. The big gotcha is it's not a true freshwater community fish long-term-juveniles show up in shops as "freshwater," but as it grows it really wants brackish and eventually full marine conditions, plus a lot of swimming room.
More to Explore
Discover more brackish species.
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.
Atlantic Mudskipper
Periophthalmus barbarus
This is that wild little amphibious goby that straight-up climbs around on land like it forgot it was a fish. They've got big googly eyes, tons of personality, and they'll perch, hop, and patrol their territory-honestly more like a tiny crabby lizard than a "regular" aquarium fish.
Banded-tail glassy perchlet
Ambassis urotaenia
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.
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Elongate mudskipper (pointed-tailed goby)
Pseudapocryptes elongatus (syn. Pseudapocryptes lanceolatus)
This is that super-cool "mudskipper-ish" goby that mostly stays in the water, but will park itself in the shallows and periscope its eyes above the surface like it's keeping watch. It's an obligate air-breather from tidal rivers/estuaries, so it really appreciates shallow, brackish setups with soft mud/sand and gentle flow-more of a mangrove vibe than a typical community tank.
Eyespot pufferfish (Figure-8 puffer)
Dichotomyctere ocellatus
This is the little "figure-8" puffer with the yellow-green squiggles and the two bold eyespots near the tail-tons of personality in a small body. They're basically snail-hunting machines with a curious, interactive vibe, but they can be spicy with their own kind, so you plan the tank around that.
Fat sleeper
Dormitator maculatus
Dormitator maculatus is that chunky "sleeper goby" type fish with the bulldog head and the attitude of a little vacuum cleaner-always sifting and nosing around the bottom. It'll do freshwater or brackish and it can get way bigger than most people expect, so it's one of those fish that's awesome... as long as you plan the tank around the adult size, not the baby you bought.
Looking for other species?