Nurseryfish
Kurtus gulliveri
The Nurseryfish has a distinctive elongated body, vibrant yellow and blue coloration, and prominent dorsal and anal fins.
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About the Nurseryfish
This is that wild Aussie-PNG river fish where the male carries a bunch of eggs on a little hook on his forehead. It cruises turbid estuaries and lower rivers, munching small fish and shrimp, and it grows way too big for home tanks - we are talking public-aquarium scale. Super cool biology, but not a practical pet for most of us.
Also known as
Quick Facts
Size
63 cm
Temperament
Semi-aggressive
Difficulty
Expert
Min Tank Size
500 gallons
Lifespan
3-4 years
Origin
Northern Australia and southern New Guinea
Diet
Carnivore - small fish, shrimp, crayfish, insect larvae
Water Parameters
20-28°C
7-8
5-25 dGH
Need a heater for this species?
This species needs 20-28°C in a 500 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give them a long, covered tank (120 cm+; 75-125 gal) with open swimming space, dim light, and gentle, even flow; run brackish at SG 1.005-1.010, 27-30 C, pH 7.2-8.2.
- Pre-mix and aerate new saltwater and always match temp and SG on water changes; big weekly changes (30-50%) are fine if you keep the numbers rock steady and oxygen high.
- Use fine sand, rounded wood, and a dark background; skip sharp decor and blasting powerheads, and break up surface ripples with a spray bar or airstones for gas exchange.
- They start eating best on live foods: gut-loaded ghost/river shrimp, mysis, and similar; once they hit hard, blend in frozen and wean slowly, feeding at dusk in low light.
- Tankmates should be calm, brackish, and not nippy or hyper-competitive (think sleeper/knight gobies or larger glassfish); skip scats, monos, archerfish, puffers, and any snack-sized fish.
- Acclimate by slow drip for 1-2 hours with lights off, and move with a container, not a net; they spook hard and can injure themselves on glass.
- Breeding note: males carry eggs on a forehead hook; if you ever see a male with a clump, reduce flow and do not move him, but be realistic that home breeding is extremely rare.
- Big pitfalls are salinity swings and starvation; keep water clean (turbid-looking in nature does not mean dirty), watch for hollow bellies, and act fast if they stop taking food.
Compatibility
Good Tankmates
- Big, peaceful bottom dwellers like violet goby (Gobioides broussonnetii); they sift sand and ignore nurseryfish
- Sturdy sleeper gobies (Butis butis, Eleotris spp.) that hug the bottom and are not hyper
- Green chromides (Etroplus suratensis) in a proper group; steady, non-nippy, handle low-mid brackish
- Similar-size archerfish (Toxotes spp.) in a long tank; they stay up top, just feed separately so Kurtus gets his share
- Large brackish catfish like Colombian sharks (Ariopsis seemanni) if the tank is huge and salinity is on the higher side
Avoid
- Scats and monos (Scatophagus, Monodactylus) - fast, nippy plate-cleaners that will stress a slower Kurtus
- Puffers (figure 8, green spotted) - chronic fin nippers that will pick at the nurseryfish
- Anything bite-size or delicate like mollies, glassfish, bumblebee gobies, or shrimp - they will end up as food
- Big bruisers and outright predators like barramundi, mangrove jack, or large datnoids
Where they come from
Nurseryfish (Kurtus gulliveri) are oddballs from northern Australia and southern New Guinea. They cruise muddy, tidal rivers and mangrove creeks where the water swings between fresh and brackish. The wild story everyone remembers: males carry the egg mass on a bony hook on their forehead. Yes, really.
Setting up their tank
They are big, delicate, and fussy about water quality. Think long tank with open midwater, dim light, and very steady brackish conditions. They spook easily, so keep the layout simple.
- Tank size: 500+ liters (130+ gal), 180 cm/6 ft length is kind to their nerves.
- Salinity: SG 1.005-1.010 (keep it stable).
- Temperature: 25-28 C (77-82 F).
- pH and hardness: pH 7.4-8.0, medium-hard to hard.
- Flow: gentle to moderate with high oxygen. Avoid blasting currents.
- Substrate: fine sand or bare-bottom; they are midwater, but sand keeps things tidy.
- Lighting: low to moderate. A dark background helps them relax.
- Lid: tight-fitting. They jump and also head-butt lids when startled.
Filtration needs to be oversized. Think canister or sump with plenty of bio media and strong surface agitation. They hate ammonia spikes and do poorly in brand-new setups. I run mechanical prefilters to catch silt so the water stays clean without being sparkling bright.
Decor is mostly about line-of-sight breaks along the back and sides so they feel enclosed, but keep the center open. A few sturdy brackish-tolerant plants (Java fern, Anubias) on wood at low salinity can work, or just use inert hardscape. Avoid sharp decor; these fish bruise their snout easily.
Acclimate slowly. I drip acclimate for at least 45-60 minutes and match salinity and temperature before release. Keep the room lights dim for the first day to cut down on panicked dashes.
What to feed them
They are predators that key in on moving food. Most new arrivals will only take live prey. Once they settle, you can wean some individuals to frozen, but pellets are usually a no-go.
- Live foods to start: glass/ghost shrimp, river shrimp, gut-loaded mollies/guppies (quarantine first), live blackworms, small crayfish.
- Frozen options to try later: mysis, prawn pieces, krill, silversides cut to size. Wiggle with tongs if they hesitate.
- Feeding style: dusk or low light, moderate flow so food drifts. Several small feeds for new fish; once stable, 1-2 feeds per day is fine.
Skip feeder goldfish and raw smelt. They are high in thiaminase and often carry parasites. If you use livebearers as feeders, quarantine and gut-load them so your nurseryfish gets real nutrition, not just a chase.
How they behave and who they get along with
They are calm midwater cruisers that spook hard if startled. Not bullies, but anything bite-sized will get eaten. Fast, pushy brackish fish (monos, scats, big archers) can outcompete and stress them.
- Best setup: species-only or a very quiet community.
- Possible tankmates (watch temperament): large sailfin mollies, peaceful gobies that stick to the bottom, calm sleepers/waspfish at low-end brackish.
- Avoid: fin-nippers, high-speed feeders, and anything smaller than their mouth.
They startle at sudden movement. Keep the tank in a low-traffic spot, use a background, and bring lights up gradually on a timer to prevent head-first crashes into glass.
Breeding tips
This is one of those species that fascinates everyone but almost never breeds in home tanks. In the wild, males grow a forehead hook that holds a clump of eggs until they hatch. Captive reports are scarce, and raising larvae is another mountain entirely.
If you want to experiment, you would need a group with both sexes (males have the obvious hook), heavy live feeding, and seasonal cues: several weeks of lower salinity and slightly cooler temps to mimic wet season, then a gradual return to warmer and a bit saltier. Keep the water very clean and disturbance low. Do not handle males by the head; that hook is fragile and injuries get infected fast.
Common problems to watch for
- Refusing food: very common at first. Start with lively shrimp and feed at dusk. Give them quiet time.
- Nose and forehead injuries: caused by panicked dashes. Use soft decor lines, lids, and dim lights.
- Osmotic stress: they do poorly with rapid salinity swings. Change SG slowly, 0.001-0.002 per day.
- Ammonia/nitrite sensitivity: big biofilter, frequent testing, and modest feeding while they settle.
- Parasites and worms: many are wild-caught. Quarantine and consider a deworming plan (e.g., praziquantel, metronidazole) if you see stringy feces or weight loss despite eating.
- Bacterial infections on the head/hook: keep water pristine; treat promptly if you see redness or fuzz.
They are a high-mortality import and not a beginner fish. If a shop specimen is thin, breathing fast, or not tracking live prey, walk away. You save yourself heartache and discourage poor handling upstream.
Similar Species
Other brackish semi-aggressive species you might be interested in.
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).
Bellfish
Johnius fuscolineatus
Johnius fuscolineatus (Bellfish/African bearded croaker) is a small coastal sciaenid from the southwestern/western Indian Ocean (Mozambique, South Africa, Madagascar), occurring in shallow marine waters (reported 0–50 m) and also associated with coastal/estuarine habitats.
Blotched eelpout
Zoarces gillii
Zoarces gillii is a cold-temperate eelpout from the Northwest Pacific that hugs the bottom over sandy-mud inshore areas and even pushes into estuaries. It's got that long, eel-like body and a sneaky, sit-on-the-bottom predator vibe - very much a cool-water, brackish-to-marine oddball rather than a typical tropical aquarium fish.
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.
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.
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.
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.
Barbed pipefish
Urocampus nanus
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
Atherinella blackburni
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.
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