Silverbelly cardinalfish
Jaydia photogaster
Silverbelly cardinalfish exhibit a distinctive silver-grey body with a prominent dark stripe along the side and large, expressive eyes.
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About the Silverbelly cardinalfish
Jaydia photogaster is a small, nocturnal cardinalfish from the western Pacific that hangs around deeper lagoon patch reefs and tends to be seen solo or in little loose groups. The really neat bit is the silvery belly light-organ system (hence the name) and the subtle dusky bars down the sides - it is one of those understated fish that looks way cooler the longer you stare at it.
Also known as
Quick Facts
Size
6 cm (2.36 inches) TL
Temperament
Peaceful
Difficulty
Expert
Min Tank Size
30 gallons
Lifespan
3-6 years
Origin
Western Pacific (Indonesia and Papua New Guinea, also reported Philippines to New Guinea range)
Diet
Carnivore (planktivore/micro-predator) - zooplankton, small crustaceans, fish larvae; in aquaria: small frozen foods and tiny meaty pellets
Water Parameters
22-28°C
8-8.4
8-12 dGH
Need a heater for this species?
This species needs 22-28°C in a 30 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give them a dimmer tank with lots of overhangs and caves - they hang under ledges and get spooked in bright, bare setups.
- Keep salinity steady around 1.025-1.026 and temp 76-79F; they get cranky fast with swings, especially right after shipping.
- They are dusk feeders - target feed after lights go down so faster fish do not steal everything, and watch that the belly actually rounds out.
- Food that works: small meaty stuff like mysis, enriched brine, finely chopped shrimp, and quality pellets once they recognize it; soak foods in vitamins if you are trying to fatten a new one up.
- Do not mix with aggressive dottybacks, big wrasses, or anything that likes to harass at night; they do best with calm reef fish and other cardinals, but add a group at once to cut down on pecking.
- Cover every gap in the lid - they can launch when startled, especially during acclimation or when a larger fish rushes them.
- Breeding note: they are mouthbrooders (male holds the eggs) so if you ever see one refusing food and keeping a tight jaw, do not chase him around - let him hold, and be ready with tiny live foods for the fry.
Compatibility
Good Tankmates
- Other peaceful cardinalfish and small schooling fish that are not jerks - think pajama cardinals, banggai (if not overcrowded), and similar mild-mannered midwater fish. Silverbellies are chill and do best when nobody is trying to prove a point.
- Small, peaceful gobies (watchman gobies, neon gobies, clown gobies). They mostly mind their own business and hang near the rock or sand, and the silverbelly just cruises and grabs food.
- Blennies with a good attitude (tailspot, bicolor in bigger tanks, lawnmower if there is enough algae). Usually they posture a bit but they are not hunting the cardinalfish.
- Peaceful wrasses that are not bullies - like smaller Halichoeres types (yellow coris, melanurus) in the right size tank. They are active but generally leave cardinals alone, and both eat meaty foods well.
- Reef-safe anthias or chromis in a calm setup. Silverbellies are not fast at the dinner bell, so just make sure food actually gets to them (broadcast feed, small pellets, mysis).
- Dwarf angels can work sometimes (flame, coral beauty) if the angel is not a terror. Watch the vibe - a pushy angel can keep a shy cardinal pinned in a corner and outcompete it for food.
Avoid
- Dottybacks (especially orchid or neon dottybacks) - they love to claim a cave and they can absolutely harass a peaceful cardinalfish, particularly in smaller rockwork-heavy tanks.
- Hawkfish (flame hawk, longnose hawk) - not always a guaranteed problem, but they are opportunistic and will bully or eat smaller tank mates if they can fit them in their mouth.
- Aggressive damselfish and mean clowns (maroon clowns, territorial clarkii types, big domino damsels) - they can turn the tank into a no-go zone and the silverbelly will just hide and lose weight.
- Big predators and brutes - groupers, lionfish, larger triggers. Cardinalfish are basically bite-sized for these guys, and even if they do not get eaten, they get stressed nonstop.
Where they come from
Silverbelly cardinalfish (Jaydia photogaster) show up across the Indo-West Pacific, usually around sheltered reefs, rubble, and weedy areas where they can hang in the shade and pick off tiny prey. They are one of those fish that look calm in the store, then you get them home and realize they are picky little nocturnal hunters with opinions.
Setting up their tank
Think dim corners, lots of broken line-of-sight, and places to hover without being in the open. They are not a "centerpiece cruising" fish. If your aquascape is a single open bommie under bright lights, they will act stressed and you will barely see them except at feeding time.
- Tank size: I would not bother under 30 gallons for a single, and 55+ if you want a small group without constant bickering
- Rockwork: caves, overhangs, and tight crevices they can back into (they love vertical cracks)
- Flow: moderate; give them a couple calmer pockets where food can drift by
- Lighting: they do fine under reef lights, but give shaded zones (overhangs, macro, tall rock) so they can chill
These are expert-level mostly because shipping and acclimation can be rough, and a lot of them come in skinny. Plan on a quiet, established tank and be ready to do some "training" onto frozen foods.
I treat them like I would a touchy anthias that happens to be a cardinalfish: stable salinity, stable temperature, and no brand-new tanks. If your tank is still doing that "small swing every day" thing, this is the fish that will punish you for it.
If you can, quarantine them in a dim QT with some PVC elbows and a bit of fake plant cover. Bright bare-bottom QT under white light is where they go off food and spiral.
What to feed them
They are micro-predators. Most new arrivals recognize moving food first, then you can work them onto frozen. Once they are settled, they can be solid eaters, but you have to get them over that first hump.
- Best starters: live or enriched foods like live brine (as a jump-start), live copepods, live blackworms (if you have a safe source), small ghost shrimp for larger individuals
- Frozen staples: mysis (smaller pieces), finely chopped shrimp, calanus, enriched brine (as a mix-in, not the whole diet)
- Pellets: some will take small sinking pellets after a few weeks, but do not count on pellets to save a skinny new fish
Feed after lights have ramped down, or at least target-feed into their cave zone. I use a turkey baster and gently puff food into the shaded areas so it looks like prey drifting by. If you dump food into the open, the faster fish will vacuum it up and your cardinal will act like it "does not eat."
A trick that works: mix frozen mysis with something that really grabs attention (calanus or enriched brine) for a week. Once they are snapping at the mix, slowly reduce the "candy" and leave the mysis.
How they behave and who they get along with
They are generally peaceful, but not helpless. They hover, they posture, and they can be surprisingly territorial about a favorite nook. In small tanks, two that do not like each other will make it obvious.
- Good tankmates: calmer reef fish that will not outcompete them hard at feeding (gobies, blennies, smaller wrasses that are not hyper, many peaceful angels in big tanks)
- Risky tankmates: super-fast feeders (some tangs, big wrasses), aggressive dottybacks, larger hawkfish, and anything that likes to harass cave fish
- Predator warning: if a fish can fit them in its mouth, it eventually will
Do not pair them with really pushy "cave claimers" like dottybacks in a small setup. The cardinal will hide constantly and you will be stuck trying to feed a fish you cannot see.
You can keep more than one, but I have had the best luck either with a single specimen or a small group added at the same time to a bigger, rockier tank. Adding one later to an established territory map tends to go poorly.
Breeding tips
They are mouthbrooders like other cardinalfish, and the male will hold the eggs. In a peaceful tank with steady feeding, you may see the male stop eating and get that "stuffed jaw" look.
- Watch for: a male with a swollen mouth that hangs back and refuses food for days to weeks
- Tank setup help: quiet corners and no constant chasing from tankmates
- If you try to raise fry: you are in live-food land (rotifers/copepods), and you will want a separate rearing setup
Most hobbyists stop at "cool, he is holding." Getting fry past the first stages is possible, but it is a project. If you have never run rotifers before, start there before you try to rear cardinalfish.
Common problems to watch for
The big three with Silverbelly cardinals are shipping stress, starvation (they look fine until they do not), and getting bullied off food. If you stay ahead of those, they are actually pretty steady.
- Refusing food: usually lighting/competition/stress. Dim the area, target-feed, and try smaller moving foods first
- Skinny belly or pinched head: they are losing the race at feeding time or not recognizing the food as food
- Hiding nonstop: often too bright, not enough cover, or tankmates are getting in their space
- Disease after arrival: watch for ich/velvet signs and rapid breathing - they do not handle "wait and see" well
If you suspect velvet (fast breathing, dusting, fish crashes quickly), treat like an emergency. These guys can go from "a little off" to gone fast.
My personal rule: if a new Silverbelly cardinal has not taken something (anything) by day 2-3 in a calm QT, I change tactics immediately. Different food, different time of day, dimmer light, less activity in front of the tank. Waiting them out is how you lose them.
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