Banggai Cardinalfish (Pterapogon kauderni)

Banggai Cardinalfish in brief

The Banggai Cardinalfish (Pterapogon kauderni) is a small marine cardinalfish from one island group in Indonesia. Its silvery body carries bold black vertical bars, one of them running through the eye, and its long, pointed fins are speckled with white. Wikipedia notes that it is the only member of its genus and a popular aquarium fish, and FishBase records a maximum total length of 8.6 cm.

It is also an endangered species. FishBase gives its IUCN status as Endangered and names collection for the aquarium trade as a threat. Wikipedia adds that it is among the relatively few marine fish bred regularly in captivity, although significant numbers are still captured in the wild. Keeping one well, in a mature aquarium and for the long term, is the best way to respect that. If the origin of the fish matters to you, ask us about it before you order.

What makes it different

• It hovers rather than cruises. In the wild, groups of 2 to 60 hover directly above long-spined sea urchins and slip between the spines when threatened.
• The father broods the eggs. The male incubates the eggs until they hatch, and the young stay inside his mouth for a time afterwards.
• Its natural range is tiny. FishBase describes it as apparently restricted to the Banggai Islands, with further records from nearby small islands.
• It stays small. The recorded maximum is 8.6 cm, so it is easily outpaced by larger, faster fish at feeding time.

What you receive

Each purchase is for one live Banggai Cardinalfish, hand-packed by our team and sent with a licensed live-animal courier. Sex is guaranteed only when the selected option explicitly states male or female. This Banggai cardinal fish listing has no sex-guaranteed option. If you are thinking of keeping more than one, read the section on groups and tank mates before deciding how many your aquarium can hold.

Gallery images have been digitally enhanced to improve image quality. Natural colour, pattern, size and maturity can vary between live animals. Some photographs show the fish among green plants and wood. That scenery is not a plan for a marine aquarium; the aquarium planning section explains what to furnish it with instead.

Who it suits

A Banggai Cardinalfish is a good match for a marine aquarium that has matured and holds steady water, has rockwork the fish can hover beside, and is shared with calm fish that will not rush every meal. It also suits a keeper who is happy to plan around an endangered species: deciding in advance how many the tank can hold, and keeping them well for the long term.

It is a poor match for a brand-new tank, a community of fast or aggressive feeders, or a reef stocked mainly with very small shrimps and similar crustaceans, which are close to its natural food. Its modest adult size is an advantage in a home aquarium, provided the companions are chosen with the same care.

Before you buy

• Has the filter matured, with ammonia and nitrite reading zero?
• Have you chosen between a fish-only and a reef aquarium, and set the salinity to match?
• Is there rockwork where the fish can shelter and hover?
• Do you know how many cardinalfish the tank will hold alongside its other residents?
• Will someone be at home on the delivery date to receive the parcel?

To compare other saltwater species, browse our marine fish collection, and use the care sections below to check that your aquarium is ready for this one.

Life around the Banggai Islands

FishBase's species summary describes Pterapogon kauderni as a marine, demersal cardinalfish of the family Apogonidae. It has been recorded from the surface down to 16 m, but usually lives in just 1–2 m of water. The range is remarkably small: FishBase describes it as apparently restricted to the Banggai Islands of Indonesia, with further records from several small islands off eastern Taliabu Island and around Luwuk.

FishBase places that range between roughly 1° and 2° south and 123° and 124° east: a patch of sea so small that collection for the aquarium trade is listed as a threat to the species' survival. That is worth keeping in mind when you decide how many to buy.

Seagrass, sand and sea urchins

It is common around jetties, over silty sand with seagrass (Enhalus acoroides). Its closest partner is the long-spined sea urchin, Diadema setosum. Groups of 2 to 60 fish hover directly above the urchins, and when threatened they retreat among the spines. The youngest fish, at about 2–3 cm standard length, stay closest to the urchins, and juveniles also use anemones for protection.

Feeding after dark

FishBase notes that it probably feeds on small benthic and planktonic crustaceans at night: prey taken from the bottom as well as from the open water. That points to a diet of small crustaceans rather than grazing, which shapes both its aquarium diet and the invertebrates it can safely share a tank with.

What the wild record means for your aquarium

• Refuge matters. Its safety in the wild is a nearby shelter it can drop into. At home, rockwork plays that role, and OATA recommends rock, ideally living rock, as a natural refuge for fish.
• A sandy floor fits. It lives over sand in the wild, and OATA recommends a layer of fine coral sand in marine aquariums.
• Company is normal. It is found in groups, so it is not a strictly solitary species, but the number an aquarium can hold is a separate question covered under tank mates.
• Food should be small and crustacean-based. That follows directly from its recorded wild diet.

Choosing and placing the aquarium

How big?

OATA's guide to setting up a marine aquarium gives a general rule rather than a single number: within reason, buy an aquarium as large as possible, ideally one that can hold your chosen fish once they are fully grown, or be prepared to move to a bigger set-up as they grow. Larger aquariums hold more water, so they are more stable and less susceptible to swings in temperature and pH than small ones.

For a Banggai Cardinalfish, three things set the size: its adult length of up to 8.6 cm, how many you intend to keep, and the other fish and invertebrates that will share the tank. A tank chosen with all three in mind will also be easier to keep stable.

Fish-only or reef?

OATA distinguishes fish-only aquariums from reef aquariums, which also hold invertebrates such as corals. The choice changes the water values you aim for, the water you use and the monitoring you do, so decide early. Both kinds can suit this cardinalfish; the compatibility section explains what to consider with invertebrates.

Where to put the aquarium

OATA advises positioning the aquarium:

• out of direct sunlight and away from sources of heat or draughts;
• on a flat, level surface or stand that can take the weight of a full tank indefinitely;
• away from loud noises, vibrations and sudden movements.

That last point suits a fish whose instinct is to retreat when alarmed. A quiet corner lets it spend its day hovering in view rather than hiding.

Water movement

OATA notes that different species prefer different water types and flow rates. A fish whose habit is to hover in one place near cover is easiest to keep, and to watch, where the flow lets it hold position comfortably, so keep strong jets away from the rockwork it favours while still moving water through the whole aquarium for the filter and skimmer.

Rock, sand and plants

OATA recommends rockwork, ideally living rock of some description, as a natural refuge for fish and a place to site corals if you keep them, along with a layer of fine coral sand. Build the rock so there are sheltered spots with open water in front of them, where the cardinalfish can hover close to cover. OATA also notes that live plants are generally not kept in marine aquariums, apart from specialist set-ups such as refugiums or mangroves.

Salt water, filtration and maturing

Making the salt water

OATA recommends reverse osmosis (RO) water for marine aquariums, because it has been filtered to remove impurities, and describes it as essential if you want to keep invertebrates such as corals. RO water can be bought ready-salted or as freshwater to mix at home. If you mix it yourself, dissolve specialised aquarium salt, never table salt, following the manufacturer's instructions; water flow from a powerhead and warmth from the heater speed the process up.

For the first fill this can be done inside the aquarium. After that, OATA advises mixing and heating water for water changes in a separate container, so it is ready at the right salinity and temperature before it goes in. Coral sand can be rinsed in RO water and added once the salt is in.

Letting the system settle

Once the aquarium is filled, at the correct salinity and temperature, the rest of the equipment can be switched on. OATA suggests leaving it for 24 to 48 hours so any salt fully dissolves, the temperature stabilises and you can confirm everything works. A protein skimmer may not remove any waste until livestock is added, and recommendations on when to start skimming vary, so ask us if you are unsure. That short settling period is only the start: the filter still has to mature before fish go in.

Maturing the filter

The RSPCA's advice on fish environments sets out why. Fish release ammonia, which is toxic. In a working biological filter, beneficial bacteria convert it to nitrite, also toxic, and then to nitrate, which is safer. OATA adds that this bacterial population has to grow every time more fish are added and feeding increases. Overstocking, or stocking too quickly, leaves too few bacteria to cope, and the resulting rise in ammonia and nitrite is known as new tank syndrome.

Water changes

Because new salt water is mixed and heated in a separate container, you can check it before it goes in. Bring it to the aquarium's temperature, confirm its salinity with the hydrometer or refractometer, and only then make the change. Matching the two keeps the stability that larger volumes are chosen for, rather than undoing it with every water change.

The kit you need

• A hydrometer or refractometer, which OATA calls one of the most important pieces of equipment, to monitor salinity
• Test kits to measure water quality regularly, starting with ammonia and nitrite
• A heater and a powerhead or other source of water movement
• A separate container for mixing and heating new salt water
• Fine coral sand and rockwork, ideally living rock

Water values for fish-only and reef tanks

OATA publishes two sets of home-aquarium values: one for fish-only systems and one for aquariums that also hold invertebrates. They are broad marine guidance rather than figures measured for this species, so pick the column that matches your system and keep the water steady within it.

A simple target for this fish

Temperature and pH are where the two sets overlap. A steady 24–26°C with pH 8.0–8.2 sits inside both, so those are sensible targets whichever kind of aquarium the cardinalfish lives in. Salinity is different: the fish-only and invertebrate bands do not overlap, so set it for the most demanding animals in your tank.

Stability over precision

OATA's point about larger aquariums, that they are less susceptible to variations in temperature and pH, is the practical heart of marine care. Choose your targets inside the ranges above and keep the water there: a steady reading day after day matters more than chasing an exact number.

Reef extras

If you keep hard corals, OATA adds that calcium and magnesium should also be monitored, and its separate coral care sheets cover them. The lower nitrate and phosphate limits for invertebrate systems are another reason to feed carefully and keep stocking modest in a reef.

Testing

Check salinity with your hydrometer or refractometer and test ammonia and nitrite regularly, adding nitrate and the reef measures if invertebrates share the tank. Any ammonia or nitrite reading above zero means the filter is not keeping up, and it needs attention before more livestock is added.

Feeding a Banggai Cardinalfish

The starting point is the wild record. FishBase notes that the Banggai Cardinalfish probably feeds on small benthic and planktonic crustaceans at night. Mysis shrimp and brine shrimp are small crustaceans themselves, so frozen foods of that kind are the closest match to its natural diet and the obvious base for its menu.

Portion size and waste

Feed modest amounts, and watch what happens to the food. Anything the fish does not eat breaks down in the aquarium and adds to the waste the filter bacteria must process; OATA links rising feeding directly to the load on a maturing filter. In a reef, the tighter nitrate and phosphate limits make that restraint even more important.

The first feeds

Watch the new fish closely at each feed during its first days. Note whether it rises to take food, how readily it eats and whether it seems more interested at some times of day than others; its wild feeding probably happens after dark. A fish that feeds steadily is settling in. One that ignores food should prompt a water test straight away, and a message to us if the readings are fine.

Working with its natural rhythm

Because its wild feeding probably happens at night, a fish that seems hesitant at a morning feed may be keener later in the day. Try offering food at different times during the first weeks and settle on the routine it responds to best, keeping each portion modest.

Feeding in company

A hovering fish of up to 8.6 cm is easily beaten to food by faster, bolder tank mates. Offer food where the cardinalfish is waiting near its shelter, and check that it is actually eating rather than watching others take everything. If it is losing out at every feed, the mix of fish needs rethinking.

Delivery, unpacking and the first days

Our team hand-bags your cardinalfish in pure oxygen and packs it in an insulated poly box, adding a heat pack when the weather calls for it. A licensed live-animal courier carries the parcel, and we email you the tracking number and your confirmed delivery date. Because live fish cannot be left unattended, someone must be at the address to receive them.

Before it arrives

OATA's advice is to check first that the new fish is compatible with those you already keep and that ammonia and nitrite are both at zero. Test in the days before delivery, confirm the salinity and temperature, and make sure the rockwork gives the newcomer somewhere to shelter straight away.

Unpacking and acclimatising

1. Before the parcel is opened, begin a continuous unboxing video with the sealed outer box in shot.
2. Keep recording in the same take as you open it, until the fish is visible inside its sealed bag.
3. Float the bag in your aquarium for 20–30 minutes so the fish acclimatises slowly.
4. Let the fish out into the aquarium, and do not pour the bag water in with it.
5. If anything has gone wrong, message us the same day, WhatsApp being quickest, with your order number and the unboxing video, and we will arrange a replacement or refund.

The Live Arrival Guarantee relies on three things: someone at the address to receive the parcel, the parcel opened and inspected on the day it arrives, and a continuous unboxing video that starts with the parcel still sealed. Read the full terms on our delivery and Live Arrival Guarantee page.

The first days

Expect a new Banggai Cardinalfish to stay close to cover at first; retreating to shelter is how it responds to threats in the wild. Keep the room around the aquarium calm, watch it at each feed, and hold off adding other new fish until it is settled and eating, so the filter bacteria are not asked to cope with several arrivals at once.

OATA notes that fish are easily stressed by bright lights, extreme temperatures, noise and movement. Those are worth keeping to a minimum for the first days too: keep people and pets from crowding the glass, avoid working in the aquarium unless you need to, and let the fish learn its surroundings from its chosen shelter.

Breeding biology and conservation

A mouthbrooding father

FishBase records that the male incubates the eggs until they hatch. The eggs are large, about 2.5 mm in diameter, and the young remain in his mouth cavity for an undetermined period after hatching. Newly hatched larvae have no planktonic stage, so the young do not spend a drifting larval phase in open water.

FishBase notes that the species has been reared in captivity, and Wikipedia describes it as among the relatively few marine fish bred regularly in captivity. This listing sells single fish and the sex of each one is not selected, so it is not set up to supply a breeding pair.

Why it is endangered

FishBase lists the Banggai Cardinalfish as Endangered and names collection for the aquarium trade as a threat to it. Wikipedia adds the detrimental impact of humans on its environment and certain fatal diseases, noting that iridovirus diseases are a significant cause of mortality.

Keeping one responsibly

• Buy only when your aquarium is mature, stable and ready for it.
• Plan for its whole life: an adult length of 8.6 cm, a group-living nature and steady marine water.
• Watch new fish closely in their first weeks and act quickly on any change in feeding or behaviour.
• Never release aquarium fish into the wild.

Groups and tank mates

How many to keep

Wild Banggai Cardinalfish live in groups of 2 to 60, hovering together above sea urchins. An aquarium is a different matter. OATA's marine stocking guidance states that it is not possible to say exactly how many fish an aquarium can hold, because body size, species needs, water values and compatibility vary so widely, and that territorial behaviour in many marine fish reduces the number further.

So the right number depends on your aquarium, not on a rule of thumb. Each purchase supplies one fish; tell us your tank's volume and current residents before buying several, and we will help you settle on a number that leaves room to grow and space for everyone to find shelter.

If you plan a group, remember that several fish arriving together are still one large addition for the filter to absorb. OATA's advice to increase fish numbers slowly applies here as well, so make sure the biological filtration is well established before a group goes in, and hold back other new livestock until they have settled.

Choosing companions

OATA notes that some marine species need to be kept in shoals, while others are territorial or aggressive and will not live together peacefully, and it advises checking that any new fish is compatible with those you already keep. For this cardinalfish, the wild picture is a slow, hovering fish whose defence is to retreat to shelter. Build the community around that:

• calm fish that will leave a hovering neighbour alone;
• tank mates that will not beat it to every scrap of food;
• enough rockwork that every fish can claim cover without crowding the cardinalfish out of its spot.

Fish to leave out

• Aggressive or strongly territorial species that could harass a slow fish
• Fast, boisterous feeders that would leave it hungry
• Any fish large enough to see an 8.6 cm cardinalfish as food

Planning checklist

Add new fish gradually, one change at a time, and watch feeding times closely after each addition.

Invertebrates and reef aquariums

In the wild the Banggai Cardinalfish lives among seagrass and long-spined sea urchins, and its juveniles also shelter in anemones. Its recorded food is small benthic and planktonic crustaceans; corals are not part of that recorded diet.

What to consider in a reef

• Very small crustaceans are its natural prey, so tiny shrimps and similar animals may be eaten.
• Water standards rise. OATA's invertebrate values set tighter nitrate and phosphate limits, a higher salinity band and carbonate hardness of 8–12 dKH, and RO water becomes essential.
• Hard corals bring calcium and magnesium into the routine as well.

Sea urchins and anemones

Its wild partnership with long-spined sea urchins, and the way juveniles shelter in anemones, is one of the most interesting things about this fish. An urchin or anemone is not needed for it to settle, though; rockwork provides the refuge. If you are thinking of adding either, treat it as a separate animal with care needs of its own and talk to us first.

Fish-only with living rock

A fish-only aquarium with plenty of living rock is the simpler home. It avoids the question of small crustaceans, allows OATA's wider fish-only ranges and still gives the cardinalfish the refuge it relies on. If you choose a reef instead, set the aquarium up for the invertebrates first and add the fish once the water is stable at the tighter values.

Common questions

How big does a Banggai Cardinalfish grow?

FishBase records a maximum total length of 8.6 cm. That is the adult figure to plan around, whatever size the fish is when it arrives.

What size aquarium does it need?

OATA's marine guidance is to buy as large an aquarium as is reasonably possible, sized for your fish once they are fully grown, because larger volumes are more stable and less susceptible to swings in temperature and pH. Size it for the number of cardinalfish you plan to keep and everything else that will share the tank.

How many Banggai Cardinalfish can be kept together?

In the wild they hover in groups of 2 to 60 fish. OATA points out that no one can say exactly how many fish a particular aquarium can hold, and that territorial behaviour in many marine fish reduces the number, so tell us your tank size and current fish and we will help you decide.

Is it a good fish for a new marine aquarium?

Add it only once the filter has matured and ammonia and nitrite read zero. OATA explains that stocking too quickly can cause new tank syndrome, when there are not enough filter bacteria to cope with the extra waste, so build up any marine tank slowly and bring this fish in once the system is stable.

What does a Banggai Cardinalfish eat?

FishBase records that it probably feeds on small benthic and planktonic crustaceans at night. Frozen crustacean foods such as mysis shrimp and brine shrimp are the closest match to that natural diet; feed modest amounts so uneaten food does not add to the waste in the aquarium.

What temperature and pH does it need?

OATA's broad marine guidance gives 24–27°C for fish-only aquariums and 24–26°C where invertebrates are kept, with pH 8.0–8.2 in both, zero ammonia and zero nitrite. A steady 24–26°C and pH 8.0–8.2 suits either kind of set-up.

Is a Banggai Cardinalfish aggressive?

Its wild behaviour is to hover in groups near cover and retreat among sea urchin spines when threatened. Plan its community around that: calm companions, rockwork to shelter in, and no fish likely to harass a slow, hovering species.

What other animals can it live with?

In the wild it lives among seagrass and long-spined sea urchins, and juveniles also shelter in anemones. In an aquarium, choose calm fish and treat very small crustaceans with caution, because small crustaceans are its natural food.

How is a Banggai Cardinalfish delivered alive in the UK?

Our team hand-bags it in pure oxygen and packs it in an insulated poly box, adding a heat pack when the weather calls for it, and a licensed live-animal courier delivers it after we email your tracking number and confirmed delivery date. Be at home to receive it, record a continuous unboxing video that begins with the parcel still sealed, then float the bag for 20–30 minutes before letting the fish out.

Sources

• FishBase: Pterapogon kauderni species summary: family, depth, range, habitat, sea urchin association, wild diet, breeding biology, maximum length and IUCN status
• Wikipedia: Banggai cardinalfish: genus, aquarium popularity, breeding in captivity and threats including iridovirus disease
• OATA: How to set up and look after a marine tank: aquarium size and position, salt water, maturing, fish-only and invertebrate water values, stocking and adding livestock
• RSPCA: Fish environment: filtration and the nitrogen cycle
• Tropical Fish Co delivery and Live Arrival Guarantee page: packing, courier, acclimatisation and claims, linked in the arrival section