A look at the unique cardinalfishes for marine aquarists wanting something a little bit different for their saltwater aquarium.
Cardinalfish, or cardinals for short, are a wonderful group of fishes. No, not the bright blue freshwater tetra we all know and love, Paracheirodon axelrodi. We are focusing a family of fishes called Apogonidae. While some of them occur in freshwater and brackish conditions, the ones we are looking at today all live in the sea.
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Why choose cardinalfish for marine aquariums?
The cardinals you are likely to encounter in your local marine store all make great options for reef aquariums. They stay at manageable sizes, with the bigger options maxing out at around 12cm (4.8") and are mostly reef safe. But my favourite thing about them is their compatibility with each other.
Many reef aquariums feature one of each fish, a sort of pick and mix style to stocking an aquarium. Chromis and other damsels may sometimes be stocked in larger groups, but they often slowly dwindle in numbers. Meanwhile, the active anthias are another social fish but are only suitable for much larger saltwater tanks. This is where the cardinals come into play.
Cardinals are relatively peaceful towards one another, they typically like the company of their own kind. Plus, they are suitable for more modest aquariums thanks to their smaller size and less active lifestyle. Plus, unlike chromis and damselfish, they are unlikely to pick off the weakest individual. Aggression only ever shows if a pair forms and in good sized reef tanks it is usually not a problem.
The one we all know: Banggai cardinalfish
This contrasting black and white fish is instantly recognisable to anyone that has browsed in a marine store. The Banggai cardinal (Pterapogon kauderni) is one of the few popular marine fish that doesn't rely on bright colours. They have a limited range in the wild, restricted to the waters around the Banggai island in Indonesia.
Their restricted distribution, and demand from the hobby, has caused their population to come under threat. Luckily, there is no reason to buy wild caught Banggais these days as captive breeding is possible and has been occurring for a long time.
A pair can work well in nano reef tanks as small as 100 litres (22 gal). Try to pick out pairs that have formed in the shop tanks rather than buying a group for smaller aquariums. Pairs will pick on the others in a group once formed and in nano tanks they do not have space to retreat. For larger aquariums go for a good sized group to spread any aggression.
Which is the best cardinalfish for a reef tank?
People often overlook the other species of cardinals in the hobby. Perhaps it is because you just don't see them as often in the shops. However, they are equally as wonderful.
So, while you may see the Banggai cardinal and think "sold, that's the one I want", let's quickly look at some of the others. You may be surprised at what else is available and each one has their own 'unique selling points'.
All the cardinals will eat anything that fits in their mouth. Therefore, it is worth remembering that small ornamental shrimp and nano gobies could be at risk with some of the larger options. Always double check your stock compatibility before buying.
Related article: Characterful blennies for your reef tank.
Pyjama cardinalfish
The pyjama cardinal (Sphaeramia nematoptera) has perhaps the best of both worlds. They still have the contrasting patterns like the Banggai but they also display beautiful colours. A bold back line, red-orange spots and a golden head with a bright red eye, this is a pretty fish. Their patterns and colours do fade as they age though, with old fish becoming much more drab.
Pyjama cardinals are great, hardy, beginner marine fish. They do typically get a little larger than the Banggais so you will need a slightly more spacious aquarium for a group of them. They are also probably the second most common and popular in the hobby, and you can certainly see why. So sourcing them shouldn't be too much of an issue.
Ghost cardinalfish
At the other end of the spectrum, ghost cardinals (Zoramia leptacantha) have less obvious beauty. Predominantly they display a silvery white base. However, the electric blue and orange streaks around the head add a subtle interest.
They stay smaller, reaching 6cm (2.4") in length and are less likely to prey on small shrimps than the above relatives. Opt for a group and they won't disappoint, forming loose aggregations close to the cover of the rocks and corals.
Red-spot cardinalfish
The smallest option, the red-spot cardinal (Ostorhinchus parvulus), offers a shoaling fish for smaller tanks. A maximum size of just 4cm (1.6") means they are unlikely to be a threat to small tank mates too. The red spot on the caudal peduncle that give them their name is striking when in a group. It complements a silvery body with a black and blue lateral stipe.
These fish have a reputation of being sensitive and randomly dying in the hobby. This seems to be down to collection and shipping methods, with fish needing time to settle and feed during each step. Shop around and find a group that look well fed, settled and eagerly accept food in the shop.
Orange striped cardinalfish
This is another gorgeous species, the orange striped cardinal (Ostorhinchus cyanosoma) unsurprisingly has bright orange stripes. A bluish silver base colour works together with the bold orange to create a visually striking fish.
They reach a similar size to the pyjama cardinals, perhaps staying slightly smaller. Therefore, a good size reef is needed to keep the numbers required for these fish to feel safe.
Related article: Back to saltwater: starting simple with beginner corals.
Tips to succeed with cardinalfish
- To successfully keep cardinals in a group, your best bet is to buy them all together. Adding a male to a tank with a dominant male already present can cause disputes between them.
- Decorate the aquarium with plenty of rock work, including lots of overhangs and ledges. These fish require plenty of cover to feel safe, the more hidey-holes you provide, the more you will see them.
- Cardinals are most active during the evening and night. Set a good period of blue moon light in the evenings to be able to enjoy your fish when they are out more.
- Feed a varied diet including live and frozen food meaty foods like mysis and brine shrimp along with prepared diets like marine flake food.
- Cardinals are peaceful and can be outcompeted by boisterous tank mates. Avoid aggressive fish that patrol the rocks, like dottybacks, so that your cardinals don't feel stressed.
- The above list of species is just a handful of what's available, spend some time looking more closely at cardinals to see if any of the others take your fancy.
Potential breeding project
Cardinals are a mouth brooding species, with males holding eggs in their mouth until they hatch. Many of the species have been successfully bred in captivity and they can make an excellent marine breeding project.
You will need a separate tank to rear the fry in. The methods for separating the fry from the parents vary, but the best option is keeping the breeding pair in a spawning tank.
Otherwise, you will need plenty of patience to try and catch the male from the display reef before the eggs hatch. Other alternatives include using fake sea urchins for baby Banggais to congregate around. You can then capture and move the fry with ease, if they manage to avoid the hungry mouths of the tank mates.