Pajama Cardinalfish (Sphaeramia Nematoptera)

pajama cardinalfish

Last updated on July 24th, 2022 at 05:35 am

The pajama cardinalfish (Sphaeramia nematoptera) is one of the most popular marine aquarium fish species, and with its stunning colors and unusual sleeping habits, it’s easy to see why! However, these fishes are typically rather delicate and can be difficult to care for, especially if you don’t know what you’re doing.

It’s tempting to grab any fish that you think looks cute at the pet store, especially if they’re small and seem easy to care for. But just because something looks like it won’t be hard to take care of doesn’t mean that it won’t be, so here are some tips to help you with your new pajama cardinalfish (Sphaeramia nematoptera). These tips can also be applied to other fish from this family if you prefer not to have your pet swim by itself all day long.

The pajama cardinalfish is a very popular saltwater fish and reef tank resident, largely due to its interesting coloration and hardiness.

Origin and description

The pajama cardinalfish, Sphaeramia nematopterus, is an attractive saltwater fish that has been popular in aquariums since it was discovered. The fish was originally discovered near Japan and Korea in Japanese waters, but they have now spread out over all of Japan and southern and southeastern Asia as well as Hawaii.

One reason for their popularity with aquarists is that they are one of few species of cardinalfishes found in shallow waters. They can be found living at depths from 1-25 meters deep, although generally occurring between 4-10 meters deep. They typically inhabit soft bottoms such as mud or sand or areas where there is rubble from rocks that have broken up on reefs.

They generally spend time hunting around buried debris such as dead corals or dead coral branches looking for small invertebrates such as shrimps, mollusks, worms, and tiny crustaceans called amphipods.

Species profile

pajama cardinalfish

Sphaeramia nematoptera was first described by Carl Linnaeus in 1758 based on material from Suriname where it is natively found at depths of 15–40m (50–130 ft) in shallow-water habitats. They are oviparous and feed on invertebrates.

They belong to the family of Apogonidae and have small black spots along their body which gives them a characteristic appearance. A male fish may reach 6 cm in length while females tend to be larger reaching 8 cm in length.

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The average lifespan of pajama cardinalfish is expected to be up to 7 years with proper care. In captivity, these fish can live anywhere from 3 months to 7 years with an average life span closer to 5 years in captivity.

Scientific name

The scientific name of the pajama cardinalfish is Sphaeramia nematoptera


In nature, Sphaeramia nematoptera live in groups with other Sphaeramia or in burrows near coral reefs. Because of their relatively large size, at least 30 gallons is recommended for your fish tank. They are also nocturnal, so it’s best if you keep lights off during their active hours and allow them to adjust to their new home before turning any lights on at all.

Pajama cardinalfish size

This species can grow to a maximum size of 3 inches (8 cm) in length.

Pajama cardinal tank size

The minimum recommended tank size for this fish is 30 gallons (114 liters)

Tank Requirements

The pajama cardinalfish is considered one of, if not the most, beautiful fish in an aquarium set up. These fish prefer hard water and live in schools during their natural habitat. Be sure that you have enough room in your tank for multiple pajama cardinalfish, because unlike many of its relatives (such as jewel fish), it does not thrive alone or with just one or two companions.

It needs at least five other individuals to feel comfortable and happy within an aquarium set up. You will need to keep them away from aggressive species like lionfish because they can pose a serious threat to your fish. Other than providing your fish a good living environment, there are other things you can do to ensure that they stay healthy while they’re in captivity.

The pajama cardinalfish is hardy and adaptable in terms of its water requirements. Be sure to provide it with plenty of space, it’s an active swimmer and will do best in an aquarium with ample room. The water temperature should stay between 74 degrees Fahrenheit and 79 degrees Fahrenheit, while salinity should be kept at 1.020 or less.

Water flow should be moderate, as extremely high flows can cause injury to even tough fish like Sphaeramia nematoptera. Your pajama cardinalfish will need proper filtration too, use a softening filter that effectively removes particulate matter but won’t damage delicate coral frags and invertebrates.

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Pajama cardinalfish tank mates

While pajama cardinalfish has beautiful coloring, they are not aggressive. They should be kept with others of their own kind. The best tank mates for pajama cardinalfish are other docile, small fish like neon gobies and pencilfish.

They may also be compatible with shrimp if there are plenty of algae in your tank. In addition, your aquarium should contain live rock, some sea anemones, and aquarium plants. These plants and animals will help keep your water clean and safe from harmful toxins that can harm your fish.

Some of the plants you can use are sea moss, red hair algae, and java fern. While java fern will not help with your water chemistry, it is an easy plant to maintain. It will provide you with a beautiful green accent in your tank that fish and other marine life love!

Anemones like mushroom anemones or bubble tip anemones can also be great additions for pajama cardinalfish tank mates. In addition, having some robust corals will add beauty and diversity to your aquarium environment!

Pajama cardinalfish breeding

pajama cardinalfish

Breeding of Pajama cardinalfish, Sphaeramia nematoptera, is not really very hard, but will only work in certain conditions. The most important thing is that you have a proper tank set up and run by someone who really knows what they are doing. They like living in a brackish water environment between pH 6-8 with lots of live rock and sand substrate.  Add some live soft corals into your tanks such as mushrooms or Leathers.

In an aquarium setting, breeding Pajama cardinalfish is one of the most rewarding experiences. Being such slow-moving fish, they are easy to breed in an aquarium with live rock, healthy water, and lots of hiding spots. They will pair up and lay eggs between rocks.

The female lays batches of eggs every other day until she has laid 30 to 50 eggs total on different days over a period of three weeks. Young Pajama cardinalfish go through several color changes as they develop into adults: first, they become blue-gray; then they take on shades of deep red; finally, they turn silver or white as adults.

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Are Pajama cardinalfish aggressive or peaceful?

The pajama cardinalfish is one of many species that are very peaceful, but they do have some aggressive tendencies. There are instances where they can become territorial and chase other fish away in their tank, but these instances are rare.

Pajama cardinalfish care

pajama cardinalfish

Among some of the most popular marine fish in captivity, pajama cardinalfish are well-equipped to keep themselves healthy, though they need some help from you.

Pajama cardinalfish food

The cardinalfish diet is mainly composed of algae and plankton. In captivity, they will eat almost any high-quality prepared flake or pellet food. Some hobbyists have had luck with sinking dried shrimp pellets and frozen brine shrimp as well. They also like fresh veggies such as cucumber, blanched zucchini, spinach leaves, etc., all of which should be offered in moderation since these foods can cause digestive problems if overfed.

Pajama cardinalfish lifespan

This species can live for up to 5 years in captivity with proper care and good water chemistry.

Parasites and diseases

pajama cardinalfish

When considering whether or not you have parasites, or are affected by the disease in any way, there are two things you should always look out for. First, check if your fish’s body appears bloated or distended. This can be a sign of intestinal worms that are living within your fish’s intestines.

The second sign to watch out for is white spots on your fish’s skin and fins. These could be signs of Ichthyophthirius multifiliis infection, a.k.a. ich. Both worms and ich suck nutrients from your fish’s body which makes it weak, leading to stress-related diseases and even death.


Juvenile pajama cardinalfish are preyed upon by larger marine fish, so keeping them in an aquarium without other tankmates is ideal. If you must keep them with other fish, make sure your pajamas are added to a tank after all of its inhabitants have settled in and gotten comfortable.

Some examples of predators are butterflyfish, bass, triggers, and other larger angelfish. A pajama cardinal will also be out-competed by any other fish that is seeking live meaty foods. You can tell if your cardinal is being eaten or stressed by looking at their body language.

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If they lay flat on their side or swim upside down, it means there may be something bothering them such as poor water quality, low oxygen levels, lack of food, or other tank mates eating them.

Do they make good pets?

Yes, pajama cardinalfish make great pets. They are very easy to care for, being a good choice even for beginners. They are reef safe, so they don’t harm corals or other small inverts.

Pajama cardinal vs. banggai

pajama cardinalfish

The pajama cardinal and banggai cardinal are very similar, with only minor differences. Both types of fish have vibrant coloration, which adds life to their aquascape. These colors can fade slightly over time if your tank is not kept clean enough or if there is not enough sunlight in your home.

You can keep either type of fish together in an aquarium; however, you should keep at least one male and one female. If you put multiple males together in an aquarium, they will fight over territory and other resources.

The pajama cardinalfish has elongated fins that are pale red to white in color with blue highlights, while those of its look-alike, the banggai cardinalfish, are shorter and reddish or orange. The pajama also has a deeper body shape with longer dorsal fin spines, while those of its look-alike have shallower bodies with shorter spines.

The stripes on both fishes’ cheeks and brows are relatively faint compared to their more colorful cousins, like neon tetras. Also, these two species have a different natural habitat; whereas banggai cardinals live in saltwater areas near coral reefs and mangroves (hence their other common name mangrove cardinalfish), pajama cardinals live in saltwater environments such as swamps or flooded forests.