Pajama Cardinalfish – Learn Everything About The Sphaeramia Nematoptera

The Pajama Cardinal truly is a special fish, originating from the Coral Sea in the Indo-Pacific, and only found in areas surrounding Northern Australia, Papua New Guinea, the Philippines, and Indonesia. The scientific name for this incredibly unique fish is the Sphaeramia Nematoptera. They make for an awesome addition to almost any saltwater aquarium environment. So, let's dive in and learn everything we can about this fascinating fish!

Pajama cardinalfish

PJ Cardinalfish Overview

Here is a brief overview on the pajama cardinalfish. More detailed information can be found throughout the article:

  • Despite being somewhat small in size, they will require a tank size of 30 Gallons or more (114 Liters), mostly because of how active they are, requiring more space for exploration and swimming.
  • They are not prone to disease, which is always a relief, especially for novice hobbyists. There is nothing worse than having a diseased fish when you are only just starting out.
  • They are incredibly good fish for beginners, and experts alike and will make for a fantastic addition to your community.
  • The adults will grow to 3.1 inches in length (8 cm) and are a perfect 40 gallon aquarium fish.
  • A make or break when it comes to many saltwater tropical fish is, “are they reef compatible?”, the answer is yes, which is great for everyone involved, most of all your aquarium!
  • Another question that is posed a lot is whether or not a fish can hang with the big guns, and by that, we mean if they can live with predator fish in harmony without being injured or killed - unfortunately, these fish cannot live with predators, and you are strongly advised to keep them away from any predator fish.
  • The Pajama Cardinalfish are incredibly easy to care for and look after, with minimal dietary requirements and a good attitude.
  • The pH levels should be between 8.1 to 8.4.
  • The temperature in the tank has to be between 24°C to 28°C (75.2°F to 82.4°F) for them to survive and thrive.
  • They will usually hang around the middle level of your tank, which is honestly our favorite level, especially when you have a fish that you want to look at as much as this beauty.
  • Having many hiding places like caves, plants, and other holes is essential for these critters.


The fish itself sports an incredibly unusual array of colors and patterns, almost resembling that of the Bolivian Ram, however, these are totally different fish!

Their body is somewhat divided into colors, with the face and first half of the body being a bright yellow, then a rather thick and vivid black line running along the middle and leaking onto the two fins. Another perhaps unique characteristic of these beautiful fish is their eyes, they are larger than most fish and that is because they are nocturnal.

This doesn’t mean they spend all day hiding or sleeping and only come out at night. They tend to be out both in the day and night – they are terribly busy fish! The rest of the body and tail is comprised of a pearl-white color with many black/brown spots, almost resembling a Zebra. The Pajama Cardinalfish is truly remarkable and striking!


Due to their incredibly peaceful nature and social behavior, they are the perfect saltwater fish for new hobbyists looking to start building up a strong community for their aquarium. They are well-behaved and will not cause any trouble in your aquarium, which is brilliant news for any saltwater hobbyist.

How long do pajama cardinals live? Their lifespan is typically between 2 and 5 years, provided you look after them correctly and feed them a balanced diet. Other names the Pajama Cardinalfish goes by are; Spotted Cardinal, Spotted Cardinalfish, PJ Cardinalfish, Pajama Cardinal & Pajama Cardinal fish. Usually, when in the wild, they surround themselves with small shoals.

Male and Female Differences

Identifying the gender of any fish can be hard work, it isn’t as easy as finding out if a dog is a boy or a girl. However, these fish are even harder than most, as they grow older, it may become a bit easier to identify as the males should become slightly larger and the females will usually begin to swell due to carrying eggs. One of the best ways to decipher a male is when they start mouthbrooding the fry.

Pajama Cardinalfish

Tank Requirements and Setup

Not only are these fish awesome in their personalities and peaceful nature, but they aren’t too fussy either. A small or large tank will do for them, and they are also happy to be kept singularly, in small schools, and even large shoals! They are certainly considered to be reef safe and will not harm or bother any other members of your community, including invertebrates.

Tank Size

Smaller tanks for the Pajama Cardinalfish should still be a minimum of 30 gallons. They are slow but methodical swimmers so you want to give them enough room and you should also house them with peaceful tankmates.

The awesome thing about the Pajama Cardinalfish is that they do not necessarily need to be in schools or shoals to live a happy life. Being with a partner or living solitary are options that can be explored in addition.


They are carnivores, and also extremely fast eaters, it is important to make sure you are feeding the entire tank rather than just the Pajamas because they can be greedy. The best foods to feed them would be high-protein meaty foods such as mysis and brine shrimp as well as pellets and flaked food to add a bit of variety. They also prefer to hunt and eat at night time, so, it would help replicate their natural environment to feed them at those times, although it is not essential.

Acclimatization and Water Quality

The acclimatization for fish can vary from species to species, and for the Pajama Cardinal it is no different. Firstly, you will need to place your fish in a bucket and then drip acclimate for around 45 minutes at a rate of 3 drips per second, which will bring the fish’s water parameters the same as your tank.

Once the fish has been drip acclimated you will need to catch it with a net and place it gently into your tank. Avoid putting any of the water the fish originally travelled in, into your tank. Once this is done, your Pajama Cardinal is acclimated and ready to live a healthy and happy life in your aquarium. Pajama cardinalfish also require a water temperature between 24°C to 28°C (75.2°F to 82.4°F).

Pajama Cardinalfish Tank Mates

The great thing about these fish is that they are super independent but also confident and make for brilliant tank mates. They will suit almost any community they swim into and do not mind how big or small the community is. Their unique and simply incredible coloration will be on full display in a large aquarium with varying shoals of fish for them to join. They are so easy to manage for any level that you really don’t have much to worry about at all with them.

Can pajama cardinalfish live alone? Sure, they certainly can live alone provided all their other requirements have been met. However, due to their social nature and interesting behavior when interacting with other fish, you will ideally want to house them in pairs.

Pajama Cardinalfish

In addition to this, if you own a shy fish that enjoys hiding away for hours on end that you really want to see have a growth in confidence, the Pajama Cardinal Fish might just be the perfect tank mate for them. They have been known to bring other fish out of their shell, literally, due to their sheer confidence and likeability among other fish.

Unfortunately, keeping them in a tank with predators will spell a short life for these fish, they simply do not grow big enough to not be preyed upon. It is highly likely they could become dinner for bigger and more aggressive predator fish, such as Groupers, Triggerfish, and of course, Lionfish.


In conclusion, these fish are truly brilliant, not only are they beautiful on the outside, but they are beautiful on the inside too. They are great for any level hobbyist and bring in character and aesthetics to any community they join, big or small!