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!

PJ Cardinalfish Overview

Here is a brief overview on the pajama cardinalfish, in both graphical and in text form:

  • 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, making them one of the hardiest saltwater fish 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 a maximum of 3.1 inches in length (8 cm).
  • 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.
  • Their salinity range must be between 1.020 and 1.025.
  • The pH levels should be between 8.1 to 8.4.
  • The temperature in the tank has to be between 72°F to 78°F (22°C to 25°C) 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, corals, live rock and other holes is essential for these fish.

Pajama Cardinalfish General Information

Other names the Pajama Cardinalfish goes by are; Spotted Cardinal, Spotted Cardinalfish, PJ Cardinalfish, Pajama Cardinal & Pajama Cardinal fish.

Typically, when in the wild, they surround themselves with small shoals of their own kind, and reside in the western Pacific Ocean, occupying the waters from Java to Fiji.

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!

Equally, they are peaceful fish that get along well with a whole host of different fish, which in return, creates a very harmonious reef community environment.

Pajama Cardinalfish Appearance

Their body is 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 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!

Pajama Cardinalfish Behavior

Due to their 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 For?

Their lifespan is typically between 2 and 5 years, provided you look after them correctly and feed them a balanced diet.

Differences Between Male and Female Differences

Desiphering the genders of both male and female pajama cardinalfish is actually easier than it is for their cousins, the banggai cardinalfish. This is due to the males having a longer secondary dorsal fin than females.

Females will also have slightly rounder and larger bodies than males. Also, something interesting to note is that when they breed, they are mouth brooders.

This means that the males will carry the fertilized eggs in their mouths for almost an entire month before they hatch!

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 pairs, and even large groups! 

They are certainly considered to be reef safe and will not harm or bother any other members of your community, including invertebrates.

Tank Size - How Many Pajama Cardinals Should I Get?

Despite being small fish, we believe that they should live in a minimum tank size of 30 gallons (114 liters). This is a good size for keeping just one or two pj cardinals.

Below is a graphical summary of a classic 30 gallon tank, including the filled weight and empty weight:

They are slow but methodical swimmers so you want to give them enough room and you should also house them with equally peaceful tank mates.

The awesome thing about the Pajama Cardinalfish is that they can live in larger groups too.

So, if you wanted to keep more than one or a pair, then you should probably keep them in a 55 gallon (208 liters) tank as a minimum.

Below are the dimensions for a classic 55 gallon saltwater aquarium:


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, being micro predators, so, it would help replicate their natural environment to feed them live foods at those times on occasion.

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. Also, 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 72°F to 78°F 22°C to 25°C.

The graphic below summarizes their water parameters, from ideal temperature, to gravity ranges, and ideal pH levels:

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.

Unique patterns and simply incredible coloration will be on full display in a large aquarium with varying shoals of fish for them to join. 

Here are some brilliant choices for pajama cardinalfish tank mates:

  • Clownfish
  • Gobies
  • Dwarf angelfish
  • Reef safe wrasses
  • Pufferfish
  • Chromis fish

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.

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.

Final Thoughts on Pajama Cardinalfish

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!

We hope that you have found this care guide a useful resource - feel free to download any of our useful graphics and images with summaries and overviews!