Mandarin Fish, along with 19 other genera, make up the Callionymidae; a family of fish that contains almost 190 species. All of these fish are marine fish and many of them are distributed across the Indo-west Pacific.

While some of these fish live on reefs with sandy patches, such as the mandarin fish that we’ll look at in this article, many spend their lives on sandy bottoms and survive by eating small, bottom-dwelling invertebrates.

A Beautiful Mandarin Fish

A Beautiful Mandarin Fish –  Photo Credit – Lviatour

The Longtail Dragonet (Callionymus gardineri) is the largest member of the family and it grows up to 12 inches long. The Saint Helens Dragonet (C. Sanctaehelenae) is the smallest fish in the family and only ever reaches about 0.8 inches long. The species that we’ll be looking at in this article are the S. splendidus and the S. Picturatus each reach around 4 inches.

The slope dragonets are a little related to this family but are considered to be members of the Draconettidae family. This family is much smaller than the Callionymidae family and only has around 14 species spread across the two genera of Centrodraco and Draconetta. The slope dragonet fish look more like the streamlined dragonet relatives of Synchiropus. They are mostly found on sea mounts and along the edge of the continental shelf.

As such they are never found in the hobby. In terms of their general appearance mandarin fish also closely resemble the combtooth blennies fish of the Blenidae family or the gobies from the Gobiidae family. They are set apart as being their own family by their fin and skeletal features.

Protective Poison

Due to the stature, color, and speed of these bottom dwellers one might feel that mandarin fish were an excellent target for predators. This assumption would be wrong however as their vulnerability is designed to hide their toxic defense mechanisms.

Mandarins are much like any other fish that doesn’t have scales in that they release a body slime that they use to protect themselves and swim through their habitat safely. It’s also believed that this body slime gives them the ability to swim swifter through water but no one is quite sure how much it improves their swimming speed.

One important thing about this slime is that it can protect them from parasites and also helps mandarin fish stay free of disease. Perhaps the most important thing about it though is that predators find the taste and smell of the slime distasteful. This makes them decide that mandarin fish aren’t worth eating when they are hunting for food. There is also a good chance that the bright colors of the S. Splendidus are there to warn other predators to stay away. This is a common defense mechanism seen in nature.

As well as the foul smell and taste mandarin fish also have sacciform (saclike) cells on their skin. These cells create a toxin that also protects them from predators. While they serve a similar function to the slime producing cells the sacciform are considered separate.

The good news for aquarists is that mandarins do not typically release their toxin during normal circumstances so your mandarin fish is unlikely to attempt to poison you or your other fish. If they were too trigger happy with their toxic secretions then it would be a bad idea to keep them in a mixed aquarium as it would potentially harm or even kill their tankmates.

The only time the mandarin fish is likely to release its poison is when it is placed under extreme stress. This kind of stress is something that could only really be generated by a predator or when scooping up the fish and moving it between tanks. Even if you move it between tanks it is not likely to release its toxin. If you want to be safe then you should use the net to gently guide the fish into a transparent container without actually trapping it with the mesh. You can then lift the container and move the fish into its new home without it even realising that it’s been trapped and stressing it out.

Mandarin Fish Selection

There are only two different species of Synchiropus that are kept in home aquariums on a regular basis. We’ve included information on five because we expect that we’ll hear more about the other three in time. One of these species does occasionally turn up in stores. These fish are typically collected as a bycatch.

Synchiropus Splendidus

Synchiropus Splendidus

Synchiropus Splendidus

This fish breed is commonly known as the mandarin fish, blue, green or striped mandarin fish, the psychedelic fish, the picturesque dragonet and also the mandarin goby (but remember that this fish is not a goby fish). They are usually found in the Western Pacfici between the Ryuku Islands and Australia. The maximum total length of this fish is around 24 inches but if you keep them in optimal conditions in an aquarium they can sometimes grow bigger.

Notes: This brightly colored species is commonly thought of as being the most beautiful aquarium fish there is. Also note that males are intolerant of each other and will fight; sometime to the death. You must keep them with non-aggressive tankmates. There are captive-bred stocks of this fish in some stores.

Synchiropus Picturatus

Synchiropus Splendidus

Synchiropus Splendidus –  Photo Credit – Bajoelmar

This fish is commonly known as Spotted mandarin fish, spotted green and psychedelic mandarin fish; psychedelic fish; picture dragonet; green-spot mandarin goby (again this is not a goby fish) and the target-spotted dragonet.

The range for this fish is the Indo-west Pacific and it can be found from the Philippines to Eastern Indonesia and Northwest Australia. The total length of this fish is around 24 inches but they can grow larger in the right aquarium.

Notes: This fish, along with the S. Splendidus, is one of only two fish that are reported to show blue coloration. The difference is that this fish has fewer blue areas than the S. Spledidus.

The body base color of this fish is green and it’s important that any tankmates you get for them are non-aggressive. Much like the Mandarin Fish you can buy captive-bred stocks in some stores. While there are other blue invertebrates mandarins will generally get their color from blue cellular pigment rather than through the thin-film interference from piles of flat, thin and reflecting crystals that are responsible for other blue invertebrates. This pigment is produced within specialised intra-cellular structures (organelles) that are commonly called cyanophores. While it is possible to breed these fish in home aquariums it isn’t that common.


There are still reports of successful breeding on the internet. Some people have even uploaded egg and sperm release videos. It could very well be a matter of time before this rare occurrence becomes more commonplace. It is possible that females will begin to produce eggs and males will become more active as long as the fish are well-fed and are relaxed. If it all goes well then a pair of male and female fish will line up alongside each other, swim together away from the substrate, release their eggs and sperm, and then go back to the bottom of the tank. After every egg has been released (and there are typically 200) the breeding pair go back to what they would normally do and the eggs will float unattended. This spawning will often take place weekly, if not more frequently, over the course of a few months.

It won’t take very long for the eggs to hatch as it typically takes around 15 days. It will take another four days for the fry to begin feeding on even the smallest pieces of food such as the rotifers or “green” water, which is water loaded with phytoplankton. It is difficult to raise mandarins through this phase but it isn’t impossible. The main challenge is to get them to feed, which is made more difficult given their small size; a problem found with most marine life as well as mandarins. We haven’t dedicated a lot of space, if you’ll pardon the pun, to space requirements.

We recommend looking through internet and books, as well as talking with other mandarin fans, to learn more about breeding and rearing mandarin fish. If you are able to successfully rear and maintain your mandarins then you’ll be entertained by them for years. There was a time when you could only expect your mandarin to survive for between 2-4 years in an aquarium but advancements in technology, along with husbandry methods, foods, and knowledge mean that we’re closer than ever to giving domesticated mandarins the same 10-15 years natural lifespan their wild counterparts enjoy.

The Mandarin fish has to be one of the nicest looking fish with one of the most fascinating temperaments that you can keep as a hobbyist. Get down to your local fish store!

Feeding Your Mandarin Fish

As well as setting up a refugium and giving your mandarin fish plenty of access to pods you also need to offer them different foods.

One problem with mandarins is that they can be very fussy and challenging to feed if you don’t give them a natural supply of food. The good news is that you can get your mandarin fish to accept gut-loaded brine shrimp with a little bit of patience and perseverance. Gut-loaded brine shrimp have plenty of rotifers in their gut and provide your fish with far more nutrition than a basic brine shrimp can.

Eventually the mandarins will have a feeding response to the live brine fish. It could take a little while at first but after they become acclimated to feeding on live brine shrimp you can mix in some thawed-out frozen mysids, along with other small invertebrates in with the brine shrimp. Eventually the brine shrimp will begin to pick at and eat these other invertebrates and you might even reach the point you can stop feeding them live food and can just give them the thawed-out invertebrates instead.

Remember that mandarins are slow moving bottom feeding fish. As such you should always turn off the filtration and aeration equipment for a few minutes while your fish eat so that they have the chance to hunt down their food.

There are some enterprising aquarists out there who have managed to train their mandarins to eat “dead” food and even granulated food. It can take some perseverance and ingenuity but the main factor is to put the food within a clear glass container, such as a bottle. Make sure that the neck of the bottle is wide enough for mandarins to have access to it without it being large enough for their more aggressive tankmates; such as tangs.

There are a lot of positives to this method that make it worth recommending. For a start it ensures that slower mandarins have access to food because they won’t have it stolen from them and they won’t need to compete with their tankmates for food during feeding time.

Feeding Synchiropus fish is becoming easier with the introduction of commercially bred and raised Synchiropus fish. They are all reared on commercial foods and so you should have no trouble getting to eat these commercial foods after they settle into their new aquarium.