Neon Blue Rasbora – The Perfect Blue Nano Species

This is a picture of our Neon Blue Rasbora (Sundadanio axelrodi 'blue') in our Mr. Aqua 12 Long Aquarium

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Looking for a species of fish that grow to be less than an inch at full maturity? Want a blue colored fish besides Neon or Cardinal Tetras? Continue reading to learn about the Neon Blue Rasbora (Sundadanio axelrodi ‘blue’), a little gem of a fish that I stumbled upon one day while perusing one of our favorite local fish stores.

Why is such a small species important to us?

If you have read the article I wrote about our setups, you would know that the largest aquarium we keep is 12 gallons. We have a small home and love to aquascape, and like most enthusiasts that are passionate about this hobby, have several setups. Having a small house is not the only reason we keep smaller tanks, but the desire to scale nature to a specific size is part of the attraction for us. Having a species of fish that grows to a maximum size of 1 – 1 1/4″ is important to keep the scale of our layouts balanced.

Neon Blue Rasbora habitat requirements

According to Seriously Fish, the Neon Blue Rasbora (Sundadanio axelrodi ‘blue’) comes from blackwater pools and streams that are associated with ancient forest peat swamps. It is recommended that they be kept in a blackwater type aquascape with leaf litter and tannins to soften the water to a pH of no more than 5. Temperature requirements for the Neon Blue Rasbora are 73 – 79 degrees, and lighting should be kept to a minimum to replicate their natural habitat. In researching the type of environment this species originates, it is safe to conclude that it would look and act its most natural in a biotope type display.

Sexing and behavior

During my research, I found that males have a dark anal fin, almost black. After reading that, I was able to count 2 males to 6 females in our aquarium. The demeanor of the male Neon Blue Rasbora seems to be dominate and territorial. Not only do they exhibit chasing behavior to their species, but other species as well.

Neon Blue Rasbora Recommended diet

There is limited information on these guys compared to other species of livestock. According to online retailers, they are omnivores and like flake food as well as freeze dried Tubifex and Bloodworms. Other research suggests feeding them Cyclops, Daphnia, and chopped Bloodworm. They are picky eaters, and unlike some fish that will eat frozen Bloodworms three times the size of their bodies, they only eat what they can fit in their mouth.

What we feed them

We discovered that they will take Cyclops, finely chopped frozen bloodworm, and high quality Bloodworm flakes. On several occasions I offered them Daphnia, but they didn’t seem to care for it. Periodically they will eat Seachem Chorella Flakes which consist of Chlorella algae. I have read this is known as a superfood for our livestock, but have not researched this yet. In my experience feeding this type of food to our livestock, I noticed the animals will emanate brighter colors. You can find out more about Chlorella flakes on Seachem’s website.

It was couple of days before they took any food from us. This was cause for concern at first. I truly thought I found a species of fish that I would not be able to care for. Most of our fish will eat until they burst, but the Neon Blue Rasbora is different. They give the impression that they are light eaters, meaning they seem to take just a few pieces of food and then stop eating. They continue to nibble, but taste food and spit it out. I often wonder if they like what we are offering them. We have had them for over a month and they are growing and healthy. I believe that is a sign that we are meeting their nutritional needs.

This is another picture of our Neon Blue Rasbora (Sundadanio axelrodi 'blue') in our Mr. Aqua 12 Long Aquarium

Our observations in their new environment

When I purchased these fish, their new home was our Mr. Aqua 12 long. I don’t quarantine or drip acclimate fish like some do because I feel the longer they are going through the transition process, the longer they are stressed. We trust the LFS that we purchase our livestock from, and know they quarantine their fish before adding them to their display tanks. I floated the bag for about 15 minutes to acclimate the temperature, and then released the Neon Blue Rasboras into the tank. Their only tank mates were about 15 Chili Rasboras (Boraras brigittae), 2 Scarlet Badis (Dario dario), and a bunch of RCS (Neocaridina sp.).

They acted like any other new fish that have been released into a new aquarium. They swam to the middle of the tank where we have a large piece of driftwood and huddled there for about an hour before they realized that no one was going to eat them. When they finally came out, they stayed grouped in that area of the tank. The funny thing is, they seemed to claim that area the whole time they lived in that setup.

This is another picture of our Neon Blue Rasbora (Sundadanio axelrodi 'blue') in our Mr. Aqua 12 Long AquariumOur 12 long is just that – long. Our Chili’s like to swim the whole length of the tank, and it’s fun to watch them shoal and swim back and forth. The Neon Blue Rasbora acted different, they never left their territory in the middle of the aquarium.

My observation is that they are pretty peaceful, but a little too boisterous for the smaller Chili’s. In a tank that small, they seemed to dominate and disrupt the harmony that we had in having a Chili Red Rasbora only tank.

This is a picture of our Neon Blue Rasboras in their new home in our Mr. Aqua 8 gallon rimless

We found them a new home

Due to their dominance, we moved them in with our Phoenix Rasboras that live in our 8 gallon rimless. They are now similar in size to the Phoenix Rasboras, and seem to get along fine with them. Nobody pushes anybody around.


These are gorgeous little fish, and a must have for any collector. It is my opinion if you are keeping nano tanks, the Neon Blue Rasbora should be kept by themselves or with other fish that are the same size and have the same personality. The other option is to keep a larger school in a bigger tank. I think that Celestial Danios and various other species would be compatible if the setup was large enough and heavily planted. We are eventually going to move them to the 10 gallon in our office, which is completely low-tech. We are going to add a bunch of Almond leaves, Alder cones, Spider wood, and sticks. Almost like a biotope environment, but not quite scientifically correct.

The Neon Blue Rasbora is still kind of a mystery to us and I am still trying to form a relationship with them. If anyone reading this has any suggestions for us on the care of this particular species, we would love to hear from you.

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2 Responses

  1. Mine eat dried brine shrimp and hakari micro pellets easily. I lost 3 in 6 months but I think it was due to parasites. They school with my micro Rasbora and don’t seem to harass them. They are the same size though. I have a 5 gallon nano heavy planted with neocardia shrimp and a few assassin snails and a single Otto.

    1. Hi Elizabeth,
      Thanks for the comment and the info. Dried Brine Shrimp… Interesting. I have never fed any of my animals that type of food, but will definitely be on the lookout for it.
      Out of the eight fish that we originally purchased, we have 5 left. They started out in our 12 long, but as I stated in the article, have since been moved to our 8 gallon with 4 Phoenix Rasboras and 4 Corydoras Pygmaeus. It is heavily planted now (quite overgrown), and they seem to be happy.
      We have discovered that they really like frozen Cyclops, chopped up frozen Bloodworm, and Bloodworm flake. We occasionally feed them Earthworm flake, but only every once in a while, due to it containing a high fat content.

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