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Breeding Dwarf Neon Rainbowfish

About Melanotaenia Praecox

Known commonly as the Neon Dwarf or Praecox Rainbowfish, Melanotaenia Praecox are a small, colorful rainbow fish from New Guinea. They are an interesting schooling species that is best kept in larger groups of 8-10+, with at least a 1:1 ratio of females to males. An excellent community fish, they do well in peaceful setups that are heavily planted.

I keep 20 dwarf neon rainbows - 10 males and 10 females - in my 90 gallon rainbowfish community tank. The neons share this aquarium with other larger rainbowfish species and they get along with everyone. Praecox are active swimmers and will go after most foods pretty aggressively once they're settled into the aquarium, which makes them fun to watch.

Sex can be easily determined based on size, body shape, and fin color when the fish reach adulthood. Both males and females will have shiny, iridescent blueish bodies. Adult male Praecox have red fins, while females have orange/yellow colored fins. Males will also have a larger, taller body shape with a more pointed head while healthy adult females will be smaller than the males.

Male and Female Dwarf Neon Rainbowfish
Male and Female Dwarf Neon Rainbowfish

Setting up a Breeding Tank

Breeding Aquarium
Breeding Aquarium

A breeding aquarium for Melanotaenia Praecox should be kept 73-82°F (23-28°C), and at a PH slightly above 7.0.  As in most cases, aiming for stable parameters is better than aiming for perfection. A tank with a sponge filter is ideal for this because the fry of this species are incredibly tiny at birth.

Dwarf neons are egg scatterrers, so the ideal setup is a bare bottom aquarium with a large portion of java moss or a spawning mop.  I have used both as egg laying substrates and the fish readily spawned in both the moss and the mop.

The purpose of the spawning mop is to give the eggs a safe place to stick to that can be removed and transferred to a rearing tank if desired. You can make your own spawning mop using wool string, or buy them pretty inexpensively.

Selecting and Preparing Breeding Stock

Before moving fish into a breeding tank you'll want to make sure you have a few healthy, well fed adult specimens ready to breed.  As with any fish, a high quality diet consisting of a good variety of live, frozen, and dried foods is ideal to get them ready to breed.  Females need to eat well to produce lots of eggs, and males will display their best colors and breeding activity when well fed.

Look for males with a nice tall body and colorful fins.  Females should be grown out and well fed before being selected for breeding.  I have had good success just selecting one pair and placing them in a breeding aquarium together. 

The pair may take a couple of days to settle into the tank before they start to show breeding behavior.  The male will display for the female and the two will swim through their chosen spawning site, which should be a spawning mop or moss portion.  Eggs will be deposited over the course of a few days, so dont pull the pair out as soon as you see eggs.

Praecox Eggs
Praecox Eggs

Praecox eggs are very small so they can be challenging to spot. Once the pair has spawned, they can be removed from the breeding tank and the eggs will hatch within a week. You can also carefully move the spawning mop or moss with the eggs on it into a fry growout tank with a sponge filter.

Caring for M. Praecox Fry

When dwarf neons hatch they are tiny.  Like, crazy small - less than half a centimeter.  Because they are so small these fry need very fine powdered fry foods, cultured infusoria, or live microworms to feed on.  I would recommend having a combination of very small foods ready before your fry hatch.  Even newly hatched baby brine shrimp will be too large for newborn M. praecox to swallow.

After a week or two on starter fry foods the young should be large enough to take baby brine shrimp, which you should know how to hatch yourself if you want to breed fish.  Baby fish should be fed multiple times a day for optimal survival.  They have very short digestive systems and no accumulated body mass to live on, so they need to eat frequently.

Young M. praecox

M. praecox fry should eat readily and will put on some decent size in just a few months if well fed.  These fish are amazing to watch in large schools, so successful breeding is very rewarding.

6 thoughts on “Breeding Dwarf Neon Rainbowfish

  1. Rebecca

    Hi, how long before you can sex the praecox fry? We have various fry that are about 2-3 months along now, with the largest at about 2cm. However, it doesn’t appear that there are any differences that would indicate male or female ratio.

    1. Crowlin

      Their tails and fins should begin showing color differences at around 3 months if they are being fed several times a day. Make sure they're getting live foods like microworms and baby brine shrimp frequently for optimal growth. They'll start to color up

  2. Christina

    How can you tell if they are full of eggs? I have a very chubby looking dwarf rainbow female in a tank with 2 other females and one male.

    1. Crowlin

      If she's well fed in a tank with a male she probably is ready to spawn. Rainbowfish don't really "fill up" with eggs, they spawn every morning for several days. The eggs are very small and will usually be eaten by other fish unless you have a spawning tank set up.

  3. Aaron

    I have a male and three females.
    A few questions…

    1. Can they all be in the breeding tank? Or is it best for just one male and one female to be in there?

    2. How long should adults be in the tank before I remove them? I saw that they spawn ever day? So I’m a few days I should remove the adult’s?

    1. Crowlin

      I would probably do one male with two females. I let them spawn in the tank for about 10-12 days usually. They lay eggs every morning but you might only get a few eggs per day that don't get eaten if you aren't using spawning mops and pulling them daily. At 10 days the eggs laid on the first couple days should start to hatch out assuming they started spawning immediately, so that's a good time to pull the adults.


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