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With small schooling fish like the Neon Tetra, it can be very difficult to determine the sex of them. This is however often necessary if you wish to breed your fish – and neons are one of the most popular Tetra species for beginners to breed that have also been bred in captivity for the longest.

Fortunately, for the trained eye, it’s not too tough to learn the subtle signs that tell Neon Tetra males from females. Thus you can use this guide to determine which is which, so read on.

Neon Tetra Male And Female Differences

Not all schooling fish are the same! Just like there are significant differences between types of Tetras, the Neon Tetra itself is not a monolith and there are indeed some differences between the females and males. It’s easy to think of these fish just as one school, especially if they’re not the main exhibit in your tank. However, they actually have a surprisingly complex life and mating cycle adapted to their home in the river basins of South America.

Are There Significant Differences?

There are significant differences between male and female Neon Tetras in terms of shape because of the female Tetras body capacity for carrying eggs. There are also behavioral differences in aggression and in how fish act towards each other and other tank mates, all of which will be covered later on in this article.

Why Might You Need To Know The Difference?

It’s important to know the difference between male and female Neon Tetras if you wish to breed your fish. After all, it might be challenging to get any eggs if you create a breeding tank that has only females! However, understanding male and female Neon Tetra differences can actually be useful in sorting out fish aggression and preventing common tank issues such as fin nipping. However, for now, let’s take a look at simply telling the sexes apart.

Neon Tetra Male VS Female Appearance

Male and female Neon Tetras are relatively similar on the surface. However, if you want o tell them apart, you can look at the 3 S’s:

1. Size

Size! Simply put, female Neon Tetras are slightly bigger than male Neon Tetras. Generally, they look bulkier in shape, and they have a rounded and chunkier appearance in addition to the actual size difference.

It may not sound like much as technically the difference is only a few millimeters in length and height, however, when you see a group of these fish together, it is quite easy to pick out the larger females.

2. Shape

As mentioned above, female Neon Tetras have a slightly chunkier and bulkier shape in addition to their larger size. However, they also have a more rounded stomach, even when they are not pregnant. This is because the female Neon Tetra needs extra space in her abdomen for the uterus, where she carries her eggs.

Of course, the difference becomes very noticeable when you have a pregnant female Neon Tetra. These fish are unmistakable due to the rounded shape of the eggs in their distended stomachs.

3. Stripe

All Neon Tetras have an attractive blue neon stripe that gives them their name. However, on the male Neon Tetra, partly due to their more streamlined body shape, this stripe is straight and runs directly along their body. However, on the females, the stripe is curved gently and follows the curvature of your fish’s back and abdomen. It’s a subtle difference but it’s a great way of telling the sexes apart once you know what you’re looking for.

Neon Tetra Female VS Male Behavior

You may assume that the only time you need to know the difference between the sexes of these fish is when they are breeding. However, there are certainly some differences in behavior that manifest outside of the mating period as well. Read on to understand some of the main ones both surrounding breeding and outside of it.

1. General Behavior

• Competition Over Mates:

Many studies have shown that male fish in many species, including the Neon Tetra, can become competitive and territorial towards other males when in the presence of a female. Fish like Neon Tetras, which are fin nippers, may direct their attention towards other males that they see as a threat or challenge.

Generally, female Neon Tetras will not display aggression in these circumstances, although they may show aggression when they feel threatened by stress, overcrowding, or poor water conditions. This is important to spot as if left unchecked these conditions can lead to Neon Tetra death from factors other than aggression. However, how is it possible to tell the difference between types of aggressive behavior?

Generally, you can use a process of elimination. In fact, you can see if there are any factors that may make your fish stressed and prone to fin nipping. These generally include small tank conditions and poor water quality. However, if you have ruled these out and there are still fish that are chasing and nipping each other, it may be that these are males acting aggressively in the presence of the female.

As ultimately it is the female fish who has the say in which males get to mate with her, competition between males can be high. To minimize this, you can increase the sex ratio so there are more females, or you can add more fish. Neon Tetras are generally calm fish and as with all schooling fish, aggression is most prevalent in small groups of 3 or 4 fish as opposed to a larger school of 5-7.

2. Behavior During Mating

Of course one of the most obvious areas where male and female Neon Tetra behavior is different is during the mating and courtship ritual.

What triggers mating? Generally, in the wild, spawning and mating are triggered by light, especially sunlight. Keeping your breeding tank in a sunlit space can be a good way of simulating these natural conditions.

However, neon Tetras can be sensitive to light in general. Thus, it is best to use natural light instead of a strong artificial LED light.

Once the mating ritual begins, you will see the male Neon Tetra chase the female in a square shape. This will happen until she drops her eggs, which the male will then fertilize by spraying his milt over them.

Author’s Note: Sometimes, not all eggs get fertilized. In fact, occasionally as little as a third of the eggs get fertilized! This is why Neon Tetra females lay so many eggs – up to 160 in some cases. When you add to this the fact that in the wild some eggs may not hatch, may get eaten by predators, or even that some fry may get eaten by predators too, it makes sense that the female lays so many eggs.

• Neon Tetra Fry Growth And Lifecycle

Neon Tetra fry start off very difficult to tell apart in terms of the sexes. Generally, they look like small, translucent aquatic microorganisms. You may not even recognize them as fish at first!

Differentiating between the sexes is only possible when fish grow to maturity. The Neon Tetra is mature after about one year of age, but the difference between the sexes generally shows up much earlier than this, at about 4-6 months.

After about two months, you will be able to see your fish like small adults. After about three months, they will be large enough for you to move them back into your main tank.

Male vs. Female Neon Tetra Size, Care, And Suitability

After reading about these important sex differences you may wonder whether there is any difference in suitability for beginner aquarists. Thankfully, these fish are nothing like the betta or some species of Gourami where keeping a female sorority tank is very different from keeping a lone male. Generally, you can simply keep a school together.

Ideal Sex Ratio For Neon Tetras

In some major mainstream aquatics stores, you may simply be sold a school of Neon Tetras to keep together. This can happen especially if you are a beginner who is not clued up on the ins and outs of Neon Tetra care and why sex ratio can be important with fish.

You may hear people talk about the sex ratio for guppies and mollies, especially in the context of female fish getting harassed by males.

This sort of harassment is not such a big issue with Neon Tetras. They are social and peaceful and because they are not livebearers – therefore the male does not actually have to impregnate the female – you don’t get too many issues with chasing and male-on-female aggression. However because male-male competition does still happen, keeping a sex ratio of two females to every one male can be useful to ensure harmony in your tank.

Author’s Note: It’s a good idea to keep a larger rather than smaller number of Neon Tetras. These are social fish that need group information to thrive. If you keep them in a group of under three, or even three to four, they will become stressed and start acting aggressively towards each other or other tankmates. This is because in the wild, they need safety in numbers as protection from predators. Thus, they feel safest in a larger rather than smaller group. You can even keep a group of up to ten or twenty together if you have the right size tank!

Bottom Line

The differences between male and female Neon Tetras are subtle but significant and as a result, it’s important to sex them correctly if you want to fully understand their lifecycle, behavior, and their proper needs. As with any fish, you can simply meet their basic requirements.

However, to really see them thrive, knowing the ins and outs of their breeding and behavior will allow you to take your fishkeeping further and maintain a successful community tank with multiple generations of fish.

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