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Killifish Male vs. Female (How to Tell Them Apart)

Killifish Male vs. Female (How to Tell Them Apart)

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This post is written to the author's best knowledge and is not intended to be used in place of veterinary advice. In addition, this post may contain affiliate links. As an Amazon Associate I earn from qualifying purchases.

There’s a good chance that you’ve seen killifish in someone’s fish tank or at an aquarium store. They’re great fish that are incredibly beginner-friendly.

These fish could be an excellent addition to your tank. You might even like them so much that you’ll want to breed them.

Of course, to be able to breed fish, you’re going to need a male and a female fish. At first glance, you might not be able to tell a male apart from a female without a bit of experience.

What are the differences between male killifish and female killifish? Are they hard to tell apart, or is it easy to do once you know what to look for?

Read on to learn everything that you need to know to determine the gender of killifish. This should make it easier to get the fish that you need for your tank.

How to Tell Male and Female Killifish Apart

The first thing you should know is that this information can differ a bit depending on the species of killifish that you’re looking at. Some might have more minor differences, while others will have differences that are more pronounced.

Since there are so many types of killifish, it isn’t practical to go over each species here. Instead, it’s best to focus on general information that can help you to easily differentiate between males and females.

The vast majority of killifish can be identified using this method. Male killifish are typically going to be a bit larger than their female counterparts.

They’re also known for having larger fins. Males have vibrant and showy fins because they use them to attract females for mating.

This is also why male killifish are far more colorful than females. Females will have duller bodies that are slightly rounder.

When looking at the anal fin of the fish, you’ll see that males have a pointed anal fin. Females generally have rounded anal fins.

You can also see eggs in the abdomen of the female if you hold a flashlight up to it. You can do this by bagging the fish carefully and then using the light to try to spot the eggs.

Is Breeding Killifish Easy?

Killifish are very easy to breed. You just need to make sure the conditions are right in the tank.

There are different types of killifish, though. Some lay eggs on floating plants while others lay eggs in the ground.

The fish that lay eggs on floating plants are known as “egg hangers.” You can replicate the floating plants in the fish tank by using a spawning mop.

A male and a female fish will mate, and then the female will lay its eggs on the spawning mop. You can then remove the mop from the tank or put the parent fish in a different tank.

Killifish are known to eat their own eggs, and they will also eat their babies. So it’s best to separate the parents from the eggs.

The eggs should hatch in six weeks so long as the conditions remain optimal. When breeding killifish that lay their eggs in the ground, it’s necessary to provide them with peat moss as the substrate material.

It must be deep enough, and the eggs need to go through a dry period. This is what happens in the wild because these types of killifish live in non-permanent bodies of water that dry up during specific times of the year.

You put the eggs through a dry period, and keep them in the peat moss. Then, after a certain amount of time passes, you add water to help the eggs finish hatching.

It’s a lot easier to breed the egg hangers, but taking care of the eggs in peat moss won’t be too hard, either. So long as you have males and females, it’s easy to breed these fish.

Do Killifish Live for a Long Time?

No, many types of killifish don’t live for very long at all. Some can live for several years, while others will only live for eight months or so.

Above, you learned that there are killifish that live in non-permanent bodies of water. These fish have evolved to go through their life cycle faster than usual.

This is done so they can reproduce faster and lay their eggs before the body of water that they live in dries up. These killifish are known as annual killifish, and they have rather short lifespans.

There are also semi-annual killifish that are similar, but the waters they come from don’t deal with dry periods quite as often. They might live a little longer.

Non-annual killifish can live for years because they come from permanent bodies of water. They don’t have to worry about the water drying up and don’t need to evolve to work around the disappearing bodies of water.

Are Males More Aggressive Than Females?

Male killifish are generally more aggressive than females. You should know that males are known to fight and compete for females, too.

This is why it’s wise to keep one male killifish in the tank with two or three females. Most say that keeping two males in the same tank is a poor idea.

Don’t think that female killifish can’t be aggressive, though. Some species of killifish are rather aggressive, and the females will be aggressive just like the males.

Final Thoughts

Now you know how to tell males and females apart. Killifish can be easy to tell apart once you know what to look for.

Males are generally bigger, more colorful, and have flashier fins. Females are smaller and have rounder bodies than males.

You can also see the females holding eggs if you shine a flashlight near the belly area. As always, be careful when bagging the fish to check such things.

Use this information to ensure that you can buy a male and a female killifish. Remember that it’s best not to keep more than one male killifish in a fish tank.

You want to keep the fish from fighting. One male and two or three females will be ideal.

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