Raising Healthy Fry: Everything You Need To Know

So you are stuck with a bunch of fry in your aquarium and you aren’t exactly sure what to do with them?

Or maybe you are getting into breeding and want to know all of the ins-and-outs of raising healthy fry?

Whatever the case may be, successfully raising healthy fry is not always an easy task. There’s more to it than simply leaving them be and hoping for the best. 

The water conditions must be almost perfect, you need to feed them the right foods and you must know how to protect them from other fish in your aquarium. 

I’ve written this article to breakdown everything you need to know from the very beginning including: 

• The different types of fish fry and how to identify them
• How to setup the perfect environment for your fry to thrive 
• What you should be feeding your fry
• What to do with unwanted fry

And much more. 

Let’s start by breaking down the many ways in which fish can spawn. It’s important to know what kind of fish fry you are dealing with, so you can adjust your care accordingly. 

Don’t worry, I will try to make it as fun as possible…

There are several different ways in which fish can spawn their young. Knowing which type of spawn you are dealing with can help you tailor your care to their specific requirements. 

Let’s take a look at each type, with some examples of fish that spawn that way:

Bubble Nest

Also known as foam nests, a bubble nest is exactly what it says on the tin – It’s a collection of bubbles, (mixed with an oral secretion – a fancy term for saliva)  that float on the surface of the water. 

The bubble nests are created to protect and incubate the eggs until they hatch. The fish will more than likely be on guard the entire time, to keep the nest safe from other fish. (Usually the male)

Fish that create bubble nests are known as aphrophils and include fish such as:

• Betta Fish
• Gouramis
• Eels

It’s always a good idea to have some floating plants, or at least some corners of your aquarium that are guarded by plants to facilitate your fish’s efforts to protect the eggs.

Mouth Brooders

Mouth Brooding fish are fish that incubate and protect their fry (and even fertilise their eggs) while holding them in their mouth. 

The female will typically hatch her eggs, then collect them in her mouth (the technical term: Buccal Cavity) where the male will spray sperm directly onto the eggs to fertilize them. 

Examples of mouth brooding fish include:

• Malawi Cichlid
• Tanganyika Cichlid
• Arowana
• Cardinal Fish 
• Snakehead

Livebearers

The most common fish found in home aquariums tend to be livebearers. 

Livebearers are fish that carry their eggs inside them, and give birth to live, free-swimming fry. 

Livebearers are often chosen by breeders because caring for live fry is easier than caring for eggs and larvae. 

Their size advantage and ability to swim freely increases their chance of surviving (although being eaten by bigger fish will always remain a threat unless you keep them seperate – more on that later) 

Common examples of Livebearer fish include:

• Guppies
• Mollies
• Platies
• Swordfish

Egg Buriers, Depositors and Scatterers

In almost all cases, if a fish is neither a livebearer or a mouth brooder, they will have some way of releasing their eggs into your aquarium.

Some will scatter their eggs across the entire aquarium or pond (Koi carp for example), some will gently deposit their eggs onto a plant or rock (Angelfish and Rasboras), and others will bury their eggs in the substrate (Killifish).

The way in which your fish deal with releasing their eggs will be obvious to you if you observe their behavior. 

Be sure to check inside ornaments, plant pots, and around your plants regularly for signs of eggs.

For egg buriers, the burial site will typically be marked by an unusual shape within your substrate. 

Again, it’s pretty obvious when you see it. If a certain fish is constantly surrounding an area of your aquarium where these burial sites are, chances are there are eggs inside that they are trying to protect. 

There aren’t many egg burying fish that are found in home aquariums. The most common is the Killifish. 

In this section, I will cover the basics of caring for your fry, regardless of the species of fish and the kind of spawn they produce. 

Because fish fry are so fragile and delicate, you need to know exactly how to care for them to make sure they safely reach adulthood and are as healthy as possible.

The parents can only do so much. Your aquarium is an ecosystem with a lot going on, so you have to be there to assist the parents in raising the juvenile fish. 

Let’s start with discussing housing: 

You typically have three main options when it comes to housing your fry. 

You can either: 

Keep everything all in the same tank.

This is a more natural process, as everything will play out as it would in the wild. The only difference is, you will be feeding them. The upside to leaving things as they are is that it’s less effort on your behalf.

You simply let nature run its course and see how the cards play out. The downside is that you will lose considerably more fry if you were to leave them in the same tank as other fish. You also need to consider environmental dangers such as the filter, water flow, and sharp edges.

Keep them in the same tank, but separated by a tank divider.

By keeping the fry in the same aquarium, you have the added benefit of keeping the water and everything consistent. Moving fry to and from different bodies of water can lead to unwanted deaths due to the subtle changes in water chemistry that aren’t dangerous to adult fish, but are to fry and juveniles.

The divider can keep the fish safe from other fish, and you can decide what section of the aquarium you keep them in, away from any environmental hazards.

The third (and in my opinion the best) option is to install a breeder box.

If you haven’t seen a breeder box before, they simply sit on the rim of your aquarium, providing an enclosed, safe space for your fry to develop, while still being sat in the same aquarium.

You could quite as easily set up a breeding tank to raise the fry, but that comes at extra cost and increased risk. However, if you’re serious about breeding fish, setting up a dedicated tank is something to consider. 

Changes in water temperature, pH, hardiness and ammonia levels are important things to track in every aquarium, regardless of the life inside it. 

When it comes to raising fry, however, the risks of losing them is greatly increased if the water parameters are not optimal and consistent, and if the physical environment is not correctly contained. 

Fish fry have immature immune systems, meaning they are not yet equipped to deal with the hardship of aquatic life. 

Fry are much more susceptible to all kinds of disease (Fungal, bacterial, viral and parasitic). 

Poorly filtered water and constantly fluctuating water parameters are surefire ways to reduce the survival rate of your fry, so it’s important to make sure your water is as stable as possible before even considering breeding.

Here are a few things to consider when raising fry in your home aquarium: 

Test Your Water Frequently

Knowing is the first step to controlling.

You can’t optimize your water if you don’t test it regularly. Be sure to test your water at least weekly to note any changes in water chemistry. Ammonia levels must be zero.

Do frequent water changes.

Water changes are the best way to control the ammonia levels in your aquarium. However, too big of a water change can throw off the parameters for a short while.

That might not be an issue with your adult fish, but for fry, any changes can be fatal.

I recommend changing your water by 10% every 2 or 3 days. For smaller tanks, more frequently will serve you better.

Maintain Consistent Temperature

The fry will be fine in the water temperature that its specific species prefers, whatever that may be. It’s not necessarily the temperature itself that’s the issue, it’s the fluctuations.

Simply check what the optimal temperature is for the specific fish in question and use a thermometer to make sure it stays stable.

Calcium is super important.

A lot of fish will not absorb calcium from their food, but rather from the water itself.

A good rule of thumb for calcium levels is around 20 parts per million. You can test water calcium levels using a simple calcium test kit. Too much calcium can lead to issues in your aquarium, so testing for it regularly is a good idea anyway.

There are also several environmental hazards that you will need to be wary of. Here are a few pointers to keep in mind: 

Good Filtration Is Key (But Not Too Fast)

Good filtration is obviously a crucial part of maintaining stable water conditions, but not all filters are the same. The amount of flow (water movement) can be an issue for young fry if it’s too high.

Also, the filter intake can easily swallow up your fry if it has an open-ended source. Sponge filters are the perfect filter for aquariums with fry. They keep the water clean while eliminating the risk of your fry being sucked into their demise. If you don’t have a sponge filter, simply cover the intake with a piece of sponge.

Watch Out For Other Fish

Fish aren’t fussy eaters. If it’s small enough to go in their mouth, they will give it a try. Fry and juvenile fish are not even safe around their own parents.

It’s completely normal for fish to eat their own fry. That’s why breeding boxes are so useful. They keep the fry in the same aquarium, but outside of harm’s way.

Provide Plenty Of Plants and Hiding Spaces

But nothing too sharp. Lot’s of plants will not only help to keep the water oxygenated and clean but will also provide shelter for both the courting couple and the juveniles they rear.