How to Increase Guppy Fry Growth Rate?

Guppies are easy to breed and it’s fascinating to watch them morph from fry to adult. You never know what these little fish are going to look like once they reach maturity.

But seeing them transform and gain color day after day is a big part of why they’re so fun and interesting. Many guppy fish owners can attest to how satisfying this entire process is.

Of course, it’s not always easy to meet a growing fry’s needs. Many new guppy owners are struggling to manage their newborn fish. If your Guppy Fry have trouble growing, you have to do some tweaking to get them back on track. So, if you’re looking for ways to increase your guppies’ growth rate, this article is for you! I’m going to outline all of the reasons and solutions to your fry-growing woes.

Why Are My Guppy Fry Not Growing?

First, let’s talk about the most probable causes. If your guppies aren’t developing properly or at the usual rate, something might be lacking. Whether it’s a nutritional deficiency or an environmental cause, the main issue needs addressing.

The most likely reasons for your fry’s stalling growth include a poor diet, bad water, lack of hygiene, too little or too much light exposure, and too much or too little space. Let’s look at each of these cases in further detail. I’m also going to explain how these factors play into your fry’s development.

– Poor Diet

Adult guppies are sturdy and adaptable. They can live off of dry food such as fish flakes without issues. But Guppy Fry are still developing. They need a variety of high-quality foods to meet their nutrient needs and then some. They don’t just need food to cover their bases. On top of sustaining their daily life, they also need it to grow their bodies.

Without proper nutrient intake, they won’t grow to their full potential. Also, a monotonous diet won’t provide all the vitamins and pigments needed to color their bodies. Poorly fed fry will remain small, dull, and they might even grow deformed. The spine is the last body part to fully develop in young guppy fish. A lot can go wrong if they’re not fed a nutritious diet throughout this long process.

– Bad Water Quality

Water quality could include a variety of factors. Dirty water, water that’s too soft or too hard, and water that contains harmful chemicals could all negatively impact your fry’s health and growth. When waste and toxins accumulate in the water, your fish are at risk of developing infections, ammonia poisoning, and burns.

Proper water hardness and pH levels are also crucial for your fry’s immune system and development. Even if these issues are caught in time, your little fish will still work overtime to adapt to the initial unsuitable living conditions. Sudden changes in water quality might also stress your fish. Their immune system might go into overdrive, and this consumes a lot of energy that could otherwise be used for growth.

– Unsanitary Conditions

I can’t stress enough how important hygiene is for the health and development of your guppy fish. We already know that exposure to pathogens can cause sickness and hinder growth in small fry. But dirty water isn’t the only source of harmful bacteria and toxic waste by-products. Nothing in the tank is safe.

If you neglect the tank walls, decorations, and substrate, bacteria can still spread even with water changes and filtration. Besides stunted growth, you should also look out for other signs of bad health. Loss of appetite, lethargy and lack of movement are symptoms of poisoning and should not be ignored!

– Too Much or Not Enough Light

Guppy fish rely on external cues to regulate their sleep cycle. When the lights are out, guppy fish go to sleep and their breathing slows down. When the lights are on, they are active and their appetite increases. Guppies need both light and darkness to develop and maintain their health. But you need to strike the right balance.

Too much light exposure might disrupt your fry’s sleep, which will impact their growth. Sleep is when growth and cell repair happen, after all. In the worst-case scenario, too much light exposure can even lead to death! Too little light exposure will lead to spine deformities, lethargy, and lack of appetite, and you don’t want that either.

– Too Much or Not Enough Space

Not enough space can be harmful for two main reasons. First, cramming a bunch of fry into a small space is a sure-fire way to expose them to bad bacteria. The more fish there are in the same space, the faster the waste accumulation.

Second, when the fry are all bunched up in the same space, it’s hard to ensure they’re all feeding properly. Some of the fry might be getting too little food when the other fish get competitive. When all the fish rush to the surface to feed, they might also hurt each other in the process. So, if too little space is so bad, you might be tempted to go to the other extreme.

But too much space might also pose a risk. Your fish don’t catch everything you feed them right away. Some food will settle down to the bottom of the tank. If there’s too much space, the little fish might have a hard time finding the food leftovers. As a result, they won’t be getting enough nutrition and they’ll also expend too much precious energy foraging.

How to Make Guppy Fry Grow Faster?

Now that we’ve covered all the things that could go wrong, let’s start shining rainbows on this show. There are many solutions to these problems and there’s no shortage of things that can aid your guppy fry’s growth. Some of these you might already be doing. You don’t have to follow these instructions to a T.

Depending on the number of guppy fry you have, and their stage of development, some tips might not apply. For example, newborn guppy fish are very sensitive, while older fry can adapt to harsher conditions a bit better. But good hygiene, proper diet, and a suitable aquarium set-up are all indispensable for small fry and adult guppies alike. So, let’s see. What could you do to improve your guppies’ growth?

– Fix Their Diet

Feed your guppy fry a wide variety of foods. Give them a combination of dry food, fresh food, even live food if you have access to it. Nutrient-dense foods such as brine shrimp, daphnia, infusoria, and dried bloodworms should make up a large part of their diet. However, you shouldn’t feed your fry a lot of food. Overfeeding is counterproductive and dangerous. Focus on nutritious, high-quality food, and don’t go overboard on portion size.

Plankton and algae-based pellets are also good sources of vitamins and minerals which are crucial for development. Young guppies need protein and plant foods to develop and gain color. With regards to frequency, you should feed them 3-5 times a day. Make sure that your feed is small enough for them to eat.

– Provide Enough Space

Your fry need enough space to feed and exercise without disturbing one another. For newborn fry up to a month of age, I’d say half a gallon (or 2 liters) is enough water volume for each fish. But you’ll have to increase this space as the fish grow.

Guppy fry older than one month will need at least one gallon (4 liters) of volume per fish. So, if a 10-gallon aquarium could initially fit 20 guppy fry, once they grow larger, you’ll have to double your aquarium size. Good filtration and frequent water changes could increase your limit of fish per tank, but that still won’t solve the feeding issues.

– Improve Water Quality

The first thing to remember is to change the water at least once a week. However, with younger guppies, I’d suggest changing the water more frequently. Depending on how many fish there are in the tank, and on how often you feed them, you might have to change the water more or less often.

You might get away with two smaller water changes each week (around 15-20%) if you feed your guppies just 3 times a day. Frequent feeding, around 4-6 times a day, will require additional work. If you feed your guppies more often, try at least 3 small weekly water changes. Note that installing a filter won’t save you from changing the water! However, a filter is still very useful to keep your fish healthy.

– Respect Water Parameters

Speaking of water quality, you should also ensure that your aquarium water meets certain parameters. Most importantly, you should keep the water at a pH of around 6.8-7.8. As long as you aren’t specifically buying alkaline water, most sources should fall within this range.

However, depending on where you live, tap water pH can range between 6.5-8.5, and sometimes it might go as low as 4.4-5.3, which is too acidic for your fish. You should always check with some pH test strips just in case.

Water hardness is not as important, but you should still try to keep it in the optimal range of 8-12 dGH, or 142-215 ppm. You might have a hard time finding hard water in your area. In that case, you can use either a water hardener or a water softener to reach these figures.

Another crucial thing to remember is to condition your water, especially if you’re using tap water for your aquarium! Chlorine, chloramine, nitrites, and nitrates in drinking water are bad for your fish, even if they’re within a safe range for human consumption. That’s why you want to treat your water with a high-quality conditioner before you expose your fish to it.

One last thing to remember is to avoid sudden fluctuations in water parameters. This might shock your fish and cause unwanted side effects. To play it safe, you should choose one main source of water and stick to that. If you’re considering a change, always perform some tests beforehand and don’t switch sources too often.

– Keep Temperature Within the Suitable Range

The ideal temperature range for growing guppy fish is 75-78 °F (24-26 °C), although they can also live in wider temperature ranges of 65-85 °F (18-30 °C). I’d suggest sticking to a narrower temperature range. For optimal health and growth, keep the temperature constant and avoid fluctuations.

As with the sudden change in water parameters, sudden fluctuations in temperature might shock your fish and affect their immune system. If the temperature in your room fluctuates a lot, you should install an aquarium heater and a thermometer. That’s the best way to efficiently monitor and regulate temperature changes.

– Provide Enough Light Exposure

Guppy Fish need about 12-16 hours of light exposure per day. This helps them to stay active, and it upregulates appetite and metabolism. All these factors are important for proper development. You shouldn’t keep the lights on for longer than 16 hours per day though.

Definitely don’t let the lights on 24/7. Constant light exposure can be too much of a good thing. While light is crucial for guppies’ health, your fish still need some sleep. Turn the lights off at night to allow your fish at least 6-8 hours of sleep.

– Don’t Expose Fry to Strong Water Flow

You don’t want stale water, so filtration and water movement are still important. However, you don’t need a strong internal filter. Strong water currents might be too much for your small fry to handle. Because they aren’t fully developed, they have a harder time swimming against the flow.

This makes them exert too much energy and it also makes foraging more difficult. An air-driven sponge filter should do the job just fine, without creating such a strong flow. Even for larger-sized aquariums, a sponge filter should generate enough water movement.

– Separate Fry from Adult Guppies

If you want your fry to grow big and healthy, the first step is to not let them get eaten. For some reason, adult guppy fish tend to eat their young, especially if they’re newborns. Actually, guppy fish tend to eat anything that fits in their mouth. Not that this information makes things any better.

When fry and adult guppies share the same tank, the little fish will spend most of their time hiding. This means a lot of lost opportunities to eat properly. Also, when the bigger fish get competitive for food, the little guys won’t stand a chance! It’s very stressful for them to fight for food and to be in constant danger of being eaten.

– Separate Males from Females

After the first three months, your guppy fish will reach sexual maturity, which means they’ll start breeding. Not only is this activity energy-intensive, but gestation is also draining for female guppies. Breeding has also been correlated with a shorter lifespan for guppy fish. To help them conserve their energy, you might want to keep male and female fish in separate tanks.

You won’t be able to distinguish their genders until about 3 weeks of age. Look for colorful fish with wider, longer tail fins. These are clear sexual characteristics of a male guppy. Females are less colorful, but larger in size. At the same time that male fish start developing vivid colors on their tail and abdomen, the female guppy fish might develop a gravid spot on her belly.

– Separate Fry By Their Size

Not all fry grow at the same rates. Maybe you also have two-month-old fish and newborn guppies. I’d suggest keeping them separate. Usually, the bigger the fish, the faster and the more agile they are. They tend to eat all the food before the smaller fry can feed. As a result, the small fry will stay small and undernourished, while the larger ones will keep growing.

You may think that growing fry in one tank will incentivize them to compete and grow faster. But that’s not entirely true. When there are big differences between the fry, the big ones will get all the food, while the small ones will likely die. I strongly recommend you separate the fry based on their size. This adds efficiency to the growth process, and it’s something I personally tested.

– Use A Grow-Out Tank

A grow-out tank is a tank specifically devised to help fish grow. It doesn’t have anything special other than being separate from your other aquarium. The fry will be able to grow healthily and optimally without being hindered by adult guppies. From my experience, a grow-out tank for freshly-born fry is a necessity, as it can greatly improve the growth rate.

– Keep The Tank Clean

I can’t begin to describe how important a clean tank is. Performing weekly water changes, changing the gravel, and cleaning the filter will ensure your fry grow at an optimal pace. By changing the water weekly, you eliminate all the accumulated toxins, especially if you feed the fry more often. You can do smaller water changes (about 15-20%), or bigger ones.

But that’s far from enough. You also need to clean the gravel and the filter. They can gather a lot of muck, parasites, filth, and toxins. Just look at the bottom of the tank, if you use bare-bottom aquariums. You should notice the fish waste building up in the substrate, and it’s not looking good. Even if you can’t see it, this means it’s under the gravel. It’ll pollute the water until you do something about it. Clean your filter and gravel periodically so the fry live in a healthy aquarium!

– Use Some Live Plants

Do you know why expert fish keepers recommend adding live plants to the aquarium? It’s not only because guppies are more comfortable with hiding spaces around them. Live plants also consume the nitrates from fish waste and transform them into beneficial bacteria. They purify the water, allowing fry to grow optimally.

Guppy fry also enjoy grazing on grass, which means they get extra meals without you feeding them. Live plants are also breeding grounds for beneficial microorganisms and algae. Personally, I keep java moss, java fern, and guppy grass in my main tank and the out-grow tank. The guppies and fry enjoy the hell out of those plants. What’s more, these plants don’t need any artificial lighting or fertilizers, as they grow naturally without your intervention.

– Watch Out for Bacteria and Parasites

You never know when the tank becomes the breeding ground for a nasty parasite. Fry can get genetic disorders from their parents. They’ll breed, and the offspring have the same problems. Or you introduce new fish to the aquarium, and they bring parasites with them. Fry are most vulnerable to external threats, and the parasite may even wipe them out completely.

Perform regular water changes, provide quality food to your fish, and quarantine new fish for 3-4 weeks before introducing them to the main tank. I recommend inspecting the fry periodically for any anomalies. Did any of them die in strange circumstances? Well, it may be worth investigating because it could be a parasite beginning its feast. Watch out for bacteria and parasites!


To sum up, there are quite a few things you can do to increase the guppy fry growth rate. This guide should provide a helping hand in identifying the right elements you can use to do this. I recommend getting a second tank to use as an out-grow aquarium for the fry. Adult guppies are known cannibals that constantly eat fry, and even guppy mothers do that. And getting eaten doesn’t exactly help with survivability or growth.

Then, there’s the entire thing about water quality, light exposure, a proper diet, the presence of parasites and toxins, and much more. Consult the points I mentioned for every category and implement those you find useful!

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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