How big do guppies get? On average, male guppies grow to approximately 0.6″–1.4″ (1.5-3.5cm) and female guppies grow to approximately 1.2″-2.4″ (3.0-6.cm) long. Actual adult size varies according to a number of factors including diet, water quality, and genetics.
Guppies are one of the most widely kept tropical fish in the freshwater fish-keeping hobby. I first kept a tank of guppies 30 years ago, when I was given a 10-gallon aquarium with a handful of guppies, and I have been completely hooked on them ever since. I have bred guppies for fun, for competition and to sell for profit.
It is easy to see why guppies are loved by both new and experienced fishkeepers alike. The fact that we can keep and breed such a colorful, hardy, and friendly fish still amazes me today.
What Helps Guppies Get To Full Size?
For guppies to reach their full size they need a number of factors to be right.
- Diet: Guppies are omnivores. As such they need a diet based both on plant and animal matter. Getting a balanced, varied diet ensures they get all the right vitamins and minerals they need for healthy growth. As aquarists in the 21st Century we are extremely lucky. There are dozens of different types of flake food or mini pellets we can feed our guppies that will deliver that well balanced diet they need. Add some live or frozen food into the mix and you can be sure your guppies will grow large and strong. A poor quality diet will undoubtedly have an adverse affect on your guppies growth. I recently wrote an article titled What Do Guppies Eat? which has good advice on the best foods to feed guppies for optimum health and growth.
- Water Quality: Good water quality promotes proper fish health and growth. Carrying out regular water changes promotes good quality water. Studies have shown poor water quality has an adverse effect on guppy growth. A study in 2014 showed that water with high levels of nitrates affects fish growth due to less haemoglobin transporting oxygen around the body. High nitrates can be caused by overfeeding, too many fish in the tank and lack of water changes.
- Separating the sexes: Raising male and female guppies separately can help females attain their true potential size. As a live bearing species of fish, guppies breed easily. If females become pregnant at a very early age, their growth can become stunted. Keeping them separate from the moment you can tell the sexes apart will reduce the chance of the females becoming pregnant.
- Genetics: If guppies are bred from good quality stock, the chance they will grow into big and strong guppies themselves is higher. If you are breeding your own guppies, try to only allow the biggest, brightest, strongest guppies to spawn.
What Prevents Guppies Getting To Their Full Size?
There are many factors that prevent guppies from reaching their full potential. These may include:
- Poor Diet: Not feeding guppies often enough, or feeding them poor quality foods will cause guppies not to reach their full size. Guppies need to be fed 3 or 4 small meals a day. These meals should be made up of a variety of foods to ensure they receive a balance of vitamins and minerals. Avoid feeding your guppies very cheap fish foods as they often contain ‘fillers’ which offer your guppies no nutritional benefit.
- Poor Water Quality: As mentioned above, poor water quality, essentially water with high levels of nitrates, will stunt the growth of your guppies. Overfeeding your guppies, keeping too many guppies in an aquarium and not carrying out regular water changes can all cause nitrate levels in an aquarium to be too high.
- Overbreeding: Female guppies can become pregnant at 2 to 3 months of age. Once pregnant, the female will put all her energy into producing baby fish. Her growth rate will slow considerably and she may well end up stunted. To prevent stunting females, raise the sexes in separate aquariums, dividing them the moment they can be reliably sexed.
Does Aquarium Size Affect Guppy Size?
Yes, aquarium size affects guppy growth, but not in the way people think. The popular myth is that fish only grow to the size of their aquarium. The reality is, keeping a group of guppies in an aquarium that is too small will almost certainly lead to poor water quality due to the build-up of nitrates. High nitrate levels will stunt the growth of the guppies.
To reduce this problem, you not only need to think carefully about the number of guppies you put in your tank initially, but also the consequences of their almost infinite desire to reproduce. Think of ways you can keep your guppy numbers down.
Maybe consider keeping just males, or adding a micro predator that will consume some of the baby fish to help keep the numbers manageable.
A single fancy goldfish in the aquarium with the guppies (yes, guppies and fancy goldfish can live together!), will help keep the population under control, as will adding an African Dwarf Frog.
If you don’t like the thought of the babies being eaten, have a conversation with your local fish store. They may be only too happy to swap your excess baby guppies for some frozen food or maybe something else from their store. Talk the problem through with them, there is usually a solution.
My article How to Control Guppy Population has some great suggestions to prevent the number of guppies in a tank from getting out of control.
There are many factors that affect guppy size and growth rates. Feeding your guppies a high-quality diet, carrying out regular water changes, and not overcrowding your aquarium will all help ensure your guppies reach their full potential size.
A female guppy pushing nearly 2” (5cm) in length is an impressive fish. It is well worth the time and effort to raise a batch of females in a separate aquarium to the males.