Guppies aren’t exactly known for being the biggest fish in an aquarium.
Guppies that are happy and healthy, given a quality diet with plenty of water to live in, have the potential to get up to 1.5 inches, 2 inches, and sometimes 3 or 3.5 inches in length.
Average guppies, though, generally come in around an inch to 1.5 inches in length. That’s what you’re going to want to focus on when you are calculating how many guppies you can fit in an aquarium (based on the water volume you are working with).
Breaking Down the Guppy Growth Cycle
Understanding the growth cycle for guppies goes a long way towards helping you figure out exactly how big your mature, adult fish are going to be.
Let’s run through the different stages of life for guppies right now!
Early Fry Stage
Baby guppies are “live born” in a stage where they are called “fry”.
Tiny at birth – we are talking about maybe ¼ of an inch long (if that) – you’re going to have to look pretty close when these fry start releasing from their mothers.
After a couple of hours their body straightens out and they begin to feed. These little fish get pretty hungry, so you’ll want to make sure that they are getting plenty of protein rich food – especially in the early stages of their development.
Baby brine shrimp and little bits of hard-boiled egg yolk are a great way to power up your fry guppies.
It’s also important to make sure that the fry guppies are getting a lot of light (anywhere between 12 and 16 hours a day) if you want to maximize their growth potential.
Juvenile Development
The juvenile stage for guppies begins about 30 days after they are born, and this is when they start to get to be anywhere between a quarter of an inch and three quarters of an inch.
Female juveniles are typically a little bit larger than males, and you’ll start to see coloration breakout in your juvenile fish to help better distinguish their sex as well. Male fish are much brighter and almost luminescent compared to female guppies.
Remember to make sure that these baby guppies are getting plenty of food during this stage, too.
Young Adults
The young adult stage begins a couple of months after the juvenile stage, and this is where you’re going to start noticing your guppies becoming more sexually active.
If you don’t want a lot more guppies it’s a good idea to separate the male population from the female population!
The diet of young adults needs to be adjusted a little bit as well. You want to dial back their overall fat intake and instead up the amount of proteins and greens that you are giving them. Brine shrimp are still a go to source, though plankton pellets should be worked into the mix as well.
Mature Adults
Guppies become “mature adults” around the six month stage of their lives. This is when they are going to be anywhere between 1 inch, 1.5 inches, and 2 inches (or more) in length.
By the time six months have gone by you’ll have a pretty good idea of just how big your adult guppies are going to be.
Male guppies might get a little more extension when it comes to their fins and their tails (dependent entirely on their genetics), before the most part growth is going to come to a stop.
It’s time to start varying the diet that you are dropping into the tank. Flake based diets with plenty of brine shrimp and lots of greens will help keep your adult guppies happy and healthy.
Don’t be surprised if your guppies live anywhere between two years and five years after they hit the adult stage, and maybe even a little longer than that. It really depends on how well you keep up with tank maintenance and their care.
Key Factors That Influence Guppy Growth
A bunch of different things are going to conspire to determine just how big (or how small) your guppies are.
Aquarium Size
For starters, the amount of aquarium space that a guppy has to live in is a huge determining factor on how big or how small they get.
A lot of space allows guppies to grow to the maximum of their genetic potential. Limited space, though, will stunt growth and cause guppies to fight over resources – stressing them out and shortening their lifespans along the way.
Water Quality
Water quality needs to be dialed in to keep guppies happy and healthy.
Not only do you need clear, clean, and well oxygenated water (your filter should be rocking and rolling on a regular basis) but you also need to maintain tank water temperatures of between 74°F and 82°F consistently.
Hotter water than that will dramatically increase the metabolism of your growing guppies, expending a lot of extra energy and crippling their growth rate. Colder water will cause their metabolism to plummet and stunt their growth as well as cause a whole host of other health problems.
Keep on top of your water!
Population Size
Population sizes should be based on the amount of water volume in your tank, giving each fish at least a gallon of water for every inch of fish in the tank.
Overpopulation will cause stress not just to the growing guppies but every other fish in the tank as well.
Under population can be a problem too, especially when guppies are young. Guppy fry need to be able to eat food efficiently and they might not be able to if they have to search a lot of water volume to get their meals.
Guppy Genetics
Guppy genetics are going to play a huge role in just how big your fish actually get.
Some guppies have genetics that allow them to grow to almost monstrous sizes (for guppies), reaching 3 inches or longer in length. Other guppies, even with a perfect diet, plenty of room to grow, and perfect water conditions are only ever going to get to be an inch or so in length.
Genetics are something you really can’t influence, either.
You just sort of have to roll with it!