Bristlenose plecos are one of the most popular fish in the aquarium. Bristlenose plecos eat algae, are lively and the many colorful variants make them an attractive choice for both beginners and advanced hobbyists.

On top of that, bristlenose plecos are rather small pleco catfish, making them suited for in many tanks. In this post, you’ll learn everything about bristlenose pleco size.  

How big do bristlenose plecos get?

Bristlenose plecos are often considered small when compared to big species like the common pleco. Yet, they do get bigger than most people claim. 

Bristlenose plecos (Ancistrus) reach full size at a length of around 6 inches, with exceptions growing up to 7 inches big. Some other varieties of bristlenose plecos such as longfin bristlenose plecos stay smaller, usually getting 5 to 6 inches in size.

Males usually become the biggest, with some extremes getting up to 8 inches in size. Females stay a little smaller, around 6 inches at max. 

Whether bristlenose plecos reach their max size depends on tank size, diet and genetics.

Albino bristlenose pleco size

Albino bristlenose plecos grow to a full size of 5 to 6 inches. Some exceptions may even reach a size of 7/8 inches. How fast and how big an albino bristlenose pleco can grow depends on tank size and the food being fed.

Albino bristlenose plecos are very similar to common bristlenose plecos: they get around the same size and need the same care.

An albino bristlenose pleco male. Photo by Thomas Siems

Starlight bristlenose pleco (L183) size

Starlight bristlenose plecos grow on average about 4 to 5 inches big. Ancistrus dolichopterus is a smaller species than the common bristlenose pleco (Ancistrus cf. cirrhosus) that grows up to 6 inches.

Do bristlenose plecos grow to the size of their tank?

Many sites claim that bristlenose plecos only grow up to 5 inches big. As stated above, this is not correct. But how is it that many bristlenose plecos stay this big when they can become way bigger?

To a certain degree, a bristlenose pleco grows to the size of their tank. When being kept in a tank too small, a bristlenose pleco will stay smaller and stop growing. Males will usually stay up to 3 to 5 inches when being kept in a smaller tank.

Bristlenose plecos are often sold at a very young age and small size, of 1-2 inches and at age of 2 to 3 months old. This makes it look like it’s a very small species, suited for almost all tank sizes. When a small pleco like that is put in a small tank, it will not grow as big or fast as it could.

This doesn’t mean that it’s good for the pleco to be kept in a small tank, to limit its growth. This isn’t healthy, nor a good way to keep fish. A bristlenose pleco should always be kept in a spacious tank.

How to make bristlenose plecos grow bigger

Many bristlenose plecos stay small, only because the owner has been wrongly informed about the care of this beautiful fish. In order to make them grow to their full size, some things need to be met.

There are three important aspects for the growth of a bristlenose pleco: tank size, filtration/water changes, and the right diet. In order to make them grow big, a 25-gallon tank with a strong filter is needed and a varied diet should be fed.

The first thing to consider is tank size. In order to grow to its full size, bristlenose plecos need a tank of at least 25 gallons. There are people who claim they can live in a 20-gallon tank, but I’ve found that this slightly territorial fish will need more space to feel comfortable.

After the tank, it will need to be well filtered. Plecos produce a lot of waste, and thus a good filter is needed. On top of that, it’s recommended to do regular water changes to further promote the growth of the bristlenose pleco.

A well-balanced diet is necessary for any fish and certainly for bristlenose plecos, who are often thought to only eat algae. This is not true, and bristlenose plecos are omnivores, that prefer a more plant-based diet with some meaty foods added. Feeding bristlenose plecos vegetables, high-quality pellets, and occasionally some high-protein meaty foods.

As a rule of thumb, around 80-90% of a bristlenose plecos diet should consist out of plant-based foods. Driftwood for plecos is also something to consider. This will make sure the pleco gets all the nutrients it needs to grow big.

Bristlenose pleco growth rate

You might have bought a small bristlenose pleco in the pet store, but how fast will that bristlenose pleco grow to its full size?

The first year of its life, a bristlenose pleco will grow the fastest and it will grow up to 1 inch in the first 2-3 months. After 2 to 3 years it will have reached its full size, at around 6 inches. How fast bristlenose plecos grow depends on water changes, food and tank size.

After the first two to three years, the growth will start stagnating. However, most fish will keep growing at a very slow pace for many years to come. If you consider the bristlenose pleco’s lifespan is up to 20 years, it’s not weird to think that in extreme cases, bristlenose pleco males can be up to 8 inches long.

How to make bristlenose plecos grow fast

Breeding bristlenose plecos are very exciting, but the real work starts when the fry has come out of the male’s cave.

The biggest factors in fry development are nutrition and water quality. To make fry grow fast, more water changes should be done and high nutrition, high-quality foods should be fed.

  • Tank setup – It’s recommended to put the babies in a separate tank. This way there’s no competition for food and the tank can be kept cleaner. A tank of at least 15 gallons is recommended for raising fry.
  • Filtration – Bristlenose pleco fry produce tons of waste. When you are feeding the fish heavily, the water parameters will decrease drastically if the filter is too weak, resulting in slower growth.
  • Water changes – In addition to a strong filter, regular 50% water changes should be performed. Preferably every other day.
  • Nutrition – A varied nutritious diet is very important for pleco fry. This should consist out of plant-based foods. As the fry gets older, some meaty foods can be added. 
  • Water temperature – Generally, pleco fry will grow faster in warmer water, because this boosts their metabolism. If you increase the temperature, you will need to pay extra attention to filtration and make sure their is enough oxygen in the tank. The best water temperature for plecos
Photo by Max Wei on Flickr

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Bristlenose plecos are a relatively small species, which makes them ideal for many community tanks. Nonetheless, they’re not as small as many people claim and reach their full size at a length of around 6 inches. The starlight bristlenose pleco stays smaller, getting around 4 to 5 inches.

In order to let bristlenose plecos grow to their full size, a 25-gallon tank is needed, with the right filtration and a proper diet. the same goes for raising fry fast. With a strong filter, well-suited tank, and proper nutrition (mostly plant-based foods) fry will grow the fastest.

The first year of their life, a bristlenose pleco will steadily grow the fastest. After this year, growth will stagnate. They reach full size at 2 to 3 years.