Bristlenose plecos (Ancistrus) are popular algae-eating catfish that are much smaller and easier to keep than common plecos. Discover how to care for bristlenose plecos, including tank size, water parameters, feeding, behaviour, compatibility and breeding.
Algae eaters. Every fishkeeper has likely asked for one from their local fish shop at some point during their time in the hobby. Previously, you'd walk around shops and see tanks filled with common plecos, pictured below, which is a name that has been used for several species. Fishkeepers would happily take them home, expecting the fish to happily graze on algae and not cause any issues.
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However, after taking home a common pleco, algae is no longer the fishkeeper's biggest concern. These suckermouth catfish grow big, really big. They can reach over 50 cm (20 in) in length depending on the exact species you have, and the little juveniles quickly put on size in aquaria, meaning they soon outgrow most tanks leaving the unsuspecting aquarist with a tough decision: invest in a larger tank for their pet, or try to find it a more suitable home.
Related article: 10 best algae eaters for tropical tanks.
Enter the bristlenose pleco
These days, you'd likely have to visit a few stores before you found a juvenile common pleco for sale. You might encounter the odd large specimen in a display tank, but this is likely a rehomed individual that is living out its life in the store's care.
Instead, the trade has a new favourite armoured suckermouth catfish to recommend for algae eating, and this one is far more suitable. Bristlenose plecos.
Unlike their larger relatives that outgrow the majority of aquariums, bristlenoses, or Ancistrus, typically reach around 12 cm (4.7 in). Giving a precise maximum size is difficult, as several species are sold under this common name.
What is an Ancistrus?
Bristlenoses are also commonly called Ancistrus, which is actually the genus that these fish belong to. FishBase currently lists 78 scientifically recognised species within the genus Ancistrus. However, the aquarium trade contains numerous additional undescribed forms and regional variants, many of which are known to hobbyists by L-numbers or other trade names. For example, Planet Catfish lists 187 different fish under the Ancistrus genus.
With suckermouth catfish, or loricariids, you'll often see L-numbers being used. The German aquarium magazine DATZ introduced the L-number system in 1988 to give aquarists a way of identifying and discussing undescribed loricariid catfish. Even after they are scientifically described, hobbyists often continue to use the L-number as well.
However, the situation with the common bristlenoses you'll find in almost any fish store is complicated further. Exact species identification for these fish is difficult, they're remarkably similar and without collection location information you'll likely not get very far.
These fish breed in captivity fairly easily, so the majority of the fish you'll find will be tank bred and listed simply as Ancistrus without any information on their origins. Given the long history of captive breeding and the uncertain origin of these fish, it is possible that some of the common bristlenoses kept in aquaria today are hybrids with a mixed ancestry.
That's not necessarily a problem for the fishkeeper. It simply means that when you buy a common bristlenose, you're often buying a hardy, captive-bred Ancistrus of uncertain taxonomic identity rather than a fish that can confidently be assigned to a particular species.
How to care for an Ancistrus
Their modest maximum size and hunger for algae are not the only positives about bristlenose plecos; they're also fairly easy to keep and well-suited to beginner fishkeepers. But even an easy-going fish still has some key care requirements that must be met.
Common bristlenose pleco fact file
Scientific name: Ancistrus spp.
Size: A maximum of 15 cm (6 in) is cited, although they usually remain smaller at 10 to 12 cm (3.9–4.7 in)
Origin: South America, but the exact location varies depending on the species. Most available specimens are likely captive bred and are potentially hybrids
Habitat: Varies between species, but many are associated with flowing, well-oxygenated water and structures such as rocks, roots and submerged wood that provide shelter and grazing surfaces
Minimum tank size: 60 x 30 x 30 cm (24 x 12 x 12 in) for a single fish or breeding pair, but larger would be needed for a group
Water requirements: Slightly soft and acidic to slightly alkaline water; 6.0-7.5 pH, 2-18°dH
Temperature: 22–26°C (72–79°F)
Temperament: Peaceful towards other fish but may occasionally have territorial disputes with conspecifics, which rarely lead to any damage
Feeding: Offer plenty of fresh vegetables, such as cucumber and courgette, along with algae-based wafers and sinking foods formulated for herbivorous fish. They primarily graze algae, aufwuchs and biofilm, and will rasp on surfaces in the tank, such as submerged wood
Availability & cost: Common and available in almost every store. Prices vary depending on type, source and size, and juveniles can be available from as little as £4
Aquarium requirements
Given the modest maximum size of bristlenose plecos, they don't require huge aquariums. A 60 cm (24 in) aquarium will work for a lone fish or breeding pair, but their size and strength can make them a little destructive in smaller aquariums.
Footprint is more critical than volume, especially when housing a group. Opt for a long and wide aquarium rather than a tall one if possible as this allows individuals to establish their own territories.
Decorating a bristlenose aquarium
Given the Ancistrus you'll likely be buying is captive bred, there's no need to go down a biotope route for the decoration of their tank. A standard community setup with a bit of wood and a few rocks over an inert substrate will suffice just fine. Just be sure to position the wood and rocks in a way that creates a few shaded overhangs or caves.
If you aren't able to create suitable hiding places for your bristlenose, or are keeping a group and need to add a few extra (always worth having more caves than catfish) then ceramic catfish caves work great! Also consider using natural botanicals as caves, there are some great options available!
Adding live aquarium plants is certainly possible, but there are a couple of considerations to keep in mind.
- Delicate stem plants and newly added plants can be uprooted by the bristlenose's movements. Get them established before the Ancistrus are added, or skip them altogether in favour of more robust species.
- Broad leaved plants like Amazon swords (Echinodorus) can sometimes be too tempting for bristlenoses. Small holes in the middle of the leaves can be a sign that your pleco is rasping on these leaves.
Related article: 5 easy and beautiful stem plants.
Water chemistry
Bristlenose plecos are fairly adaptable to a range of water parameters. Aim for stable conditions within their normal tropical range rather than trying to replicate a particular set of numbers. Aim for a pH between 6 and 7.5, although up to 8 is usually acceptable. A water hardness below 18°dH is generally suitable.
They are a tropical fish, not a temperate species, so you will need a heater. Set it in the range of 22-26°C (72-79°F) depending on the requirements of the other species in the tank.
The one thing that is probably most often forgotten for bristlenoses is their fondness for water flow. They chiefly come from flowing, oxygenated streams and rivers and, as such, enjoy some water movement in the tank. They don't need a torrent-like flow, but a suitably sized filter positioned to provide plenty of surface agitation, and therefore oxygenation, will definitely be appreciated.
Behaviour and compatibility
In general, species from the genus Ancistrus are peaceful and tend to keep themselves to themselves. They rarely bother their tank mates and will often coexist happily with shoaling fish occupying the upper and middle areas of the aquarium. Many aquarists have even kept them alongside freshwater shrimp colonies, with some baby shrimp surviving in well-established, densely planted aquariums.
The main source of aggression in bristlenose plecos is territorial behaviour, particularly when males compete for suitable caves in which to breed. Males can defend these shelters against other similar cave-dwelling species, and territorial disputes may become more pronounced when suitable hiding places are scarce.
As a general rule, providing more caves than there are fish can give less dominant individuals a greater choice of shelters, although the exact number required will depend on the species, tank size and individual fish.
Feeding bristlenose plecos
Many aquarists wrongly assume that all suckermouth plecos only eat algae or other plant-based foods. This isn't the case across the Loricariidae: different plecos have quite different dietary adaptations. Ancistrus, however, are primarily grazers of algae, aufwuchs, biofilm and associated organic matter, making them much more herbivorous than many other plecos.
In aquaria, relying solely on naturally occurring algae can therefore leave a bristlenose without enough food, particularly in a clean or relatively new aquarium. Algae growth and biofilm production can also vary considerably over time. This is why it is important for fishkeepers to offer their bristlenose plecos plenty of supplemental food rather than expecting them to survive on the algae growing in the aquarium alone.
Fresh vegetables such as cucumber and courgette work well as supplementary foods, as do good-quality algae-based wafers and sinking foods formulated for herbivorous plecos. Small amounts of more protein-rich foods can be offered occasionally, but these shouldn't make up a major part of an Ancistrus' diet.
Related article: Getting the greens in the catfish.
Breeding Ancistrus and sexual dimorphism
Breeding Ancistrus is relatively straightforward, as long as you have both males and females.
Mature adults are easy to differentiate as males display a rather striking beard of bristles around their head and mouths. Females may have a few very small bristles but these are restricted to around the mouth and never up the nose and onto the head as they do in males.
Juveniles are difficult to sex until they begin to mature, usually when they reach around 6 cm (2.4 in) in length. If they start showing bristles developing up the head, between the eyes, this is a good indication that the fish is a young male.
Males also have a wider head when looked at from above, whereas females' heads blend more seamlessly into the body. Again, this difference is generally much easier to see in mature fish.
If you want to breed bristlenoses, mature pairs are sometimes available in stores. Otherwise, it is usually best to buy a small group and allow a pair to form naturally, rehoming surplus adults with friends, fish stores, or through hobbyist auctions if you cannot keep them all.
With a mature male and female present in a tank, spawning is incredibly likely. The male will guard a suitable cave and attempt to attract a female. If successful, she will enter the cave to spawn. You are unlikely to witness much of this, and the first sign of eggs will be the male fanning his fins inside the spawning cave. He does this to ensure they receive a good supply of oxygenated water.
Male bristlenose plecos are usually good fathers and, unless disturbed or spooked, will generally guard the eggs diligently. The eggs are usually orange in colour, and the number of eggs in the clutch varies considerably depending on the size and maturity of the female.
Eggs typically hatch after four or five days, although this varies with temperature, and the male will guard them for up to another 48 hours while they absorb their yolk sacs; again this is temperature dependent. At this point the young start to leave the cave and look for food. Make sure they have some fresh (ideally soft) veg to tuck into, though they may also accept some finely crushed up dried food and they'll also consume some naturally occurring foods in mature tanks.
In a community tank, some fry will often find enough food naturally to survive, although success will vary depending on the other inhabitants. This is not necessarily a problem, as Ancistrus can spawn readily once a mature pair has formed.
However, before you go ahead with breeding bristlenose plecos, it is worth thinking about what you will do with all the offspring. As they are relatively easy to breed, many fishkeepers are likely to be doing the same. This means common bristlenose plecos can be inexpensive, and local supply can sometimes be greater than demand.
If you do want to breed Ancistrus, you could consider working with a less common species or an established captive-bred colour variety. Starlight bristlenose plecos are a particular favourite of mine, although they do grow larger than many of their relatives, and varieties such as super red and lemon blue eye bristlenose catfish are also incredibly popular in the hobby lately. However, rarity and demand can change, so there is no guarantee that any particular variety or species will be easy to sell.
Think twice before you buy a bristlenose
Species of the genus Ancistrus are certainly a wonderful group of fish, but you might want to reconsider buying one if you are looking for a fish that will simply clean your aquarium for you.
Many aquarists only want them for their algae-eating habits, but this should not be the sole reason for purchasing them. These fish need targeted feeding, just like any other fish, and while they will graze on algae and biofilm in the aquarium, they are not an excuse to ignore your normal aquarium maintenance. Instead, read our guide on 10 ways to beat algae for a more complete way to tackle your algae problem.
They are also fairly cryptic, spending much of the day tucked away out of sight. For many aquarists, this is part of the appeal, as it generates excitement when they do emerge. However, for others, buying a fish and then rarely seeing it can seem like a waste of money and valuable stocking space.
Also, while breeding is relatively easy, it can be challenging to rehome all the subsequent offspring. So, if you are looking at this and seeing pound signs, you'll likely be disappointed. They aren't going to help you quit your day job, but breeding them can be a rewarding project for a novice fishkeeper who wants to learn the ropes of raising fry.