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Do pleco’s and bristlenose’s need wood? Pseudoxylovory in Loricariidae

This is a commonly mentioned topic when it comes to pleco’s, it is a bit of a telephone game over time even since many scientific studies have disproven it. There are three aspects to cover here can they digest it, do they need it for digestion and does wood have other benefits?

Figure 1: *Panaque schaeferi* at Maidenhead Aquatics Ascot

The Background

Loricariids are a group of around 1,080 currently accepted and described species according to Eschmeyer’s Catalog of Fishes, they are endemic to Central and South America. While common names within this group are unreliable it generally includes pleco’s, whiptail catfishes, oto’s, bristlenoses etc. Here in this article I am focusing on a subfamily known as Hypostominae, this includes some of the pleco’s (the most popular ones) and bristlenose pleco’s (Ancistrus, which is nested well within).

Figure 2: *Pterygoplicthys joselimaianus* at Maidenhead Aquatics Ascot.

Some Loricariid genera were observed to gouge on wood using their jaws, Loricariids do not suck their food unlike the name suckermouth catfish suggests. They use a pair of oral jaws and basically rasp at it (Adriaens et al., 2009), which is then further processed by some pharyngeal jaws (a second pair of jaws) who often contain small teeth (Bentley et al., 2026). These paraphyletic genera displayed spoon shaped teeth (Fig. 1; spoon shaped) not found in other groups (Fig. 2).These teeth are unique within Loricariidae for being able to gouge into the wood and often mineralised for strength (Schaefer & Stewart, 2009).

Genera associated with wood eating:

Panaque in the Hemiancistrus medians group close to genera such as Baryancistrus and Parancistrus (Lujan et al., 2015; Roxo et al., 2019).
Panaqolus was previously in Panaque but identified to be in the Peckoltia group also with genera such as Scobinancistrus and Hypancistrus (Lujan et al., 2015; Roxo et al., 2019).
Hypostomus in the Hypostomus cochliodon group, so not far from Hypostomus plecostomus.
Pseudoqolus, also in the Peckoltia group (Lujan et al., 2015; Roxo et al., 2019).
Potentially Lasiancistrus heteracanthicus, sister genus to Ancistrus (Lujan et al., 2015; Roxo et al., 2019).

These genera have uniquely been identified to also have wood in their stomach (Lujan, German & Winemiller, 2011; German, 2009), aquarists will notice their faeces will also reflect this and, any wood will usually slowly be broken down faster then if there was not these fishes. This doesn’t tell the full picture as many animals including animals consume things that we do not digest, use for digestion or any other purpose.

Questioning their ability to digest wood

The issue is xylovory, the ability to eat wood is quite rare and unseen in fishes so any occurrence would be fascinating to study. In the initial German (2009) experiment neither Panaque nigrolineatus (Royal pleco) hypothesised to be a wood eater and Pterygoplichthys disjunctivus (common pleco) which was used as a detritivore retained any wood in their gut and the fishes actually lost weight throughout German (2009) experiment where the fishes were only provided with wood. In fact the wood passed through their digestive tract in only 4 hours so not nearly enough time to digest wood (German, 2009), in contrast I identified around 2-4 days for Ancistrus on an algivore diet but in Bentley et al. (2026) Planiloricaria took around 4 days for food and even substrate to pass through the gut.

*Panaque cochliodon*, blue eye royal pleco at Maidenhead Aquatics Ascot.

Anatomical issues

Regardless of differences in jaw and tooth shape neither Panaque or Pterygoplichthys actually differed in intestinal anatomy (German, 2009), showing they are unable to digest the wood using an anatomical method. Teeth and jaw shape only allow for so much processing and, even gut anatomy only allows for so much too. In a way the anatomy should just speed up processing, which is why those animals which swallow prey whole have that food in their stomach and then intestines a long time. Wood is particularly difficult to digest due to the lignin and cellulose although this is present in many plants it’s what creates the structure to these plant structures so you’d expect a longer gut should the fish be able to digest wood and in fact it was also shorter for Panaque (German, 2009), I hypothesise this is due to Panaque consuming more microbes, fungi and in some habitats algae (Lujan et al., 2011) opposed to Pterygoplichthys who possibly consumes more algal matter but is also much more of a generalist (Stolbunov et al., 2021) as also consuming plant matter and some invertebrates, perhaps if both feed on algae’s it could infer a difference in algae’s as the vast group differ in structure. Regardless other then jaw anatomy, the wood ‘eating’ species don’t differ.

Are they actually processing any of this wood?

While many studies have identified wood in the guts of these fishes it doesn’t entirely say what is being digested, many organisms consume different items for a variety of reasons and not all are there for a purpose of which I will discuss later. This is where isotopes are useful as these can indicate what food is actually being processed and assimilated. Lujan et al. (2011) used isotopes to identify that of the wood consumed they were not digesting it, instead they were actually digesting the microbes and even the fungi within the wood. This study was the first to not just use Panaque and Panaqolus but additionally used a member of the Hypostomus cochliodon group.

This inability to process wood had additionally been shown in Pterygoplichthys which has never had wood in the gut within Pterygoplichthys disjunctivus (German and Miles, 2010).

Enzymes

German and Bittong (2009) identified that neither Panaque nigrolineatus (Royal pleco) and Pterygoplichthys disjunctivus had nearly enough of the enzymes (cellulase and xylanase) to digest wood.

*Panaqolus albivermis*, Flash/Emperor pleco. Likely female

Gut microbes

This aspect has been debated a little but gut bacteria can significantly influence what we can digest but also what we eat influences the gut bacteria. Neither Panaque nor Pterygoplichthys contained enough gut bacteria that would allow for the digestion of wood when cultured (Nelson et al., 1999); in Panaque nigrolineatus when genetic analyses of gut micromes were assessed (McDonald et al., 2019) or; in a larger study using the DNA and RNA of Panaqolus albomaculatus, Panaqolus gnomus, Panaqolus nocturnus and Panaque bathyphilus (McCauley et al., 2020). When comparing to the wood, those microbes alive in the gut used in digestion also differed but it did leave the opportunity that they are digesting the microbes within natural wood.

Niche Partitioning

All of this evidence (Lujan et al., 2011; McCauley et al., 2020; German, 2009; German and Bittong, 2009; McDonald et al., 2019) proves that there are no xylovorous Loricariids, pseudoxylovory could be a good term but in fact they are detritivores. As earlier the majority of Loricariids are algivores or detritivores (Lujan et al., 2012) which might disappoint a lot of people but this actually says something quite interesting. Loricariids are a massive group of fishes, well over 1,000 species described according to Eschmeyer’s Catalog of Fishes, many are found in the same area. As you might well know, species can’t often co-exist if competing. While these pseudoxylovores (‘wood-eaters’) are not competing due to the use of wood they are actually not competing due to likely where these fishes can find their food, these fishes can find their food in wood, where none of the others actually can. This partitioning of dietary niche is maybe more common in Loricariidae but we don’t really know, there are many algivore’s in the same locality and it’s likely each is eating different algae’s, there is a diversity of jaw and tooth shapes afterall so maybe some are consuming say diatoms and others filamentous algae.

Panaque are actually found in habitats where there isn’t any wood (https://amazonas.dk/index.php/articles/brasilien-rio-xingu), so they are certainly capable of generalisation. Within the aquarium Panaqolus and Hypostomus cochliodon group have proven to be hardy, good growers and long lived and while it is difficult to assume, they might not always be kept around wood. While we like to think of species as specialists, while they are to some extent many also are capable of generalisation, such as why many who are really great at consuming one food item take guinea pigs are great with grass are more then capable at eating a wide range of different plant matter, even if it might not be as good nutritionally to depend on this. This is a massive topic discussed in evolutionary biology for a variety of species.

The reason pleco’s don’t eat wood is why we have so many species available to us. It’s why they are so interesting for evolutionary biology.

*Hypostomus basilisko*, rusty pleco. Member of the *Hypostomus cochliodon* group

Of course this topic actually got wider, like the telephone game people changed their ideas. While no other Loricariid other then these three(ish) genera consume wood, it got extended to a pick and mix of most Loricariids.

So they will eat the microbes within aquarium wood?

This is a common topic brought up, while it is logical we have to remember that we tend to use a very niche range of woods in the aquarium hobby, we also want them to last as long as possible. Microbes within wood are generally there to break down this wood and ideally we, as aquarists want to avoid this so we actively choose woods that last a long time in the aquarium and this means that there will be minimal microbial growth. They obviously just don’t decay quickly enough if lasting years to provide many microbes. We also tend to sterilise the wood beforehand and choose very hard woods, for a variety of reasons aquarium woods are unlikely to have these microbes. McCauley et al. (2020) used similar methods and actually struggled to find microbes involved in wood decay in the gut but also they might not have been able to identify microbes being digested but allowed them to identify any microbes used to digest wood.
Personally, I collect fresh and dried woods of a variety of ‘safe’ trees such as palms, beech, birch, oak and fruit trees, all actually break down quickly sometimes within a year, even before that they become softer and easy to break. So it is clear that most aquarium woods are of not much use, I also personally keep Panaqolus (P. albivermis and P. aff. maccus) and while wood consumption differs they really don’t consume that much. I also find particularly Panaque maybe due to their size prone to stunting when really not fed enough which is common as many do depend on the wood, when I’ve fed them daily or twice daily they do grow much more rapidly.

So they need it for digestion?

This has been mentioned a lot but actually has no backing in science or actually really any reliable origin. I assume it relates to if they cannot digest it, why is it in the gut and many will think about gastroliths, stones within the gut that are used to aid in digestion. While an interesting thought, wood is only found in these few genera, given they are digesting the ‘norm’ compared to the majority of Loricariids (Lujan et al., 2012), why are the others not consuming wood even where wood is present? Many lack the teeth to do so as well, so haven’t evolved the mechanism of consuming even a small amount of wood. There are Loricariids who consume tougher food items from seeds, insects and even molluscs like snails, but many of these have completely different jaw shapes likely aimed at extracting the soft tissues from these items or large pharyngeal jaws. It’s not always well known Loricariids have two pairs of jaws, this means they can actually chew almost twice (Bentley et al., 2026). With the pharyngeal jaws the use of some material to digest makes little sense but also why wood consumption is not so common throughout the group.

*Panaque schaeferi*, royal pleco at Maidenhead Aquatics Ascot.

Consuming items for no purpose

Why is the wood in their gut if it has no purpose? This is likely due to what they are digesting and the niche partitioning, to consume the bacteria, fungi and other microbes they are digesting (Lujan et al., 2011), just to consume these food items with their mouth it is likely to pass through the gut.

One item that doesn’t seem to get discussed is substrate, it is found throughout Loricariid guts (Lujan et al., 2012), so sand is an interesting concept for Loricariids although they definitely have no issue without substrate. So it’s likely again they are consuming a food item because they are foraging around it so it just passes through the gut. This is also observed in Labridae specifically parrotfish which seem to eat sponges but in actual fact they are digesting the microbes within these sponges (Crossman et al., 2005) as identified by Professor Donovan German (https://german.bio.uci.edu/PFK_response.html).

*Panaqolus* aff. *maccus*, one of the clonw pleco’s. Likely female.

Just because it is fed on doesn’t mean it is consumed, other Loricariids.

The issue has become wider though, although originally it was restricted to those pseudoxylophagous species although after the last few years it has spread to a paraphyletic pick and mix of Loricariids. The majority of these species lack the teeth or jaws to consume wood, quite a lot also aren’t found around wood in the wild such as the gold nugget pleco (Baryancistrus xanthellus) who is an extreme algivore almost exclusively found around rocks (Py-Daniel et al., 2011).

This idea is often backed by the idea if the fish are rasping on something or feed on it maybe they are eating it. But this is somewhat flawed, these fishes are evolved to rasp on a surface (Adriaens et al., 2009), it doesn’t mean they eat that surface or find a benefit on rasping from that individual type of surface. Finding some of your food in one place doesn’t mean you depend on this place particularly when algae and detritus grows on a variety of surfaces.

Is there a place for wood?

Ofcourse, it can be a hiding space for many species, it’s also complex in shape so allows for many more different hiding spaces. For those that are considered pseudoxylophagous, while they don’t digest the wood and it’s not used for digestion there is still a behavioural benefit to provide it as it acts as enrichment, it would also be interesting to provide caves made of wood for these species.

So why is this topic an issue?

Initially it seems harmless, wood could provide enrichment benefits so why not provide it? But the harm actually comes from two aspects 1) depending on it as a food source and 2) assuming the lack of it as a cause of death. The first aspect is maybe clearest on Panaque who seem so easily stunted for a generalist, it shouldn’t take 15-20 years for them to reach adult size, particularly when compared to their relatives but with such poor food provision it seems to be the excuse used. The second aspect is more of a feedback issue, when fishes die the assumption the lack of wood is a cause detracts from the actual cause and can mean that that issue is not solved. Loricariids aren’t the super hardy fishes they are often labelled as, they are diverse and complex so we still need to identify issues with water quality, disease, food provision, nutrition etc. blaming the presence of wood solves nothing.

References:

Adriaens, D., Geerinckx, T., Vlassenbroeck, J., Van Hoorebeke, L., & Herrel, A. (2009). Extensive jaw mobility in suckermouth armored catfishes (Loricariidae): a morphological and kinematic analysis of substrate scraping mode of feeding. Physiological and Biochemical Zoology, 82(1), 51-62.

Bentley, R. F., Collins, R. A., & Genner, M. J. (2026). Evolutionary innovation of functional fused molariform pharyngeal jaws in suckermouth catfishes. Evolutionary Journal of the Linnean Society, kzag009.

Crossman, D. J., Choat, J. H., & Clements, K. D. (2005). Nutritional ecology of nominally herbivorous fishes on coral reefs. Marine Ecology Progress Series, 296, 129-142.

German, D. P. (2009). Inside the guts of wood-eating catfishes: can they digest wood?. Journal of Comparative Physiology B, 179(8), 1011-1023.

German, D. P., & Bittong, R. A. (2009). Digestive enzyme activities and gastrointestinal fermentation in wood-eating catfishes. Journal of Comparative Physiology B, 179(8), 1025-1042.

German, D. P., & Miles, R. D. (2010). Stable carbon and nitrogen incorporation in blood and fin tissue of the catfish Pterygoplichthys disjunctivus (Siluriformes, Loricariidae). Environmental Biology of Fishes, 89(2), 117-133.

Lujan, N. K., Armbruster, J. W., Lovejoy, N. R., & López-Fernández, H. (2015). Multilocus molecular phylogeny of the suckermouth armored catfishes (Siluriformes: Loricariidae) with a focus on subfamily Hypostominae. Molecular phylogenetics and evolution, 82, 269-288.

Lujan, N. K., German, D. P., & Winemiller, K. O. (2011). Do wood‐grazing fishes partition their niche?: morphological and isotopic evidence for trophic segregation in Neotropical Loricariidae. Functional Ecology, 25(6), 1327-1338.

McCauley, M., German, D. P., Lujan, N. K., & Jackson, C. R. (2020). Gut microbiomes of sympatric Amazonian wood‐eating catfishes (Loricariidae) reflect host identity and little role in wood digestion. Ecology and Evolution, 10(14), 7117-7128.

Nelson, J. A., Wubah, D. A., Whitmer, M. E., Johnson, E. A., & Stewart, D. J. (1999). Wood‐eating catfishes of the genus Panaque: gut microflora and cellulolytic enzyme activities. Journal of fish biology, 54(5), 1069-1082.

Py-Daniel, L. R., Zuanon, J., & Oliveira, R. R. D. (2011). Two new ornamental loricariid catfishes of Baryancistrus from rio Xingu drainage (Siluriformes: Hypostominae). Neotropical Ichthyology, 9(2), 241-252.

Roxo, F. F., Ochoa, L. E., Sabaj, M. H., Lujan, N. K., Covain, R., Silva, G. S., … & Oliveira, C. (2019). Phylogenomic reappraisal of the Neotropical catfish family Loricariidae (Teleostei: Siluriformes) using ultraconserved elements. Molecular phylogenetics and evolution, 135, 148-165.

Schaefer, S. A., & Stewart, D. J. (1993). Systematics of the Panaque dentex species group (Siluriformes: Loricariidae), wood-eating armored catfishes from tropical South America. Ichthyological Exploration of Freshwaters, 4(4), 309-342.

Stolbunov, I. A., Gusakov, V. A., Dien, T. D., & Thanh, N. T. H. (2021). Food spectrum, trophic and length-weight characteristics of nonindigenous suckermouth armored catfishes Pterygoplichthys spp.(Loricariidae) in Vietnam. Inland Water Biology, 14(5), 597-605.

Pleco Teeth, what snails can teach us about Loricariids.

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While it is not always obvious Loricariids all have teeth and they show a wide range of morphological disparity (Lujan & Armbruster, 2012). Morphological disparity refers to that range of different anatomy within a group. Unlike many fishes Loricariids are rarely gape limited, their prey (that includes algae) is not limited by the size of their mouth and this makes comparison with traditional fishes like carp or cichlids limited.

Figure 1: Pterygoplichthys joselimaianus jaw, a typical jaw for Loricariidae.

Loricariids feed largely by a rasping motion, this is extremely similar to how snails feed. Snails also have teeth on a ribbon like organ known as a radula (Fig 2).

Figure 2: Snail body plan including the mouth anatomy. Unknown source.

Both snails and Loricariids use their jaws, containing the teeth to basically scrape at a surface (rasp), it can be the food item itself but it could be rocks or wood to extract food.

While I say the majority of Loricariid jaws are similar to snails not all are, there are carnivorous genera such as Pseudohemiodon or Scobinancistrus who differ in how they move and function. Carnivorous genera have elongate fewer teeth with often narrower oral jaws but can be much more robust (Fig 3), or in some those oral jaws are almost entirely just the jaws, reduced tooth cups. It’s easy to say these carnivores are using different morphology for the same solution to carnivory but maybe in a different place, one feeds amongst crevices (those with the elongate teeth and jaws) and others amongst the substrate (those with reduced jaws). We do have a slight exception with Spatuloricaria, an obvious substrate feeder but it seems to use the substrate a little differently and feed on different invertebrates.

Figure 4: Gastropod radula diversity. Krings, W., Kovalev, A., & Gorb, S. N. (2021). Collective effect of damage prevention in taenioglossan radular teeth is related to the ecological niche in Paludomidae (Gastropoda: Cerithioidea). *Acta Biomaterialia*, *135*, 458-472.

Snails, Gastropods have long been studied in terms of their radula diversity (Fig 4), I assume this is due to the fact when you’re dealing with preserved snails there are fewer tissues to identify the species. Additionally they make great models for understanding how anatomy relates to morphology, ecomorphology. Gastropods are everywhere and it’s easy to find those that scrape algae’s off rocks vs more carnivorous gastropods. To put it simply though, Gastropods feed by rasping and their teeth are uniquely shaped to what they are feeding on.

I think even just ignoring carnivory Loricariidae shows a wide diversity of tooth morphological disparity but there is little studies regarding that in relation to their ecology. Plenty of these studies focus on the development and morphology (Geerinckx et al., 2007). What there is is a fascinating study looking at another part of the fishes anatomy that could be similar, the unculi, small protrusions on the oral disc’s of the fishes. While the study focuses on how these structures allow for the fishes to inhabit certain habitats, could these also function in a similar fashion to radula?

Figure 5: The diversity of Loricariid teeth, Geerinckx, T., De Poorter, J., & Adriaens, D. (2007). Morphology and development of teeth and epidermal brushes in loricariid catfishes. *Journal of morphology*, *268*(9), 805-814.

The diversity of Loricariid tooth morphological diversity is clear (Geerinckx et al., 2007) and we clearly see that Loricariids have a diversity of diets beyond herbivory and carnivory (Lujan et al., 2012), whatever they really mean to aquatic animals.

When looking outside of carnivory there is clear differences in morphology, none are so much clearer then those Loricariids that utilize wood. These genera display clearly spoon shaped teeth even if these genera (Panaqolus, Panaque, Hypostomus cochliodon group etc.) do not digest the wood and it is simply where they might find food. Compared with carnivores such as Leporacanthicus, these have more elongate teeth but it depends on where they are accessing their food. This difference is also reflected in gastropods whether they be snails or slugs have evolved teeth on their radula that reflect not just their diet but the methods they use to extract it. Elongate pointed teeth infers carnivory whereas further cusps leans towards herbivory. Perhaps carnivory requires less complexity to herbivory and I assume largely as carnivory relies on more then the teeth to extract food.

References:

Geerinckx, T., De Poorter, J., & Adriaens, D. (2007). Morphology and development of teeth and epidermal brushes in loricariid catfishes. Journal of morphology, 268(9), 805-814.

Krings, W., Konn-Vetterlein, D., Hausdorf, B., & Gorb, S. N. (2023). Holding in the stream: convergent evolution of suckermouth structures in Loricariidae (Siluriformes). Frontiers in Zoology, 20(1), 37.

Krings, W., Kovalev, A., & Gorb, S. N. (2021). Collective effect of damage prevention in taenioglossan radular teeth is related to the ecological niche in Paludomidae (Gastropoda: Cerithioidea). Acta Biomaterialia, 135, 458-472.

Lujan, N. K., & Armbruster, J. W. (2012). Morphological and functional diversity of the mandible in suckermouth armored catfishes (Siluriformes: Loricariidae). Journal of Morphology, 273(1), 24-39.

Pleco’s and Whiptail Catfishes, the Beginners Guide to Loricariid catfishes.

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With a whole section designated to Loricariidae, I haven’t actually done a beginners guide to the group. This website largely isn’t designed for beginners but Loricariid’s are some of the most misunderstood group of fishes.

What is a Pleco or Whiptail Catfish?

These two common names have no certain definitions, the majority of their use is a pick and mix that varies between the user. It is even more confusing that some loaches are referred to as pleco’s. All common names are equally as valid as each other. I find it easier to refer to the whole of Loricariidae as plecos, why? Figure 1 explains this situation. By excluding the subfamily Loricariinae (whiptail catfishes), you exclude Loricariichthys of which Plecostomus was synonymized with. If you exclude Hypoptopominae (Otocinclus and relatives) then Neoplecostomini and Neoplecostomus are excluded. Ancistrus, commonly known as bristlenose’s places right in the middle of Hypostominae, traditional plecos but Ancistrus also includes the medusa pleco, Ancistrus ranunculus. Then outside of all of these groups is Rhinelepinae, so that includes the pineapple pleco’s, and on it’s own Pseudancistrus genisetiger, so none of those are plecos then?

What would solve the common name issue? Simply not using them. Sadly with Loricariids you can’t avoid scientific names as many species do lack common names or share them.

Figure 1: Annotated phylogeny of Loricariidae from Roxo, F. F., Ochoa, L. E., Sabaj, M. H., Lujan, N. K., Covain, R., Silva, G. S., … & Oliveira, C. (2019). Phylogenomic reappraisal of the Neotropical catfish family Loricariidae (Teleostei: Siluriformes) using ultraconserved elements. *Molecular phylogenetics and evolution*, *135*, 148-165.

What is the L number system?

The L number system is actually quite simple, it is a hobby made system originating from the German Magazine, DATZ. It simply designates an L number to a variant or species. It is commonly stated that undescribed species are given L numbers, this is partially true but there are many species who were described decades or over 100 years before given their L number such as the sailfin/common/leopard pleco, Pterygoplichthys gibbiceps who was described by Kner in 1854.

I am not entirely convinced the L number system is easy to use, the order of the numbers doesn’t infer anything regarding the fishes care or lineages. Multiple species can share an L number e.g. Baryancistrus demantoides and Hemiancistrus subvirdis are both L200 also known as green phantoms. Hemiancistrus subvirdis is likely the same species as L128 although that is a topic for another day. One species can have multiple L numbers, which don’t always describe populations or all of the morphological variation of the species e.g. Baryancistrus xanthellus has 4 L numbers.

To top it off there are fake L numbers, L600 for example described Pseudacanthicus leopardus who already has the L numbers, L114 and L427. The L number system is only up to around 530 species so far. The letters added to L numbers aren’t a part of the L number system and increase confusion. Sometimes species are given by the hobby the L number of an entirely different species such as L144 which doesn’t even exist in the hobby and hasn’t done for decades or L056 for Parancistrus aurantiacus when actually that L number refers to an undescribed brown Pseudancistrus.

There is additionally the LDA number system which does overlap slightly but isn’t so expansive.

Introduction

Loricariidae, pleco’s are the largest family within the order of fishes known as Siluriforme also known as catfishes or welse, representing 1050 currently described species (Fricke et al., 2024). This group is exclusive to South and Central American freshwaters although has invasive populations in many continents.

*Panaque nirolineatus* from Maidenhead Aquatics at Ascot.

The family is identified by a downwards (ventrally) facing oral disc shaped mouth, in some species this is more of a suction cup whereas others they cannot attach to surfaces well or at all. This trait isn’t exclusive to Loricariids but it is not quite the same in other groups. Further more, Loricariids are defined by having a body covered in bony scutes, more scientifically known as dermal plating, not scales as catfishes lack scales.

Not does Loricariidae just have dermal plating but they have spines known as odontodes, external teeth (Fig 2). Sometimes these are sexually dimorphic but not always, they can also be shed seasonally.

Figure 2: Odontodes found on I believe *Peckoltia sabaji*.

Loricariids realistically are one of the most morphologically diverse clades of fishes.

This diversity means that as a group, Loricariids are really difficult if impossible to generalize, research is paramount for this group.

The size of plecos

As one of the most diverse groups of fishes their size varies vastly, 0.2-0.8cm in Parotocinclus halbothi (Lehmann et al., 2014) to 100cm SL possibly in Acanthicus adonis. There is a wide diversity of sizes within many groups so there is no shortage of smaller and larger species. At the end of the article I will recommend reliable websites, there is frequent misleading information about the adult size of many species.

It is important to recognize reliable websites will use standard length, from the head to the base of the caudal/tail fin. That caudal/tail fin will be excluded as these can vary in length. I mention this as many people will not consider this measurement and forget their fish grows much bigger then they would originally consider. This is explained in detail in this article.

What should I feed my pleco?

This topic has the majority of misconceptions about Loricariids, the majority are algivores or detritivores (Lujan et al., 2012) but a wide range of diets are utilized. I have written a range of articles on a wide variety of diets across the family: Hypancistrus (zebra, king tigers, queen arabesque, snowball pleco, L236 etc.), Panaque and Panaqolus (royal pleco’s, flash pleco and the clown pleco’s), substrate dwelling Loricariinae (Pseudohemiodon, Planiloricaria etc.), Baryancistrus (gold nugget pleco, mango/magnum pleco, snowball pleco), mollusc specialists (Scobinancistrus, goldie/sunshine pleco, vampire pleco, galaxy pleco, Leporacanthicus), Chaetostoma (Rubbernoses and one of the bulldog plecos) and finally algivores/detritivores.

There are a few myths regarding Loricariid diets I will summerise:

Pleco’s are largely carnivores, there are plenty of papers discussing their diets and while I wont cite them all Lujan et al. (2015) summerises it well.
Pleco’s become carnivorous with age, there isn’t any studies regarding change in diet as the fishes age. Unlike most fishes, the majority of Loricariids break down their food before it enters their mouth, so the size of the fish doesn’t limit their food item, so not gape limited. This means unlike many other fishes their food item doesn’t need to change with size.
Pleco’s clean a tank, while the majority are algivores and detritivores (Lujan et al., 2015) there is a wide diversity in niche partitioning (Lujan et al., 2011) and therefore those algivore’s specialize in certain algae’s. These algae’s seem not to be those that are an issue in the aquarium. Given their lifespan and waste production, they could be an expensive solution to high nutrients.
Pleco’s don’t eat cyanobacteria, they actually don’t just eat those that are pests in the aquarium, in the wild they feed on cyanobacteria (Valencia & Zamudio ,2007).

Always check the ingredients as some diets that claim to contain algae’s might contain anything from none to 5%.

Do pleco’s need wood?

This is discussed in more detail here: Panaque and Panaqolus (royal pleco’s, flash pleco and the clown pleco’s).

In simple NO, they do not need wood. The only species that utilize wood are in the genera Panaque, Panaqolus, Hypostomus cochliodon group, Pseudoqolus and perhaps Lasiancistrus heteracanthicus. These groups all share unique spoon shaped teeth they can gouge into wood and if found among wood, wood is found in their gut (Lujan et al., 2017). No other Loricariid has wood in their gut, I’ve scoured gut records but they simply don’t have the jaws or teeth to gouge into wood. There have been many studies to confirm these fishes do not eat/digest the wood (Watts et al., 2021; German, 2009), instead they are just evolved to feed on biofilms, like other species from where other species cannot access, within wood (Lujan et al., 2011).

What parameters do pleco’s need?

While the general idea is that Loricariids and in general anything South America requires soft, low conductivity and acidic water there is a wide diversity of parameters. Some species are found in lower temperatures while other much higher, 28c or higher (Collins et al., 2015; Urbano‐Bonilla & Ballen et al., 2021). Other misconceptions are that South American habitats have a lot of leaf litter and is black water, this is completely untrue, there are many different habitat types (Bogotá-Gregory et al., 2020). In general the majority of Loricariidae are rheophilic and would benefit from a current within the aquarium although there is some diversity (Krings et al., 2023). In general any current within the aquarium is a lot weaker then any of the weaker streams in their wild range.

Planet Catfish has really accessible information to identify parameters before looking into the scientific literature.

What decor do plecos require?

This is largely the only consistent aspect of Loricariids. If anyone has kept Loricariids they will know how much they like cracks, crevices, hiding spaces, rocks, branches and in general cover. There are many caves and tunnels on the market designed for the preferences of a variety of species. I recommend stacking up wood or rocks in a careful way so nothing falls but this will create many more caves.

Tankmates

This will always be based on experience and understanding of the fishes. It’s important to recognize a few key things about Loricariids.

Loricariids do not often feed rapidly but even if they do it can take them minutes to an hour to reach food. Fast feeding fishes such as most cichlids, loaches, tetra, livebearers and goldfish particularly in large numbers are a bad idea.
Their temperature might not overlap.
They will need a current, some more then others which this means they wont work with fishes like long finned Betta splendens.
While some Loricariids feed on food items that they wouldn’t naturally it doesn’t mean it is good for them. Bloat can happen in some genera more then others. So I do not recommend keeping other fishes with Loricariids who you plan on feeding anything like beefheart.
Hardness, conductivity etc. We don’t actually know the KH or GH of the water many of these fishes come from, usually we have conductivity and pH records for many waters. Ideally these fishes are ill-suited regardless with Rift Valley cichlids, generally the biggest issue is above, those cichlids feed way too rapidly for any Loricariid.

Recommended websites

Planet Catfish

Scotcat

Loricariidae.info

L-Welse

www.suedamerikafans.de

References:

Collins, R. A., Ribeiro, E. D., Machado, V. N., Hrbek, T., & Farias, I. P. (2015). A preliminary inventory of the catfishes of the lower Rio Nhamundá, Brazil (Ostariophysi, Siluriformes). Biodiversity Data Journal, (3).

Bogotá-Gregory, J. D., Lima, F. C., Correa, S. B., Silva-Oliveira, C., Jenkins, D. G., Ribeiro, F. R., … & Crampton, W. G. (2020). Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages. Scientific Reports, 10(1), 15349.

Fricke, R., Eschmeyer, W. N. & Van der Laan, R. 2024. ESCHMEYER’S CATALOG OF FISHES: GENERA, SPECIES, REFERENCES. (http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp). Electronic version accessed 22 July 2024.

German, D. P. (2009). Inside the guts of wood-eating catfishes: can they digest wood?. Journal of Comparative Physiology B, 179, 1011-1023.

Lehmann, P. A., Lazzarotto, H., & Reis, R. E. (2014). Parotocinclus halbothi, a new species of small armored catfish (Loricariidae: Hypoptopomatinae), from the Trombetas and Marowijne River basins, in Brazil and Suriname. Neotropical Ichthyology, 12, 27-33.

Lujan, N. K., Cramer, C. A., Covain, R., Fisch-Muller, S., & López-Fernández, H. (2017). Multilocus molecular phylogeny of the ornamental wood-eating catfishes (Siluriformes, Loricariidae, Panaqolus and Panaque) reveals undescribed diversity and parapatric clades. Molecular phylogenetics and evolution, 109, 321-336.

Lujan, N. K., Winemiller, K. O., & Armbruster, J. W. (2012). Trophic diversity in the evolution and community assembly of loricariid catfishes. BMC Evolutionary Biology, 12, 1-13.

Urbano‐Bonilla, A., & Ballen, G. A. (2021). A new species of Chaetostoma (Siluriformes: Loricariidae) from the Orinoco basin with comments on Amazonian species of the genus in Colombia. Journal of Fish Biology, 98(4), 1091-1104.

Valencia, César Román, and Héctor Zamudio. 2007. Dieta y reproducción de Lasiancistrus caucanus (Pisces: Loricariidae) en la cuenca del río La Vieja, Alto Cauca, Colombia. Revista del Museo Argentino de Ciencias Naturales nueva serie 9(2): 95-101.

Watts, J. E., McDonald, R. C., & Schreier, H. J. (2021). Wood degradation by Panaque nigrolineatus, a neotropical catfish: diversity and activity of gastrointestinal tract lignocellulolytic and nitrogen fixing communities. In Advances in Botanical Research (Vol. 99, pp. 209-238). Academic Press.

The Myth of Female Aggression: A Focus on Territoriality in Loricariids (Pleco’s) Catfishes.

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Men are from Mars and Women are from Venus, Mars the roman god of war and Venus the Roman goddess of love and fertility. Males of a species are often associated with aggression and self determination; females associated with passivity and a peaceful nature. Species such as the Spotted Hyena (Crocuta crocuta) that so obviously turn this view upside down are often of curiosity.

Misconceptions of female aggression are common throughout all vertebrates for various reasons. Within horses one mare determines where the rest of the group are going and the others can determine if to tolerate the male or not. They show a range of different aggressive behaviours between each other and towards males (Curry et al., 2007), hierarchy is as important in the females in a group as it is for males. It’s not all about reproduction but social positioning can effect a females chance as it does for males.

Cichlid Aggression

Cichlids are well known for aggression, perhaps it is a bit overemphasized as their behaviour is much more complex then just needless aggression. It is also a vast grouping where levels of aggression and territoriality vary along with the reasons for. And like Loricariids there are social species and more solitary species, juveniles of any will spend a considerable amount of time in a gregarious state (Forsatkar et al., 2016).

Territoriality is common in cichlids where both males and females defend a space particularly if spawning. In species with large size disparity the females contribution might be easily forgotten yet keep a female alone regardless of the presence of eggs and it is notable she is not a passive individual. In hareming species such as many Apistogramma or the shelldwelling Neolamprologous males hold a larger territory. The females are not shoaling passively, they each hold their own territory within the males defending from other females and sometimes keeping the male within a reasonable distance should there be fry and eggs. Interestingly males play a role in mediating aggression between females (Walter & Trillmich, 1994), this is a role I have seen in other animals where the mixture of sexes reduces overall aggression.

The Siamese Fighting Fish, Betta splendens

This species has been the objects of fascination for many for the males beautiful morphology and their territorial behaviour. While the males have often been the highly valued fishes, females are seen as a side addition. Neither sex is social in the wild, these are largely solitary, territorial fishes so the benefit of keeping females in a group is only that of the owners. Females are shown to be equally as aggressive as males with similar aggressive behaviours (Braddock & Braddock, 1955). Where females are not known for aggression likely stems from the majority of these being plakat, short finned whereas many males are long finned and therefore will struggle with any territorial interactions.

Although it could be argued in a sufficiently big enough tank multiple individuals of both sexes could provide social enrichment assuming they can all develop their own territory. I would largely only advice keeping individuals alone unless spawning, there are social species of Betta that might be a better option for some.

I have worked with and kept a lot of Betta splendens, they are a staple of the aquarium trade and if anything can be a problem is sorority setups. Due to the amount of tanks needed to store individuals only males and the most fancy females could be housed alone. In these sorority tanks there was always a high rate of injuries between individuals, some variants were worse then others, particularly long finned females. In store setups it’s quite easy to experiment and increasing the amount of decor or adding in a variety of different tankmates did not reduce these aggressive interactions.

Why might females display aggression?

Sociality, even a gregarious species will have many complex interactions between individuals. Maintaining ones place within a shoal hierarchy is a common cause for aggression.
Territoriality, maintaining a space in which might contain resources such as food or the best spawning caves. Aggression to defend an item of food is common because this will aid in them maintaining a good condition.
Reproduction, sometimes females will defend the offspring from other species, individuals or even the male.

Loricariid (pleco) aggression

Loricariidae is a 1,051 species strong family of fishes so they cannot easily be generalised. There are both gregarious and territorial species within this gigantic clade. Generally Hypoptopominae are social and gregarious, Rinelepinae I have not heard of aggression from this strange subfamily. Deluturinae and Lithogeninae are subfamilies which never reach the aquarium trade so easily can be ignored here. This leaves the two largest subfamilies, Loricariinae and Hypostominae.

Loricariinae (Whiptail catfishes), the majority of these are social such as Farlowella (twig catfish), Sturisomatichthys (royal whiptail), even those which are not the steryotypical pleco/Loricariid like Rineloricariae. Although some species like Planiloricaria cryptodon can be particularly aggressive, it’s not entirely clear why, these are a species that spawns using their amazing barbels so not need to defend a spot. It is not sex specific but in caring for them around maturity they really need a larger tank or one per a tank.

Hypostominae, the largest subfamily with over 500 species. The majority of fishkeepers keep juvenile and with their illusive behaviour many interactions are easily missed. There is only a small number of gregarious species in this subfamily who lack any territorial tendencies e.g. Ancistrus ranunculus. Hypostominae are far from peaceful in general, sometimes fearsely defending an area from congeners (Hossain et al., 2018).

*Hemiancistrus subvirdis* (Green Phantom Pleco, L200) at Acres Aquatics, Wiltshire.

Hypostominae are crevice spawners in which a male defends a cave when there are fry or eggs within the space (Secutti, S., & Trajano, 2009). Although this doesn’t mean females do not express any aggression, both are territorial and will defend their space from any similarly shaped and sized fishes. It’s not difficult to understand why, as these fishes are likely defending food resources and the best caves to hide from predators regardless if used for spawning. The best grazing spots for many species are probably quite highly prized. Females are only spawning for short periods of time as play no role in brood care (Mendes et al., 2018), but as a result unlike males they tend to roam much larger areas, regarding aggression this poses a larger issue to the fishkeeper.

Some genera display much higher levels of aggression then others, the Acanthicus clade is particularly noted for aggression even in juveniles Pseudacanthicus will rasp on each other. Hypostominae are not loyal with their pairs although fishkeepers have noted aggression towards other fishes of both individuals in a pair preventing other fishes being added. I myself have quite a few mature Baryancistrus, in which the females I’ve seen lunge at other fishes, ram others into caves and intense shoving matches. In the common bristlenose, an Ancistrus, two mature females where this shoving match resulted in serious injuries. I have worked with an adult female Hypostomus luteus who couldn’t be housed with any other fishes within the restricted space of an aquarium after chasing many Pterygoplichthys non-stop.

Juvenile *Pseudacanthicus serratus* (Black mustang pleco)

Aggression is not restricted to males and for many species they are not easy to sex so for the majority of fishkeepers they would not know whether this fish is male or female. They are fishes who enjoy having their own space so plenty of caves and the space needed, it doesn’t mean multiple species can’t be kept together it just means consideration is needed. Aggression is also not limited to being intrasexual as individuals of different sexes will also display aggressive behaviours when not spawning.

The issue with Loricariidae is outside their phylogenetics and taxonomy we don’t know an awful lot about them so there is little research into their behaviour and the causes of territoriality between the two sexes.

Conclusion

Aggression is found throughout many clades of fishes and there are many different triggers for this behaviour. Where a male is aggressive it’s likely the females will be too and sometimes much more then those males.

References:

Braddock, J. C., & Braddock, Z. I. (1955). Aggressive behavior among females of the Siamese fighting fish, Betta splendens. Physiological Zoology, 28(2), 152-172.

Curry, M. R., Eady, P. E., & Mills, D. S. (2007). Reflections on mare behavior: Social and sexual perspectives. Journal of veterinary behavior, 2(5), 149-157.

Forsatkar, M. N., Nematollahi, M. A., & Bisazza, A. (2016). Quantity discrimination in parental fish: female convict cichlid discriminate fry shoals of different sizes. Animal cognition, 19, 959-964.

Hossain, M. Y., Vadas Jr, R. L., Ruiz-Carus, R., & Galib, S. M. (2018). Amazon sailfin catfish Pterygoplichthys pardalis (Loricariidae) in Bangladesh: a critical review of its invasive threat to native and endemic aquatic species. Fishes, 3(1), 14.

Mendes, Y. A., Lee, J. T., Viana, I. K., Rocha, R. M., & Ferreira, M. A. (2018). Reproductive biology of the tiger pleco Panaqolus tankei (Loricariidae) in a lentic system of the Amazon Basin. Journal of Fish Biology, 93(4), 711-714.

Secutti, S., & Trajano, E. (2009). Reproductive behavior, development and eye regression in the cave armored catfish, Ancistrus cryptophthalmus Reis, 1987 (Siluriformes: Loricariidae), breed in laboratory. Neotropical Ichthyology, 7, 479-490.

Walter, B., & Trillmich, F. (1994). Female aggression and male peace-keeping in a cichlid fish harem: conflict between and within the sexes in Lamprologus ocellatus. Behavioral Ecology and Sociobiology, 34, 105-112.

What is a pleco? To be a pleco or not to be a pleco

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Common names are half a mystery to themselves, their origins and what species they really apply to and not. They lack regulations and frequently change spatially and temporally. You can’t expect to go to every country and people call a giraffe, Giraffa, a giraffe. It’s like you can’t expect common names to stay the same, a well known example would be the European robin, Erithacus rubecula was at one point called the redbreast and then that changed to robin redbreast and then just robin. The point maybe is common names change so much with little ability to track, plant common names do so frequently as well.

Pleco is one of those common names, originally Plecostomus but Plecostomus used to be the name of a genus. Much like many have created Cory as a common name for the genus Corydoras. The type and most notable species was Hypostomus Plecostomus (Linnaeus 1758), formally Plecostomus Plecostomus. Plecostomus is no longer a valid genus and has not been since 1980 where species were then placed in multiple other genera such as Ancistrus, Isorineloricaria, Loricariichthys and eventually Aphanotorulus. The majority of those previously known as Plecostomus were moved into Hypostomus, described in 1803 with the type Hypostomus guacari which is now understood to be a synonym of Hypostomus plecostomus (Fricke et al., 2023). Interestingly Pterygoplichthys, a genus that contains species known as the common plecos was never in the genus Plecostomus. This summarizing the main flaws of the arguments behind the common name. Ancistrus, bristlenose plecos are often argued not to be plecos but they had members once in Plecostomus whereas many such as Pterygoplichthys who there is no debate about were never placed in Plecostomus. Currently while there are none with the genus Plecostomus there is Hypostomus plecostomus and H. plecostomoides. Of genera Neoplecostomus, Microplecostomus and Nannoplecostomus exists, currently within Hypoptopominae, which is the same subfamily as Otocinclus. These genera add the other argument do people consider Otocinclus a pleco?

The other issue with the name pleco as a common name is where it is applied evolutionary.

Phylogenetic tree using molecular data of Loricariidae from: Roxo, F. F., Ochoa, L. E., Sabaj, M. H., Lujan, N. K., Covain, R., Silva, G. S., … & Oliveira, C. (2019). Phylogenomic reappraisal of the Neotropical catfish family Loricariidae (Teleostei: Siluriformes) using ultraconserved elements. *Molecular phylogenetics and evolution*, *135*, 148-165.

Names need some consistency so people can understand each other and that is what scientific names provide. The common name pleco also lacks consistency in where it places in the evolutionary/phylogenetic tree. If you exclude Ancistrus as so many do it is the only member of Hypostominae (coloured in red, Fig 1) to not be a pleco. But members outside of that subfamily are included, right at the earliest branches is Rinelepinae (coloured in yellow, Fig 1) it excludes a lot of later branching Loricariids. Not pictured here is also Pseudancistrus geniseiger who would be considered a pleco and also branches out this far (Lujan et al., 2015). Loricariinae and Hypoptopominae are often debated as if they are a pleco or not.

The problem is more that no one is quite referring to pleco in the same way under this pick and mix system. Some of us refer to the whole of Loricariidae as it would make sense to do, L numbers themselves also do as the L refers to Loricariidae. In Germany these fishes are often referred to as L Welse, meaning Loricariidae Catfish I assume as also members of Siluriforme, catfishes. It means everyone understands each other using this method even if being much broader, we should be recognising the diversity within Loricariidae anyway. In Loricariids and therefore plecos it is an international aspect of the fishkeeping hobby and many countries do not even use the term pleco.

References:

Britto, M. R. (2003). Phylogeny of the subfamily Corydoradinae Hoedeman, 1952 (Siluriformes: Callichthyidae), with a definition of its genera. Proceedings of the Academy of Natural Sciences of Philadelphia, 153(1), 119-154.

Fricke, R., Eschmeyer, W. N. & Van der Laan, R. (2023). ESCHMEYER’S CATALOG OF FISHES: GENERA, SPECIES, REFERENCES. (http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp). Electronic version accessed 18/10/2023.