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This is a big question when it comes to keeping Loricariids in the aquarium as more then often people want to spawn the fishes but sometimes people just want to name them.

What is the sex determination methods in Loricariidae?

This is actually a more vast discussion then some other groups like mammals. In fact Loricariid’s use a range of karyotypes to determine sex from the more well known ZW and XY to multiple sex chromosomes. Ancistrus (Bristlenoses) is a large genus representing over 60 spp. (Eschmeyer, 2025), this genus does show multiple sex determination methods and some not as well known such as ZZ/ZW₁W₂ in Ancistrus clementinae (Nirchio et al., 2023) or ZZ/ZW in Ancistrus ranunculus (Oliveira et al., 2007). It seems many genera show a lot of diversity (Sassi et al., 2023) and this is possibly a large barrier to hybridization and maybe could lead to speciation.

What do you need to be able to identify the sex of your Loricariid?

A mature fish, unless the fish has reached sexual maturity it likely wont show many sexually dimorphic features although there are slight exceptions at the smaller level or during dissection. Largely this will mean close to fully grown and/or clearer odontode growth. Some species this might take a year such as some of the more common Ancistrus or 5+ years like the Hemiancistrus medians group (e.g. Panaque, Baryancistrus etc.)
A bowl, container or polybox can be useful to examine around the fish particularly below. Fill this with the tank water, do not do it during acclimation. It can be done in store.

Anatomy that allows you to sex Loricariids

Venting – Genital papilla and the urogenital pore

Figure 1: *Baryancistrus chrysolomus*, mango/magnum pleco juvenile.

The genital papilla and the urogenital pore are the same thing, this is a combined organ where the fish passes waste but also the gametes (eggs and sperm). This is not the same for all Loricariids where the genital pore is separate from the anus such as in Neoplecostomus. It is clearly on the abdomen, shape is normally ambiguous in juveniles.

The shape of the genital papilla is the most reliable method to sex Lorcariids, it’s most easily stated as V shaped in males and U in females. This can be tricky to see in some genera which have more elongate genital papilla such as the Pterygoplichthys in figure 2.

Figure 2: created by In the Bag Tropical Fish UK, Alice Cook. Depicting *Pterygoplichthys pardalis* and *Pterygoplichthys gibbiceps*.

Figure 4: Mature female Baryancistrus chrysolomus, not showing the clearest maturity.

Some other genera the females are much wider so it is much more square as above. The best method is to see multiple individuals and compare between them which can be done against the glass and taking photos or even within a container to take a more up close look.

Figure 5: The genital papilla of Chaetostoma as explained by Lujan et al. (2015) in Lujan, N. K., Meza-Vargas, V., Astudillo-Clavijo, V., Barriga-Salazar, R., & López-Fernández, H. (2015). A multilocus molecular phylogeny for Chaetostoma clade genera and species with a review of Chaetostoma (Siluriformes: Loricariidae) from the Central Andes. *Copeia*, *103*(3), 664-701.

I find this method the most reliable particularly as there is less individual variation between individuals and also depends less on the age of the fish. The shape can be applied also to Loricariinae (whiptail catfishes) and Hypoptopominae (Otocinclus, Parotocinclus, Hypoptopoma etc.).

The final part of the genital papilla when it comes to sexing Loricariids is spotting around this region in females. These papilla/spots can be green or yellow in colour and can range from one to many in number, once visible to the eye it hints maturity in the females. While it is very obvious in Hypostominae (traditional pleco’s) it is unclear as to if these are present in the other subfamilies even the distantly related but similarly looking Pseudancistrus genisetiger (slate pleco’s) and Rhinelepinae. Although I have been told by Fauna Tropica (https://www.faunatropica.eu/) that these spots can be seen under a microscope and maybe a macrolens before maturity even as younger juveniles.

Figure 6: Genital papilla of a female Baryancistrus chrysolomus.

Body shape

I am not a massive fan of using body shape as it can depend on many factors. Using how plump the fish is does depend on how well the fish has been fed but also females once the female has released eggs can suddenly reduce weight.

Head shape does seem the most reliable method regarding the general anatomy but can be limited when it comes to stunted fish but there is also a lot of individual variation. In general it is assumed females display more elongate heads whereas males are shorter and wider, this is a trend we do see in other fishes.

Figure 7: Body shape in two different Scobinancistrus species but clearly shows the sexual dimorphism.

Personally when it comes to sexing individuals from photos I am less of a fan of this method as it does rely even more on angle of the photo but also maturity. You can see a larger difference in some genera then others and some species you might not see it at all.

Odontodes

Odontodes are the external teeth that cover Loricariids, this does include everything from Otocinclus to Farlowella to Hypancistrus. In some species they can be enlarged in certain areas and this is known as hypertrophied, further in some these odontodes can be sexually dimorphic. Odontodes as a secondary sexual characteristic though are not a rule and there are many exceptions, in addition they can be seasonal so males might have reduced ones seasonally and females can have larger ones, it depends on the genus.

Figure 9: *Panaqolus albivermis* (flash pleco), male showing clear hypertrophied odontodes.

Odontodes are most useful in the Peckoltia clade, this includes Hypancistrus, Peckoltia, Panaqolus, Pseudoqolus, Ancistomus and Scobinancistrus. Although Scobinancistrus and species such as Peckoltia sabaji do not have particularly sexually dimorphic odontodes and I recommend using the genital papilla. These odontodes are hypertrophied in all individuals at the gill opercular although can be larger in males. The most obvious method with this clade is hypertrophied odontodes on the caudal peduncle and pectoral fin of the males.

Figure 10: *Baryancistrus demantoides* (high finned green phantom), female.

When using this trait be careful with other clades, some such as the Hemiancistrus medians group which includes Hemiancistrus medians, some other Hemiancistrus (this genus requires revision), Panaque, Parancistrus, Baryancistrus and some Spectracanthicus (again another genus that requires revision). In these clades I find females can grow large odontodes seasonally and this was very evident to me in a clearly female Baryancistrus demantoides (Fig 10). The key thing to note about odontodes is they can be shed.

Figure 11: *Farlowella vittata* group pictured at Aqualife, Leyland.

Another clade that easily gets forgotten is Loricariinae, while genital papilla are a clear way to sex many genera within this subfamily. Odontodes can provide an additional quick way to sex many particularly Farlowellini (Farlowella, Sturisoma and Sturisomatichthys mostly; Fig 11). These are reliably hypertrophied around the head and/or rostrum in this clade.

Tentacles

This is an exclusive trait to the genus Ancistrus and the species Lasiancistrus tentaculatus. These are fleshy growths derived from the odontode sheaths (Sabaj et al., 1999), which might explain why sexually dimorphism is shown as related clades such as Lasiancistrus shows some clearer dimorphism in the odontodes. In Ancistrus while in the common bristlenose the males display larger tentacles whereas the females display little to none, there are Ancistrus where females have large tentacles, some which have none and some where the size is the same. Not to be confused with odontodes which is why it is best not to refer to them as spines or bristles.

Some factors that are often myths when it comes to sexing Loricariids

Behaviour

It is a common misconception that males are more aggressive then females and often this has no grounding in experience or science, it’s often an assumption. Males and females do have different territories as males are involved in the brood care whereas females roam but where species are territorial it is in both sexes. In territorial species aggression is shown between and within the sexes. Often this idea of males being more aggressive is based in the coy female myth (Milam, 2013; Rosvall, 2013), many scientists have disproved this but Lucy Cooke makes some good approachable books to the topic. Females in Loricariids have no reason to be less aggressive. Personal experience I’ve seen aggression from both and if anything where females tend to roam their aggression is wider spread then close to the caves where males dwell.

The other myth is that females will not use caves, particularly as juveniles they will definitely hide a lot but even as adults females use caves as refuges, they might even have a preferred cave. Males use the caves to spawn in Hypostominae and some Loricariinae but not all do and those that like crevices will use them.

Conclusion

It can be really tricky to identify whether your Loricariid is male or female. Hopefully this offers some ideas to help sex your fishes. I tend to recommend using the abdomen of the fish as I feel this is most reliable and doesn’t leave space for any amounts of individual variation.

For great comparative photos check out: https://www.suedamerikafans.de/en/zur-unterscheidung-der-geschlechter-klein-bleibender-hypostominaer-harnischwelse/

References:

Lujan, N. K., Meza-Vargas, V., Astudillo-Clavijo, V., Barriga-Salazar, R., & López-Fernández, H. (2015). A multilocus molecular phylogeny for Chaetostoma clade genera and species with a review of Chaetostoma (Siluriformes: Loricariidae) from the Central Andes. Copeia, 103(3), 664-701.

Milam, E. L. (2013). Making males aggressive and females coy: Gender across the animal-human boundary. In Women, Science, and Technology (pp. 206-222). Routledge.

Nirchio, M., Oliveira, C., de Bello Cioffi, M., de Menezes Cavalcante Sassi, F., Valdiviezo, J., Paim, F. G., … & Rossi, A. R. (2023). Occurrence of sex chromosomes in fish of the genus Ancistrus with a new description of multiple sex chromosomes in the Ecuadorian endemic Ancistrus clementinae (Loricariidae). Genes, 14(2), 306.

Oliveira, R. R. D., Feldberg, E., Anjos, M. B. D., & Zuanon, J. (2007). Karyotype characterization and ZZ/ZW sex chromosome heteromorphism in two species of the catfish genus Ancistrus Kner, 1854 (Siluriformes: Loricariidae) from the Amazon basin. Neotropical Ichthyology, 5, 301-306.

Rosvall, K. A. (2013). Proximate perspectives on the evolution of female aggression: good for the gander, good for the goose?. Philosophical Transactions of the Royal Society B: Biological Sciences, 368(1631), 20130083.

Sabaj, M. H., Armbruster, J. W., & Page, L. M. (1999). Spawning in Ancistrus (Siluriformes: Loricariidae) with comments on the evolution of snout tentacles as a novel reproductive strategy: larval mimicry. Ichthyological Exploration of Freshwaters, 10(3), 217-229.

Sassi, F. D. M. C., Deon, G. A., Sember, A., Liehr, T., Oyakawa, O. T., Moreira Filho, O., … & Cioffi, M. D. B. (2023). Turnover of multiple sex chromosomes in Harttia catfish (Siluriformes, Loricariidae): a glimpse from whole chromosome painting. Frontiers in Genetics, 14, 1226222.

Eels constantly cause fascination within aquarists but many true eels, Anguilliformes are simply too large for the majority of aquarists. A much smaller but fascinating alternative comes from Cypriniformes, a relatively medium sized genus known as Pangio. I’ve previously owned Pangio for many years and they are one fish I would definitely keep again.

*Pangio myersi* and *Pangio semicincta/kuhlii*

Pangio contains around 32 species (Bohlen et al., 2011), exclusive to South East Asia. They are clearly small anguilliform (the eel shape, not the taxa) but borderline very similar to the larger loach relative, Misgurnus anguillicaudatus (weather loach). For the aquarist the taxonomy can prove confusing with revisions that are not always well known such as the synonymy of Pangio semicincta and Pangio kuhlii (Kottelat, M & Lim, 1993) but is frequently debated seemingly with little explanation as to why (Eschmeyer, 2025). Molecular phylogenetics hasn’t seemed to have solved the confusion, or it’s suggested that the two species are the same (Bohlen et al., 2011). Another problem is Pangio myersi is nested within the two (Bohlen et al., 2011) although easily diagnosed for aquarists by thick barring from dorsal to abdomen (Kottelat, M & Lim, 1993).

There doesn’t seem to be immediately much morphological diversity in this genus, there is a diversity of patterning. While many will attempt diagnosing species by colouration, this has been called into question with solid marked individuals being identified as those with stripes (Bohlen et al., 2011). Like all loaches they contain small scales that to some can make them seem scaleless.

My interest is largely in morphology and like many there seems to be no anatomical studies. The majority focuses in the taxonomic records and this makes it really difficult to understand the morphology that might have ecological importance and also husbandry. We can clearly see a inferior (ventrally facing) mouth so they feed below and given the barbels it seems a common trait with those rooting in the substrate given they are not mobile.

In the aquarium hobby we keep very few species but a diversity is starting to be imported and not just as bycatch. You can expect to find of the distinctively patterned species Pangio semicincta/kuhlii, P. myersi and P. shelfordii. The smallest species that is now being imported in reasonable numbers is Pangio cuneovergata. There are a few solid coloured species and these are likely Pangio oblonga and P. anguillaris, potentially also P. malayana who is shown to have solid individuals.

How to Identify your Pangio?

This is a tricky topic but there are multiple sources that holds clues.

Figure 1: A Key to the Pangio of the Malay Penninsula as described in: Bohlen, J., Šlechtová, V., Tan, H. H., & Britz, R. (2011). Phylogeny of the southeast Asian freshwater fish genus Pangio (Cypriniformes; Cobitidae). *Molecular Phylogenetics and Evolution*, 61(3), 854-865.

As described previously there are some hints you can get from experiencing the species in captivity but there is a lot of cross referencing, where you can linking to a locality and exploration of images that could be of use. I find Bohlen et al. (2011; Fig 1) possibly the most useful of the papers for identification of species even if images are limited. One must also remember where you might have imported from one country it doesn’t mean that is where it is caught.

Habitat

There is little ecological details on these fishes. Habitat likely differs per species. Largely found in blackwater although potentially also highly turbid waters with variable or seasonal currents (Bohlen et al., 2011). Yet in the literature very little else is recorded.

Figure 2: Geographical distribution of Pangio according to INaturalist (2025)

Some assumptions can be made from the locality of these fishes (Fig 2), particularly in reference to temperature, although you will also need to check against elevation and other factors such as is the water body sheltered and therefore cooler. INaturalist (https://www.inaturalist.org/)and GBIF (https://www.gbif.org/) can be useful here although neither make any records of environmental factors. If someone is familiar with these websites then there is other extractions of data that can be done but I am not someone who works with species distributions. Other parameters can be tricky without knowing the geology of the region, some rocks dissolve more readily whereas others allow tannins or just rainwater to drain rapidly through without dissolving minerals.

We also know Pangio almost always seem to breed in tanks with gravel, there are probably exceptions so the substrates must have gravel where they are located with the exception of maybe more elongate species who similar to lamprey bury in silt and sands.

What setup would suit Pangio?

Generally I don’t think the current ideal setup for Pangio needs any adapting, sandy areas and gravel based areas, leaf litter providing many hiding places but also wood or rocks for more solid refuges.

One of my setups in 2017 for multiple Pangio spp., filtered by a Fluval 306 (I think).

A reasonable current but it wouldn’t have to be that strong so a sponge filter would suffice. I would consider with externals, internals or similar filters whether the fishes could get in, they are notorious for finding their ways into filters so either providing an inlet guard or changing filtration method particularly for those like Pangio cuneovergata. Undergravel filters sound great and somewhat are, the fishes will make their way into them and likely also live below the grids but many do report them spawning well there.

There is no doubt these fishes come from more soft acidic water based on locality and therefore I recommend a pH of around 6-7.5 for various reasons. There is flexibility and these fishes have proven themselves very hardy in captivity. Total Dissolved Solids (TDS) below 200ppm but ideally below that 100ppm range unless your water has potentially skewed values. Temperature is definitely the tricky one without knowing exactly the temperature of their caught locality, I would personally cross reference where they are found with water temperatures of the area and who knows other species in the area might have ecological data. Generally 24-28c seems the most ideal but you could be flexible particularly on that upper end to go higher.

They are often noted as being particularly shy although I’ve found with dimmer and dappled lighting but also frequent exposure they don’t seem to be that shy and show a lot of normal feeding and explorative behaviour. Plenty of cover gives them somewhere to retreat to.

References:

Bohlen, J., Šlechtová, V., Tan, H. H., & Britz, R. (2011). Phylogeny of the southeast Asian freshwater fish genus Pangio (Cypriniformes; Cobitidae). Molecular Phylogenetics and Evolution, 61(3), 854-865.

Kottelat, M & Lim, K. K. P. (1993) A review of the eel-loaches of the genus Pangio (Teleostei:Coditidae) from the Malay Peninsula, with descriptions of six new species. Raffles of Zoology, 41(2): 203-249.

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How to Sex your Loricariid (Pleco/whiptail catfish).