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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.

Identifying Corydoradinae Catfish by Ian Fuller and Hans Evers has been long awaited by many catfish enthusiasts whether Corydoradinae is their interest or other Siluriformes. Using the vital recent revision of the genus (Dias et al., 2024) we now have an accompanying book accessible to hobbyists but also enthusiasts.

The revision of Corydoradinae was long needed as in some way resurrecting previous genera and reflecting the previous lineage system hobbyists used, this lineage system was also reflected in the fishes phylogeny/evolution (Dias et al., 2024). Revising the genus Corydoras and subfamily Corydoradinae reflects the morphology/anatomy and ecology better and helps us understand how to keep our Corydoradinae better.

This book offers a modern view at the group brimming with lifetimes of experience and knowledge. I need not introduce the authors as both are extremely well respected not just within Corydoradinae, catfishes but the hobby in general. This collaboration creates the perfect all round collaboration.

The science is always useful to really understand aquariums and how we keep our fishes of which some sources very much lack. Identifying Corydoradinae includes some fascinating science you wont see included elsewhere that is described in an easily understood manner to someone who might not be trained in the sciences. One of the most interesting topics was genome expansion written by Professor Martin Taylor, a scientist who studies the genetic aspects of Corydoradinae. I also very much enjoyed the section on toxins or poisons within Corydoradinae from Professor Eric Thomas as this is at the cutting edge of science, it’s a topic that is not well understood yet this book offers the latest knowledge as to the topic.
For me as having an interest in ecology I was really keen to see mentions as to the fishes ecology and habitats. The ecology section was very useful for hobbyists in describing actually where these fishes are found from experience and knowledge, giving the hobbyist an idea of how to keep the fishes and breed them. Diet has sometimes been misunderstood in the hobby and the inclusion of what we know these fishes feed on is no doubt a benefit. Dr. Luiz Tencatt goes into detail on these fishes diets and hopefully this helps hobbyists know what to feed their fishes.

The layout of the book is useful for the hobbyist as logically passes through the genera before the described species and then the undescribed. This means the hobbyist can quickly identify the species they are most interested in at the time. Brochis is additionally split up which helps identify the various lineages, not completely removing the lineage system therefore the usefulness of it but that would require another scientific revision.

All the species are clearly explained with distributions, size and also detail as to their identification and ecology. To help the enthusiast who might not be too clear on the various genera there is a guide to the various genera and the key features a hobbyist can use to identify them. Plenty of clear images are provided of not just the adults but variants and as the fish ages.

In conclusion, this is a great book with so much detail for any catfish enthusiast. It provides information to help the hobbyists understand a large group of catfishes that can be tricky to identify. Certainly a book you can read in one session but for many years will be of great use.

References:

Dias, A.C., Tencatt, L.F., Roxo, F.F., Silva, G.D.S.D.C., Santos, S.A., Britto, M.R., Taylor, M.I. and Oliveira, C., 2024. Phylogenomic analyses in the complex Neotropical subfamily Corydoradinae (Siluriformes: Callichthyidae) with a new classification based on morphological and molecular data. Zoological Journal of the Linnean Society, p.zlae053.

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