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Shane's World Right Arrow Catfishology Right Arrow The Catfish Basics Series, Part 8 • Telling the Boys From the Girls • Article © Shane Linder, uploaded January 01, 2002

Photo credits for the images used in this article can be found on the respective Cat-eLog species pages.

One of the most frequently asked questions here at Planetcatfish is, "How do I tell if my fish is a boy or a girl?" In scientific terms, we refer to the physical differences between males and females as sexual dimorphism. Sexual dimorphism is well known for several families of catfishes based on scientific information and information made available to the hobby by aquarists that have spawned different catfishes. In some families all members of that family exhibit the same physical differences between males and females. For example, all male bagrids posses a genital papilla that is just fore of the anal fin. Female bagrids lack this papilla and are also more robust overall when gravid since they are full of eggs. However in other families, such as the loricariidae, different genera have their own sexually dimorphic characteristics that may not be applicable to other loricariid genera. The goal of this article is to provide some guidance on telling the boys from the girls amongst the families most commonly spawned by aquarists. One word of warning though, don't expect to be able to walk into your LFS armed with this article and expect to come home with a pair of catfish. Relative to other aquarists, there also seems reluctance by aquarists to sell mated pairs of fish. While pairs of cichlids or killifish for example can be found for sale as such, pairs of catfishes are not be expected for sale as such. It's up to you to figure that out! As with most fish for sale, youngsters are the most common fish found for sale and most do not yet show or are to small to determine, your best bet is to buy a group and use this guide as they develop at home.

This is, by necessity, a very general, introductory article but we need to use two rules of thumb before we look at the specific differences shown by different groups of catfish. First of all, you need to identify you catfish at the very least to the family it belongs to but preferably to a genus or best to a particular species. Secondly, it is unusual for sexes to be able to be accurately determined with young fish. You fish should be at least half grown. Generally the larger the species grows, the easier it is to tell at an smaller size. Some species however remain hard to tell apart even when adult and some only show sexual differences at certain times of the year when the fish are in reproductive condition. With all that in mind, read on.

Aspredinidae - Banjo Catfish
Platystacus cotylephorus
Male
Platystacus cotylephorus
Female
Females are typically larger and more robust then males. Some differences in coloration between the sexes have been reported amongst a few species such as the Eel Tail Banjo (Platystacus cotylephorus) shown here. Male, left, is more slender and has a brighter tail colouration. Female, right, is most obviously more robust but also has a lesser colouration. Note how much easier it is to tell the female when viewed from above. As a good case in point, this species can appear in anything from matt black to dusky pink in colour and this doesn't appear to have any bearing on gender.
Auchenipteridae - Driftwood Catfish
Centromochlus perugiae
Male
Centromochlus perugiae
Female
Auchenipterids are very interesting for their unique differences between the sexes. The anal fin of males is modified into a copulatory organ much like the gonopodium of live bearing fish. This organ is used to deposit a spermatophore into the female's urogenital opening during spawning. Many male auchenipterid species develop enlarged and elongated spines, especially the dorsal spine, during the spawning period and use the spine to hold the female while the spermatophore is deposited.
Centromochlus perugiae
Male
Centromochlus perugiae
Female

Bagridae
Bagrichthys macracanthus
Male
Bagrichthys macracanthus
Female
Male bagrids posses a genital papilla just fore of the anal fin that is reminiscent of the gonopodium of live bearing tooth carps. Female bagrids, especially when gravid, are also much more robust overall then males. This feature is only really useful for determining fish that grow larger than a few inches. On smaller species, like Hyalobagrus, one must go on size / girth alone although these fish take a much shorter time to reach maturity and can be more easily kept in shoals until such a time as they mature.

Callichthyidae - Corys and kin
Corydoras sp. CW044
Male
Corydoras sp. CW044
Female
Subfamily Corydoradinae - The subfamily corydoradinae includes all members of the genera Corydoras, Aspidoras, Brochis and Scleromystax. In general, males reach an adult size of about three-fourths the adult size of a female of the same species. Females are also much more robust and, when viewed from above, appear much wider than the "skinny" males. Males fins also taper to a point; females are more rounded. Mature males of the genus Scleromystax can be distinguished from females by their cheek spines as well. At least two groups of corydoradinae also exhibit sexual dichromatism (meaning males are a different colour pattern than the females) such as with Scleromystax barbatus or Corydoras elegans.

Subfamily Callichthyinae - Hoplos etc. This subfamily includes Hoplosternum and Megalechis. Mature males of these genera sport thickened, and often elongated, pectoral spines that distinguish them from females. The pectoral spines of the male will also often curve upward and may become reddish / orange in colour. When viewing the belly of the fish in the region of the "chest", you will observe a plate like structure called the coracoid process; with a bit of imagination it looks like a waistjacket. In males this is touching or nearly touching, in females there is a distinct gap. This page shows a fully developed male's underside - note the thickended fin rays, bristles on fin tips, fatty pectoral fin growth, genital papillae and the coracoid process. Other common genera, such as Dianema, are much harder to determine as they do not show such features and gender is determined on size alone.
Megalechis picta
Male
Megalechis picta
Female

Doradidae - Talking or Raphael Catfish
Agamyxis pectinifrons
Pair, male below
Megalodoras uranoscopus
Pair, female below
Females are larger and more robust appearing "plumper" than males when viewed from above. That said, these differences can be difficult to see unless a group of adult fishes are compared side by side. Larger fish are easier to sex by examining the genital papillae underneath the fish, mind you, getting close enough to photograph a large doradids private parts is an article in itself!
Megalodoras uranoscopus
Male
Megalodoras uranoscopus
Female

Loricariidae - Plecos
Many, if not all, loricariids, posses some form of sexual dimorphism. Unfortunately for aquarists the physical differences often only manifest themselves during the spawning season and then disappear.

Subfamily Hypostominae - includes virtually all L-numbers and many more described species.
Ancistrus sp.
Male Ancistrus
Ancistrus sp.
Female Ancistrus
The tribe hypostomini lack the evertible cheek spines of their ancistrini cousins. They also, as a group, are amongst the most difficult loricariids to sex. In general, females are larger and more robust. Male Hypostomus may, during the breeding season, develop slightly enlarged and reddened pectoral spines. In some ancistrine genera, such as Panaque, Hypancistrus and Peckoltia, these cheek spines are greatly elongated in males. The males of several genera, such as Panaque, Pseudolithoxus and Acanthicus sport large spines, or odontodes, along their pectoral fin during the spawning season and some Panaque males are so covered with odontodes from their dorsal fin back to their caudal peduncle with odontodes that they look "hairy". Contrastingly with many other catfish, the males are often bulkier across the head and shoulders area with females less developed but with the usual lower body girth. Male Ancistrus possess tentacles along their head. In some Ancistrus species the females may also possess tentacles, but these are not as pronounced as those of males. Male Chaetostoma have elongated pelvic fins and, during the breeding season, their rostrum becomes swollen. Hence the common name "rubbernose" pleco for Chaetostoma. Ingo Seidel's article on this group of fish goes into detail should you want to find out more.
Peckoltia sp.
"Hairy" male & "bald" female Peckoltia
Panaque cochliodon
Male "cheek spines" or odontodes

Subfamily Hypoptopominae - Dwarf Plecos
Otocinclus cocama
Male
Otocinclus cocama
Female
This subfamily includes Otocinclus, Hypoptopoma and Parotocinclus. These smaller loricariids show few signs of sexual dimorphism but gravid females are usually easy to spot because of their plump appearance.

Subfamily Loricariinae - Whiptails etc.
Sturisoma aureum
Male Sturisoma - cheek spines
Hemiloricaria teffeana
Male Hemiloricaria - head and pectoral spines
This subfamily includes what I call the "flat plecos" such as Farlowella, Sturisoma, Hemiloricaria and Loricaria. The members of the subfamily can be divided into two general groups - the egg guarders and the lip brooders. Amongst the egg guarders we encounter Farlowella, Sturisoma and Hemiloricaria. Depending on species, sexually active males posses odontodes on any combination of their cheeks, rostrum, pectoral fins or head. Male lip brooders have a specially adapted lower lip that is greatly enlarged.

Mochokidae - Synos
Synodontis notata Synodontis notata Synodontis notata
Pair, female above Male Female
Synodontis and their kin are not always easy to sex. Typically females are larger and more plump, especially when laden with eggs. Male Synodontis possess a 3-4 millimetre genital papilla.

Pimelodidae - Antennae Catfish, Ictaluridae - North American Catfish, Ariidae - Shark (or Sea) Catfish, Pangasiidae - Pangasius / Iridescent Catfish
Commercial fishery records show that adult females are always longer and heavier than adult males in the larger, farmed for food species. That said, these fish are usually found for sale to aquarists as young fish and sexing them at this stage in their development is largely impossible due to the time it takes for them to mature - many of these fish, despite being commonly offered for sale, are really too large to keep at home successfully. Keeping them alive for something approaching a natural lifespan is a big enough challenge without thinking about reproduction, which, is often out of the question due to migratory requirements.

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