This is a subject that keeps cropping up time and again so I thought I would make this a sticky for all to check out before asking the question.
1. Body. Generally females grow to a larger size than males.
2. Body. Females when in good condition are plumper than males. When viewed from above the widest point of a females body is at a point level with or slightly to the rear of the ventral fin spines. In males the widest point is level with or slightly behind the pectoral fin spines.
3. Fins. The ventral fins of the males tends to be more elongate and pointed, where as in females they are fan shaped and rounded. This feature can vary from species to species and in some cases there will be no visible difference.
There are some species where the dorsal and pectoral fins are greatly extended in the males.
4. Colour. Although colour is not a dimorphic feature in all species there are a number of species where colour is the major difference, this is mainly within the so called "elegans" group and some members of the genus Scleromystax, (S. barbatus, S. kronei etc).
5. Secondary dimorphism There are a small number of species that have a permanent secondary dimorphic feature, this is in the form of cheek odontodes (bristles). These species are, S. barbatus, S. kronei, C112, C113, C. geoffroy & C. macropterus.
Males of the so called curved or saddle snouted species also display seasonal secondary dimorphism in the form of extended growths of odontodes on the pectoral fin spines, although these are evident in both sexes to a greater or lesser degree, it is during the breeding season that the males become extended and bushy.