I suppose the most asked question I get from Corydoras keepers is, 'How do I sex them'. A simple enough question you may think but the answer is never quite as easy as that. There are several factors that need to be looked at, with a lot depending on the species involved.
There are three main areas of difference, Body, Fins and Colour. When buying new stock it can often be a very difficult task to determine the sexes, freshly imported fish can be especially difficult depending on their overall condition on arrival. Newly imported fish are often under fed, having been kept in holding tanks awaiting dispatch, sometimes going for weeks on end without any food at all. In such cases it is a good idea to buy at least six specimens and condition them up. Generally speaking Corydoras are hardy little creatures and it does not usually take very long to get them into reasonably good condition, making it far easier to determine the sexes.