Before that question can be answered one would need to know what kind of catfish you are asking about. There are so many different species that are called "catfish" that it is impossible to make a generalisation.
There are many different species of fish that are called "Catfish" Some have easy to see sexual differences and others show no difference between the sexes at all.
Catfish mate in the springtime, in warm water. The type of insemination that is most common tends to be internal. The male catfish may place his sperm in the oral cavity of the female catfish, and...