The easiest way you can tell male plecostomus from female plecostomus is by looking at their forehead.Female's foreheads are rounded and they are plumpier when spawning while the male's forehead is more flat and more level sloped and more wide in my opinion.Plecos are a fish that clean the algea out of your aquarium.They can even grow up to 12 INCHES!!!!!!!!!

Here are some pics of plecostomuses for you.