I heard that common plecos catch and kill smaller fish or suck the slimecoat on my other fish, is this true? The other way is to inspect the genital papillae. I have read from various sources that large males have thickened pectoral fins that can have a red looking colour to them. The pardalis has a spotted pattern whereas the disjunctivus has a vermiculated pattern. There isn't really much difference apart from the pattern on the tummy. How can I tell the difference between the pardalis and the disjunctivus? If you count the rays and they add up to more than 10, then it is very likely the pleco is a Pterygoplichthys and all the plecos in this family grow to be very large. Have a look at the dorsal fin(the fin on the top of the plec). How can i tell that the cute baby pleco at the fish shop is going to grow up to be so big? This plec really is unsuitable for most aquariums due to the space it needs to grow and be happy. The pardalis and the disjunctivus are excellent algae eaters especially when they are young, the downside is that they both grow to over 1 foot long in quite a short time, most certainly under a year given the right care requirements. These are two very similar pleco's, the L021,L023 Pterygoplichthys pardalis and the Pterygoplichthys disjunctivus. There are a few pleco's that are given the 'tag' common pleco, the two i'm providing info about are the most likely 'common' plecs that you will see in the LFS. Here is some info, care requirements and photos for 4 top algae eaters. I've written this guide which will hopefully help answer the question and also help avoid getting large plecs that are not suitable for the average size aquarium. So many people ask 'What is a good pleco for keeping algae down in a fish tank?'