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Has anyone noticed aggresion between diff species of plecs? especially between big guys like royals and commons and smaller ones like clown and BNs? Im planning to get a big tank soon and would like to keep a bigger plec along with 3 or for smaller ones. I have 3 now a BN, Clown and rubbernose and there is no problems their but a bigger guy might cause trouble.

well, i have seen some interesting things. I keep 4 similar sizes plecs along with a few larger and some smaller species. I notice some 'im the boss' behaviour between the fish who are around the same size. My gibby is deffo the boss between the fish equally sized and he will make sure the others wont get any food which is lying near him. But smaller fish can eat from the same piece of wafer... he wont chase them. tbh ive never seen him eating from 1 piece with a larger fish cuz they only show themselfes at night. i think there is only "agression" between similar sized fish.

Hi!

I really dislike using the word aggression...I prefer to use territorial.
Basically every Loricariidae is territorial to its level some are more or less. It also can vary due to the quantity of food available (less food: you have to fight more to have your piece)
the number of individual in the tank (the more crowded the tank is the more territorial battles will occur). Number of shelter,caves: always provide more caves than there are "Loricariidae", the other way around and you will likely see territorial battles...
Hope it clarify a bit
Cheers
Yann