otocinclus will at least be very social. those little fellas will jump right in with darn near any other schooling, active, or social fish. think they just like company.
Like dixon said.
i have had Ancistrus sp., Panaque sp., Peckolita sp, and Hypostomus sp all play nice together (along with the otocinclus sp.) Conversely some hypostomus are just nasty as they develop size and stop playing nice. probably something to do with territory/food.
I also have a Baryancistrus sp. that plays mice with all the above.
i have had Hypoptopoma sp. and think of them as anti social. may have been the specimens.
I have a Pseudacanthicus sp (Papu) that plays nice with several of the other species listed above--he is young yet.
as to aggression among plecos. yes it happens--even with a species like bristlenose. i have seen bristle nose beat the bejeebs out of one another. i have seen them be very friendly. depends upon the specimen as much as the species at times--just like any other fish.
Royal farlowellas (not really a pleco) get along fine with others--they know how to play nice together.
i guess i will say that the otos are the only species i think of as "schooling". Or, really--highly social.
at feeding time many of the species have no problem getting any other fish in the way of their dinner out of the way.
