depends on the breed some are really hard to tell. for those you place pleco caves in the tank and see which ones go in them. only the male will choose a cave and guard it.
others like bristlenose are easier the males get a face full of bristles and the femles usually only have a few on the side of the face
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Are these dwarf plecos or could they be juvenile leopard plecos? The newly started shop where I got them from called them "Chinese sucker-mouths" but I couldn't find any detail on them from the net.
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