Congratulations and good luck.
How do you know their gender?

Nice...
What kind of otocinclus is?

what do you mean by "ridge"? If you mean that ridge is what it has the fish in the second photo on its head I am sure that the first fish has not it... Ridges have only in front of its mouth and not on its head and between its eyes. I think that means that it is female.. Maybe the foto is ...

Are you sure that the first is not an Ancistrus cf_cirrhosus?
They sold it to me like an Ancistrus cf_cirrhosus that 's why I 'm asking.
Also,the first is female and not male.
Thank you very much.

Hi.
I 'm new here and generally in this hobby...
I have in my aquarium 3 plecostomus and I am not sure about their kind.
Can you help me?