Like but not identical, look at the caudal fin. On one fish the black caudal blotch strays well onto the fin and in the other it does not. Also the back patterning looks different, but this can be very misleading as it changes with mood/conditioning. There are some other minor differences.
I've spent many hours trying to ID various
Otocinclus using external characteristics and it's very hard, usually impossible especially if you do not know what part of South America they came from.
The irony of all this is that the easiest to ID member of the genus (the zebra oto) is not described! (Yet).
Jools