I bought ten Otocinclus affinis for my 75 a couple of months ago, and they totally cleaned it up of algae. I lost one recently and was worried about starvation, so I put three of them in my 38 two weeks ago. The tank has a bunch of vals, crypts, naja, wisteria, and a very "healthy" coating of brown algae. The otos loved the move, and I noticed one of them get really, really fat. So fat, I was worried about dropsy.
Fast forward to yesterday morning. Made my cup of joe, sat down to watch the fish, and I see some strange behavior on a Val leaf in the front of the tank. Sure enough, it is that really fat oto. Wait, what is wrapped around her? It's the male, who literally has her wrapped with his entire body. Her ovipositor is extended, and they are doing an awesome dance up and down the bottom side of the leaf. Then they move to the underside of a crypt leaf. So cool! I am super excited, and yell to my wife, who really isn't all that interested. I didn't see any eggs, but the darn Pseudomugil gertrudae that I picked up last weekend (cool fish!) are following the pair around. Darn! I hope some eggs survive. It would be so cool to have some little otos swimming around! I may have to set up a 10 gallon algae tank for them.
Crappy cell phone picture with just the female follows. Can you find her? Front of tank on a crypt leaf. Note light coating of brown algae on the glass.