At about 2" of length is when you will start seeing signs of mating depending on grow out diet. When a male gets a decent amount of bristle on its snout at some point it will take "a cave". Bristle nose are prominent breeders and will even breed in a crevice and underneath decoration. Once the male has found a suitable home to raise fry he is ready. The female will begin to get very very plump otherwise "gravid" with eggs. There is a clear difference in a well fed bristle nose and a gravid female. Once the female starts fattening up the next step will be to watch for the male fanning his fins face first in the cave. It's a method used to bring the female to the cave. Generally within a week or two of this you will find a female hanging out around the cave and then a ball of eggs in the back, closed off end. Like the previous post said cold water helps trigger the first few spawns. My advise.... Along with baby brine crush up finely, a quality shrimp mix flake with at least 50% protein for your babies and feed this to you currant plecos as well. Bristle nose love all types of food. They really love fresh veggies and meaty mixes