how big do bristlenose catfish have to breed?

Answer 1

Deopends on what species you have, some Bristlenose only get about 3" other exceed 6" or more. Obviously the larger species are going to breed at a larger size. Here's a link to pictures of some of the more common species that might help you figure out which you have.

http://www.planetcatfish.com/catelog/index.php?task=&genus_id=4&family_id=4

Hope that helps

MM