Thanks! I don't know the species very well, but I would prefer the 3 spine because I know they get colorful when breeding (red bellies, blue eyes) and they are a larger species. Other species may also, but I am not sure. The brook stickleback seems a bit drab to me but perhaps the pictures I found don't do it justice. I'd like to keep to the more-freshwater species if possible, but a pair of fifteen spines would be cool! I checked aquabid yesterday but wasn't able to find any current listings.