A 500 gallon tank could house a good colony of L200s, or some L14s. I believe both have been bred in captivity though L14 was an unknown trigger. Either way, you could do a lot of awesome plecos in a tank that size. But for breeding purposes, unless you have a huge amount of bristlenose, it is pretty much a waste. You won't be able to pull the fry safely and many will die. For larger plecos like the L14, or the L114, or L240, this tank size would be perfect.