you can buy many wild caught cichlids and l number plecos from the Amazon, as well as other fish from different areas of the world. I have just set up a hillstream loach tank and most (if not all) of the specimens I am buying will be wild caught as it is very hard to breed them. As long as you acclimatise correctly then yes you can do it. The only other thing to watch out for is bringing diseases into your system. Wild fish will have tolerances to different bacteria and vice versa. It is therefore best to quarantine wild caught species for 1-3 months.