Hi all,
I've been in London for a few days sight seeing with the kids, and managed to get them to Kew Gardens. In the marine display (underneath the "Palm House" <http://www.kew.org/visit-kew-gardens/garden-attractions-A-Z/marine-display.htm>), there are a couple of fairly large tanks with brackish water fish, including a tank with Green Chromide.
A pair of these have spawned and were protecting a large number of small free-swimming fry against all comers, with all the other fish penned in the top third of the tank.
The pond in the Princess of Wales Pavillion Tropical zone is also well worth a look (particularly for those who like large fish).
cheers Darrel