If you can't make it to the islands but would like to see some fish,KL Aquarium http://www.klaquaria.com/ is a first-class alternative.
It's one of the newest and smartest attractions in Kuala Lumpur.
You can swim with sharks,get your toes nibbled by garrufa fish and learn all about water in different environments.
There are Discovery Zones with screen projectors with information and facts on the animals exhibited within the Aquaria. Interactive kiosks are also available for visitors to go on a virtual adventure in exploring other exciting creatures that inhabit the world’s oceans.
You can also view the spectacular ocean reef and its inhabitants through a large acrylic window at the Aquatheater. Witness daily fish feedings as well as diving sessions with the sharks.
It's a bit pricey at RM 38 and upwards, but very well done.