Though it could be the zoom on the camera, the photographer seems really close to water and these guys show no concern to a potential predator. I'm thinking either tilapia don't care about predators and the standing water is fed by a stream or canal carrying something they're eating, or they're accustomed to human presence because they're being fed.
When I see the escalator pic all I can think of is how are the fish surviving all the toxins, like oil for the escalator and chemicals used through out the mall. My best guess for food is as someone stated that stagnant water is going to attract all kinds of insects,I would include a fair share of rodents. Just like in a lake I bet the fry from breeding pairs are a welcome treat I am sure there is plenty of algae and looks like some sort of plant life in some of the shots.
Eventually these fish are all going to die off and poison the surrounding area check out the history of the sultan sea.