The Climbing Perch. This guy lives in the well and was kept in a glass of water, while the well was cleaned up. Apparently they can live for a few days out of water. Found in water around paddy fields and streams in Sri Lanka. They were abundant many years ago and now their numbers have depleted due to pesticides in the waterways. During the rainy season, it will swim upstream. (info from Karunaratne Weerasooriya).
See here for complete list of Sri Lankan fresh water fish.
Apparently "the kavaiya is a fish and ergo a flag with a kavaiya depicted on it is the Makara Kodiya."