Land before time ...

More than a million years ago, the islands of Sumatran, Java and Borneo and other smaller Indonesian islands were connected to Peninsular Malaysia on mainland Asia, forming the Sundaland. Geographical research has shown that Sundaland would include the southern tip of Thailand, the whole of Peninsular Malaysia, Borneo, Sumatra and Java.
 

Sea levels were significantly lower but suddenly rose during the Pleistocene. The connections to the mainland were covered by waters, leading to the formation and isolation of the islands.

Therefore, would it have been possible that the major rivers in modern Peninsular Malaysia, Sumatra, Borneo, Thailand and Cambodia were connected to form a major river system in Sundaland that hosted arowanas in its numerous rivers and lakes? As sea level rose, these rivers and lakes were disconnected when the land bridges disappeared. Could it be that the arowanas in each isolated river and lake further evolved to become the different arowana varieties that we know today? (hint: green arowanas are known to be found in Thailand, Cambodia and Tasek Bera Lake, Endau River and Trengganu drainage area).

Disposing your arowanas

A silver arowana in a man made pond.

Many people bought young arowanas when they were merely 6 or 7 inches long to raise as pets as they believed arowanas to be auspicious and beneficial for their feng shui. These infant arowanas eventually grew up, up to 3ft long and often  require bigger tanks as the continued to grow. In land scarce Singapore where majority of the population lived in HDB flats, having big 5ft tanks to house a 3ft arowana can be quite a challenge. It could get to a point where desperate owners tried to sell or even release them in manmade ponds or reservoirs. In many cases, these fully grown but abandoned arowanas thrived and continued to breed. 

I personally do not think these arowanas should not be released in the wild or in reservoirs as these are not native to Singapore. They could be donated to the Singapore Zoo especially so when the River Safari (a river themed wildlife park) has recently opened. This would be a more humane way of disposing your pets rather than to dump them into the wild and upset the ecological balance.

A pair of yellow tail arowanas in the Singapore Zoo

Of course, you can also choose to sell them off in your friendly LFS or over Ebay :P