Amok Trey is freshwater fish in a spiced egg mousse.
It is not too foreign to us, as it is similar to the local nyonya otak-otak, but quite different in many ways.
One of the important ingredients in amok trey is again, prahok. You can substitute it with other ingredients like fish sauce or shrimp paste, but I personally find the flavour profile to be quite different. The other special ingredients used is fingerroot (krachai, temu kunci).