For the moment concerning snakeheads, I have an unknown snakehead and a channa Marulius.. I badly want a red/giant snakehead. By the way may be you can help me ti ID the unknown snakehead.
They are a very nice species but they don't get very big . Yours looks to be almost full grown the species only reaches 12" (give or take depending on locality)
Also I feel I jumped the gun a bit on that first guess because the fish originally pictured could also be channa maculata , they look very much like argus but are a tropical species given your location if there is a feral population of them and it's not just someone's big pet then it's more likely that it's maculata.
Both argus and maculata have been introduced in many places for use as a food source both intentionally into rivers or accidentally by escaping farms.
Also channa striata is known to have been introduced to Madagascar and neighbouring islands which would make then them a likely candidate, the jaw shape looks too pronounced for striata to me, but that could be the result of the angle.
In curious , Is it a common find I your waterways?? Would another pic be possible?