Here are somes snakeheads that might work as a couple:
-Channa gachua (different types)
-Channa orientalis
-Channa spec Assam (Lal Cheng)
-Channa bleheri
-Channa spec 5 stripe (spec Kerala)
-Channa stewartii (close to the limit)
-Channa bankanenis
-Channa panaw
-Channa punctata (Close to the limit)
This are just species...........I do no know how expierienced you are........!!
Because some of them need special waterparameters....so inform yourself about the species BEFORE buying!
By the way: 240 litres could be everything!
For snakeheads it is important how much ground the tank has!
It is not neccessary to have a lot of hight!
But the lenght and the depth is important!
So what are the measurements?
1m long x 40 cm deep x 50 cm high???