think this a cape moony - extract from web...
Oval Moony (Cape Moony)
Moonies are at home in fresh water and salt water. They occur in large shoals in rivers, estuaries, harbours and in the sea from Tanzania to the Breë River (also reported from Madagascar) and are common off the South African south coast. They are active at night and feed on shrimp and small crabs.
They are sometimes called kite fish because of their shape.