Ca kho to is 300 calories for a normal quan pot and 30g of it is protein, which makes it one of the better lauk on the tray. The published figure is about 120 calories per 100g of braised fish, and a two piece pot holds 150g of fish, so 190 from the fish alone. The rest is the sauce: nuoc mau is sugar cooked to caramel, and a pot uses about 20g of it plus fish sauce, so 60 calories of sauce that you will pour over your rice.
The fish choice changes the number a lot. Ca loc (snakehead) and ca ro (climbing perch) are lean, around 100 calories per 100g cooked. Ca basa and ca hu, the catfish cuts with the belly and skin, are 180 to 200 per 100g because the fat renders into the sauce. Same size pot, 300 versus 420. Ca kho with thit ba chi, where cubes of pork belly are braised in with the fish, is 480 or more.
The meal is the issue more than the fish. Ca kho is so salty and sweet that it is designed to push rice: most people eat 300g of rice with one pot, which is 390 calories, plus the sauce soaked into it. A pot of ca kho, a big plate of rice and a bowl of canh chua is 850. Take a small plate of rice and the same meal is 650 with the same 45g of protein.