Honestly, 200 calories is pretty decent for a stir-fried veg dish. The kailan itself costs you almost nothing, around 40 calories for 120g of cooked greens. Where it sneaks up on you is the oil. A wok fry absorbs roughly 14-15g of oil, and that alone is 110 calories. The salted fish adds another 40. So you're basically paying 150 calories just for the cooking method and flavour. Fair trade if you ask me. The ikan masin is genuinely tasty and you get 9g of protein from a veg dish, which is not bad at all. These numbers are ballpark estimates by the way, because there's not a lot of hard lab data on kailan ikan masin specifically. Different hawkers use different amounts of oil, and the ikan masin portion varies a lot. Treat this as a reasonable guide, not a precise count.
What actually changes the maths here is the oil, full stop. A hawker who woks hard and generous can easily push this past 250 calories. A lighter hand stays closer to 160. The size of your scoop matters too. A heaped plate versus a small side scoop can be a 50 to 70 calorie difference. Some places also add a bit of sugar or extra oyster sauce, which adds maybe 15 calories but a tonne of sodium on top of the already-salty ikan masin. If you're watching your calories, this is still one of the safer dishes to order at a mixed rice stall compared to masak lemak or rendang. Grab a big scoop of this instead of an oily gravy veg and you're already doing better lah.