Sup ikan is basically fish cooked in a clear, mildly spiced broth with aromatics like ginger and lemongrass, soft tofu, tomatoes, and whatever greens the stall has. It's a regular fixture at Malay hawker stalls and nasi campur places, and it's genuinely one of the lightest hot dishes you'll find. At 290 calories with 34g of protein, the clear version is almost unfairly good for a dieter. The fish does most of the heavy lifting here, 150g of cooked ikan jenahak or kembung sitting at 188 calories. The broth itself? Only 20 calories. Fair warning though: these are ballpark estimates. Hard calorie data on Malaysian hawker soups is thin, and the fish portion, oil used, and broth concentration will vary stall to stall.
What actually moves the numbers is what you order with it and how much oil the cook adds to the broth. The clear soup version keeps fat low at 10g, but an asam pedas-style sour fish soup pushes you to 350 calories from the tamarind, chilli paste, and extra oil used in the base. Throw in a bowl of bihun, that's an extra 130 calories bringing you to 420 total. Order it with rice and you're at 580 for the full meal. If you want to stay at the 290 base, eat it plain, ask for less oil if you can, and go heavy on the fish and tofu rather than padding it with carbs.