Hello yes you can eat fish. Dengue patient can have all types of food without any worry. More important fish is good. Keep hydrated also

Hello please consult online for detailed diet plan

You can eat anything you like, there is no restriction in matter of food, only thing you need to remember is during dengue fever there is lot of vomiting sensation so fried food, masalas should be avoided, and spices in food should be kept minimum. So you if you want eat fish better you boil it and make it is curry or soup which should be fine for the patient.