Fish is actually an excellent protein for dogs - so don't worry about that part - the protein source is a great one!
But you absolutely *do* need to balance the diet correctly and have the correct supplementation for whatever is missing.
But here's an easy way to "homecook" - get U-Stew or similar - and all you have to add is the fish - that's it - balanced!
Here:
https://www.knowbetterpetfood.com/co...-stew-for-dogs