When deep frying fish the best temperature to deep fry the fish is between 350 and 375 degrees F.
Use a deep fryer thermometer or a candy thermometer to test the cooking oil temperature in the deep fryer before adding the fish to the deep fryer to get the best results when deep frying fish.
If the cooking oil temperature is too low then the fish may be too oily and greasy and if the cooking oil temperature is too high then you might burn the fish.
I always just cook my fish in Olive Oil in the deep fryer and have the temperature at 375 F which is just perfect for cooking the fish to my liking.
Deep frying fish at 350 F to 375 F takes between 2 and 4 minutes depending on how well done you like the fish to be.
For me 2 minutes of deep frying the fish is more than enough.