I'm a professional chef.
Any clean oil will work.
Keep temp. around 360-365.
Don't overload.
Buy a candy thermometer-glass tube type-7 bucks.
Watch for debris accumalation in bottom of pan on a stovetop burner.
frozen fillets will float when done.
fresh fillets(depending on size)will take 4-7 minutes.
Probe style thermometer(6-10 bucks) will give you an internal temp of around 160 when done