First soak the fish in water for 24 hours with 4 or more change of water to remove the salt from the fish.
Boil the potato and fish separately and set aside.
Heat olive oil in skillet and add chopped onion and serrano pepper cook until onion becomes translucent then add ginger-garlic paste and spice powders like cayenne pepper, turmeric , coriander powder and fish masala. You can use paprika and Cajun seasoning if you don’t want too spicy.
Then add fish and cook for another 1 minute and then add mashed potato cook until everything combines well and form smooth dough.
Then divide the dough into 11-12 equal sized pieces and hold in the palm and make it into cylinder shape. If you make cylinder shape that will help you to shallow fry them.
Then coat them well with panko bread crumbs.
Then dip them into all purpose-mixture and roll them in panko bread crumbs once again and set aside.
In a skillet heat peanut oil and fry the croquettes make sure to flip gently on each side and fry them until it become golden yellow color.
Since I used panko bread crumbs shapes are not uniform. If you use fine bread crumbs it will looks better.
Serve with tomato ketchup or your favorite sauce.