Add cubed fish, spices, and rum into a ziploc bag or container. Let this marinate for a minimum of 1 hour in the fridge, the longer the better.
Heat a pan on medium heat, add 1 tbsp butter to pan fry fish cubes. Cook for approximately 3-5 minutes stirring frequently and add 1 more tbsp of spices. Cook only until fish begins to flake apart and remove from heat.
To prepare to serve, warm taco shells or in oven at very low heat for 2-4 minutes. Remove from heat and begin fill with cooked fish and desired toppings.