Mediterranean Fish Stew with Shrimp and Cod

1 tbsp olive oil
2 onions, peeled and medium diced
1 bulb garlic, peeled and rough sliced
1 cup celery, medium diced
1/8 tsp fennel or anise seed

4 tbsp tomato paste
2 cans diced tomato plus juice

dry sherry
shrimp stock (see recipe)  OR other seafood stock, including clam juice
oregano
1 very large pinch saffron threads
2 oranges, juiced
kosher salt

cod, diced
shrimp, peeled and deveined
parsley, chopped (opt)

chile garlic paste (optional)