1. Mix tomatoes, broth, chopped fennel bulb, garlic, oil, saffron, if desired, basil, and purple pepper flakes in gradual cooker. Cowl; cook dinner on low 4 to five hours or on excessive 2 1/2 to three hours, or till fennel is tender.
2. Stir in halibut or cod and shrimp. Cowl; cook dinner 15 to half-hour, or till shrimp is pink and opaque and fish begins to flake when examined with a fork. Ladle soup into shallow bowls. Garnish with chopped fennel fronds.