Striped Bass with Lime Broth

Toast coriander, cardamom, and curry paste in a medium saucepan over medium heat, stirring, until spices are fragrant and curry paste begins to caramelize, about 2 minutes. Add cilantro stems, kaffir lime leaves, fish sauce, and 1 cup water. Bring to a boil, reduce heat, and simmer gently until flavors meld, 8-10 minutes. Strain broth through a fine-mesh sieve into a large heatproof measuring cup; discard solids. Let cool, then stir in lime juice; season with kosher salt and more lime juice, if desired. Meanwhile, using a sharp knife, cut all peel and white pith from grapefruit; discard. Working over a small bowl, cut between membranes to release segments into bowl; discard membranes. Repeat with lime. Heat vegetable oil in a large cast-iron or other heavy skillet over medium-high heat. Season fish with salt and pepper. Cook fillets, skin side down, 1 minute, then firmly press down with a fish spatula to ensure even browning and crispiness. Continue cooking until skin is golden brown and fish is mostly cooked through, about 4 minutes; carefully turn fish and sauté until just cooked through, about 1 minute longer. Divide lime broth and fish among shallow bowls. Scatter citrus segments, cilantro leaves, and mint and basil over; drizzle with olive oil and season with sea salt. DO AHEAD: Broth can be made 1 day ahead (do not add lime juice). Cover and chill. Bring to room temperature and add lime juice just before serving.