For slaw: In a screw-top jar, combine vinegar, oil, tarragon, mustard, the 1/8 teaspoon salt, and the dash black pepper. Cover and shake well. Set aside 1 tablespoon of the vinegar mixture; cover and chill until serving time. In a large bowl, combine fennel strips and carrot. Pour the remaining vinegar mixture over fennel mixture. Toss lightly to coat. Cover and chill for 2 to 24 hours.

Thaw fish, if frozen. Rinse fish; pat dry with paper towels. Measure thickness of fish. In a small bowl, stir together crushed fennel seeds, the 1/2 teaspoon salt, and the 1/4 teaspoon pepper; sprinkle evenly over both sides of each fish fillet.

Place fish in a well-greased grill basket or in a greased grill wok. For a charcoal grill, place grill basket or grill wok on the rack of an uncovered grill directly over medium coals. Grill for 4 to 6 minutes per 1/2-inch thickness of fish or until fish flakes easily when tested with a fork, turning basket once or carefully turning fish once halfway through grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place fish in well-greased grill basket or in greased grill wok. Place grill basket or grill wok on grill rack over heat. Cover and grill as above.)

Drizzle the reserved 1 tablespoon vinegar mixture over grilled fish. Serve fish with slaw. If desired, garnish with fennel tops.