Sort, wash, and spin-dry the mixed salad greens. Discard any large outer leaves.
Wash the radishes, trim them, and slice into thin rounds.
Peel the celery stalk with a paring knife to remove any strings, then slice very thinly.
Peel the pears, halve them, remove the cores and seeds, and cut into thin strips. Using a sharp knife, slice the haddock fillet into thin strips.
Arrange all the ingredients in a large salad bowl or on individual plates.
Whisk together the balsamic vinegar, olive oil, salt, and a few grinds of pepper. Drizzle over the salad at the last moment and serve chilled for maximum freshness.
