Whenever I see a clue like 'small salmon' in a puzzle, I grin because it's one of those tidy little moments where natural history and wordplay meet. Smolt is literally the biological term for a young salmon that has migrated from freshwater down to the sea — it's the stage after being a fry and before growing into an adult. So on the surface the clue is simple definition: 'small salmon' = smolt. That straightforwardness is why setters like it; it's precise, not fuzzy, and it teaches solvers a neat bit of life-cycle vocabulary.
What makes 'smolt' especially crossword-friendly is also its construction. In cryptic-style thinking you can parse it as S + molt: 'small' often clues the single letter S, and 'molt' means to shed or change — combine them and you get 'smolt', which also happens to be the name of that juvenile fish. I love that double layer: a natural-language definition and a tidy charade. Beyond puzzles, the smoltification process is fascinating — hormones trigger physiological changes so the fish can handle saltwater — and learning that tidbit feels like getting a tiny ecology lesson tucked inside a leisure puzzle. I always finish a puzzle with a richer mental aquarium, and smolt is one of those words that sticks with me, especially during spring when rivers are full of migrating juveniles. Pretty cool little word, honestly.