Salmon is technically a family, and the different types are sub-families if you want to get really specific.
There is no taxon that is "salmon", and no "technical" way of answering this question, which is fine as-is. It's not necessary to contort the question to exclude "marine" or "vertebrate" or "fish" or "edible" even though you can imagine a way in which these are correct. The question invites you to guess a category based on examples--the best answer is "salmon".
'cycling' not 'cycle'
'skateboarding' not 'skateboard'
'mountain climbing' not 'mountain climb'
'surfing' not 'surf'
'surf' just means that area of the sea by the coast where waves break.