As nouns the difference between troop and shoal
is that
troop is a collection of people; a company; a number; a multitude while
shoal is a sandbank or sandbar creating a shallow or
shoal can be any large number of persons or things.
As verbs the difference between troop and shoal
is that
troop is to move in numbers; to come or gather in crowds or troops while
shoal is to arrive at a shallow (or less deep) area or
shoal can be to collect in a shoal; to throng.
As an adjective shoal is
shallow.