Whether or not Swedish Fish are vegan depends on how strict of a vegan you are.
It also depends on your location (I’ve heard some stories of Swedish Fish containing beeswax in some place).
Here’s the typical list of ingredients in Swedish Fish:
Sugar, corn syrup, modified corn starch, citric acid, white mineral oil, natural and artificial flavor, carnauba wax, red 40, yellow 6, yellow 5, blue 1.
Obviously unhealthy, but to most people those look vegan. As a side note, carnauba wax comes from a plant, some wax is vegan friendly.
But I highlighted the artificial dyes at the end.
I’ve written a detailed guide to whether or not artificial colorings are vegan, but the gist of it is that those artificial colors in particular are all frequently tested on animals. (Mice, rats, dogs, and more).
To ethical vegans, these dyes are not vegan friendly, and personally I don’t consider Swedish Fish to be vegan.
However, I don’t speak for everyone, that’s why I’ve laid out the argument against them, and you can make your own decision.