Fishing industry
75% of home-caught fish is exported, and the majority eaten in the UK is imported.
Result: Bad
We import large quantities of prawns and tuna from the EU, and the main export is mackerel - which will be effected by tariffs.
Many fishing businesses campaigned to stay within the EU because they rely on exporting to the EU; but some campaigned for Brexit because they were against the controls on fishing quotas.
The limits are there to preserve our fishing stock, and are unlikely to "improve" outside of the EU.
Interestingly Grimsby, which voted 70% to leave the EU, is now asking for special dispensation, in an attempt to be a "free port", so they can avoid 0-25% import tariffs, and customs delays.
If you disagree, or would like to add more details, please let me know.
You can suggest a reason for leaving the EU, or look at the other reasons.