Why are you worried about this? Seems like there are two possibilities, based on what you've said about there being no info on it:
1) You're opening up a can of worms (ha!) that no-one else has thought of yet, and you'll be credited with alerting everyone to the dangers inherent in canned fish
2) The reason you can't find any information about it is that it isn't a problem.
Before I can guess which is correct, I need to hear what lead you down the path of thinking this could be a problem.
Zone diet on and off for several years....worked, but too much focus on exact meal composition
Primal since July 2010...skinniest I've ever been and the least stressed about food