Sometimes I open sardine tins and the tomato sauce is pure smooth red and every now and then there are cans with what looks like plaques where bacteria colonies might be growing. What are these specs? Can I eat this?
The white specs are not colonies of bacteria, but in fact, crystallized oils. This phenomena is common in many tinned fish rich in fatty oils. This is normal and completely safe to eat.
If it bothers you too much, you can try reheating it, which should dissolve the crystallized oils back into the sauce. Just remember not to microwave anything metal.
This link provides some information about it too. http://ayambrand.com.sg/mackerel/46-about/frequently-asked-questions/about-our-quality/37-what-to-do-with-the-fish-oil-white-particles.html