Are these grocery store oyster mushrooms OK to eat? I bought these at the grocery two days ago. They have been in the fridge. They are firm. The white fungus in the gills is firm too. No bad smell. Can I cook and eat?
They're likely mycelium rather than other moulds, its not uncommon for certain varieties of stored mushrooms to start producing mycelia (the root system of mushrooms generally). According to this link, mould on mushrooms is more likely to be green,black or brown

http://www.gourmetmushroomsinc.com/fresh-restaurants-faq.htm