Reactants? The chemicals needed to start a chemical reaction.
Fish fossils occur in sediments deposited underwater. That could be sea bottom, lakes, or rivers. Generally, seabottom sediments are raised to the surface by tectonic uplift. Also, when sea level falls during ice ages, sea bottom sediments are exposed to the atmosphere.
Pollination.....................
I’m not sure but it looks like a new born..probably 1 month old.