An important metaphysical detail, though unfortunate for the fish

G. W. Leibniz, from New System of Nature (1695):

I begin with the distinction that must be drawn between a substance and a collection, or an aggregate of several substances. When I say "me," I speak of a single substance; but an army, a herd of animals, a pond full of fish (even if it is frozen solid with all its fish) will always be a collection of several substances.