Hi, thank your for posting your question here at Brainly.
The white stringy substance surrounding the fish may be one of these many choices. It could be an <span>euglena, amoeba, </span><span>water mold or </span><span>dinoflagellate. All of these are protists with the same white characteristic.</span>
Oxygen moves due to diffusion, and the diffusion of oxygen occurs from higher concentration to lower concentration that is from the blood into the tissues