What is a
atom
protons

neutrons

electrons​

Atoms are made of extremely tiny particles called protons, neutrons, and electrons.
Protons and neutrons are in the center of the atom, making up the nucleus.
Electrons surround the nucleus.
Protons have a positive charge.
Electrons have a negative charge.
The charge on the proton and electron are exactly the same size but opposite.
Neutrons have no charge.
Since opposite charges attract, protons and electrons attract each other.

I’d have to say no because without oxygen in the water the fish would all be dead. so if you want to fish for dead fish, pick the ponds with the lowest oxygen concentrations.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.