What is the difference in hydrogen ion concentration between hydrochloric acid and a lemon

Answer is: hydrogen ion concentration (H⁺) is greater in hydrochloric acid than a lemon with same concentration of both solutions.
Strong acids (in this example hydrochloric acid) completely ionize in water and give large amount of hydrogen ions (H⁺): HCl(aq) → H⁺(aq) + Cl⁻(aq).
Weak acids (lemon has citric acid) partially ionize in water and give only a few hydrogen ions (H⁺), in the solution there molecules of acid and ions.

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.