How do cells maintain water balance through osmosis? if a salt water fish is placed in a fresh water aquarium, water will leave the fish's cells. in the experiment, the only isotonic solution was the 10% salt water solution. the egg swelled in distilled water because it is hypotonic to the egg's interior. the concentration of solute is greater inside the egg than it is in the kayro syrup. the egg swells when placed in a hypertonic solution.