If the concentration of salt in the fluid surrounding cells decreases and the concentration of other solutes remains constant?

The cell will swell.

Explanation:

The cells react distinctly when placed in different solutions like hypertonic, isotonic and hypotonic solutions. In the mentioned question, that is, in the fluid surrounding the cells, the concentration of salt reduces, which makes the solution hypotonic. Hypotonic solution exhibit high water potential and low solute concentration.  

This makes the water move from the hypotonic solution to the inside of the cell as the osmotic movement occurs from high solvent concentration to low solvent concentration, thus, swelling of the cell takes place.  

answer; i believe the answer is hydraulic action;