The 190 meter long, 55496 dwt freighter Aston Trader II went aground on the San Joaquin River.   The Aston Trader II was proceeding to Stockton when it temporarily lost control and went aground.   The Coast Guard responded to the scene and an inspection showed no significant damage and no pollution being released.  Two tugs were able to free the Aston Trader II and the vessels proceeded to Stockton.   The freighter had no cargo at the time of the incident.  An investigation is being conducted.