Grunion bluish-green backs and silvery sides and bellies. Their snouts are bluntly rounded and slippery. Silversides differ from true smelts of the family Osmeridae in that they lack the trout-like adipose fin. Young grunion grow rapidly and are about five inches long by the time they reach one year old and are ready to spawn. Adult fish normally range in size from with a maximum recorded size of (La Jolla, Ca., 05-11-05). Average body lengths for males and females are , respectively, at the end of one year; at the end of two years; and at the end of three years.
USS Grunion she patrolled north of Kiska Island, stated she had been attacked by a Japanese destroyer and had fired torpedoes at her with inconclusive results. She operated off Kiska throughout July and sank two enemy patrol boats as she waited for enemy shipping. On 30 July, the submarine reported intensive antisubmarine activity and was ordered back to Dutch Harbor. The "Grunion" was never heard from again. Air searches off Kiska were fruitless, and on 5 October the "Grunion" was reported overdue from patrol and assumed lost with all hands. Her name was stricken from the Naval Vessel Register on 2 November