William Robert Fish was the older brother of George Henry Fish (see entry). He was one of eleven children of Robert Fish and his wife, Hannah, nee Taylor. William Fish was born at Pleasant Creek, Stawell, Victoria in June, 1971, and was 44 and 10 months old when he enlisted at Leongatha on 12 March, 1916, about three weeks after his younger brother. At this time, He was a labourer, single and gave his mother, Hannah, as his next of kin.

William Fish was sent for training from 16 March to 25 April with the 19th Depot Battalion at Geelong, before being attached at the 14th Battalion, 8th Reinforcements at Broadmeadows on 26 April. George Fish was in the same battalion, but 18th Reinforcments. On 4 May, along with the other new recruits, the brothers embarked for England on board HMAT Port Lincoln A17. On arrival, they were sent for further training at Rollestone, before leaving for France on 23 September, 1916. 

The 14th Battalion had been raised in Melbourne and had fought at Gallipoli until the evacuation in December, 1915. They remained in Egypt until July, 1916, when they were sent to France, with their first major batle being ta Pozieres in August 1916. For the rest of the year, they remained on the Somme and it was there that the Fish brothers marched in, having landed at Etaples. On 5 October, both Fish brothers were detached from the 14th Battalion to join the 1st Canadian Tunnelling Company, one of 3o such companies set up by the Britsh coomand to dig subways and saps (narrow trenches), cable trenches, and underground chambers for medical services and signals, as well as tunnels to carry out attacks on the enemy. He was to stay with the unit until April, 1917, when he was wounded in action at Bullecourt on 11 April, 1917, with a gunshot wound to one hand. He was sent to Rouen for treatment but on 21 April, was returned to England and admitted to the 3rd General Hospital at Oxford.

Following treatment for his hand, William Fish was given furlough in England from 14 May - 29 May, 1917, when he marched in to Perham Downs for retraining with the Overseas Training Battalion. On 18 August, he returned to France and on 28 August, returned to the 14th Battalion. Then , on 29 October, he was  appointed as a Guard with the Detached Corps Safe Custody Compound. Hand wounds were notoriously difficult to deal with in those days and it is possible that his wounded hand was not strong enough to hold or load a gun, making him useless for active service at the front. In November, 1919, the 14th Battalion began the return to Australia, but William Fish stayed on and was granted UK leave from 1-10 January, 1919. Following leave, he returned to France, finally marching out for the return home on 30 May, 1919.

He returned to Australia on board HT Militiades on 19 June, 1919, disembarking in Melbourne on 5 August. he was discharged from further service on 20 September, 1919. In 1924, he was living with his brother George at 106 Charles St. Fitzroy and workign as a wood carter. In 1942, he had moved to 73 Robert St., Northcote, and was a labourer. He was still there in 1949, but the Electoral Rolls have no further mention of him. he died in 1965 at Moreland, Victoria, aged 93.