Holt, Ernest William Lyons (1864–1922), naturalist and antiquary, was born 17 October 1864 in London. He was educated at Eton, where he won the Biological Prize, and entering the army through Sandhurst, he joined the Duke of Cornwall's Light Infantry. He served through the Nile campaign of 1884–5 and was, unusually, promoted directly to lieutenant (1884). Afterwards he served with the mounted infantry in Egypt (1886) and in the Burmese war (1886–7), during which his health broke down and he was invalided home. After leaving the army he studied biology and became assistant to the professor of zoology at the University of St Andrews, Scotland, where he began his life's work with fishes. In 1890 he was appointed assistant-naturalist to the Rev. William Spotswood Green (qv) on a survey, organised by the RDS, of the fishing grounds off the west coast of Ireland. He made a major contribution to the success of the survey and published several papers on egg and larval stages of fish off the continental shelf.
After the survey he joined the staff of the Marine Biological Association at the laboratory at Grimsby. He had a great interest in applying scientific methodology to fisheries research, and this type of work resulted later in the founding of the International Council for the Study of the Sea. In 1894 he went to the Station Zoologique d'Endoume at Marseilles, where he published a paper on the larval development of Mediterranean fish. He then joined Plymouth marine laboratory for a period of three years, where he studied both icthyology and invertebrates.
In 1899 he returned to Ireland to take charge of the first Irish marine laboratory set up by the RDS in Ballynakill, Co. Galway, to study mackerel and salmon. The Department of Agriculture and Technical Instruction for Ireland was set up the following year and the marine laboratory was transferred into its care. He was appointed scientific advisor to the fisheries branch of the department, becoming inspector of fisheries in Galway (1908) and chief inspector in Dublin (1914).
He played an important role in the development of fisheries research in Ireland, bringing investigations into line with other countries and contributing to the work of the International Council for the Study of the Sea. The waters around Ireland were surveyed under his direction using the Helga and Helga II (which as HMS Helga had shelled Liberty Hall and other Dublin targets in 1916), and included the dredging around Clare Island, Co. Mayo, as part of the Clare Island survey (1909–11). He was also responsible for the granting of oyster and salmon licences and was seen as impartial when dealing with objections. Most of the results of his research are found in the scientific investigation reports of the fisheries branch. His interests also included salmon hatching and rearing, and the experimental breeding of oysters.
Besides his wide general knowledge of marine zoology and his sporting activities of shooting and fishing, he maintained an interest in archaeology. During his time in Galway he edited (1912–14) the Journal of the Galway Archeological and Historical Society and also contributed several papers. He lived with his sister for much of his life and socialised with the landed gentry of Galway, the Redingtons and the Persses. Copies of his correspondence with D'Arcy Wentworth Thompson (1860–1948), professor of natural history at St Andrews, are found in NUI Galway. These contain comments on some of the personalities and policies concerned with marine research in Britain and Ireland. After suffering ill health for some years he died unmarried 10 June 1922 in Chelsea, London, leaving an estate of £2,567.