Moriarty began a career in freelance writing while still at college. He was preparing to take a regular job at a school in England when he found an opportunity in Ireland's Department of Agriculture and Fisheries, in a studentship to observe the fish in the newly-formed
Poulaphouca Reservoir near
Blessington. He subsequently secured a permanent post, and worked in the public sector for over 40 years. While attached to the Fisheries Service (modern-day
Inland Fisheries Ireland), he was awarded an MSc at Trinity College Dublin, with a dissertation entitled "The Ecology of Irish Fresh Waters, Being a Study of Biology of Brown Trout (
Salmo trutta) and Perch (
Perca fluviatilis) in the Poulaphouca reservoir, Ireland." In 1972, he received a Ph.D from Trinity College, with a thesis entitled "The Growth and Nutrition of Fish in Ireland with Particular Reference to the Eel
Anguilla Anguilla (L.)". He gave the Went Memorial Lecture at the
Royal Dublin Society in 1987, on
The Eel in Ireland. ==Writing==