Abstract.Over a 15‐year period hatchery brown trout,Salmo truttaL., have been added 10 Lower Lough Erne, Northern Ireland to supplement declining native populations. Introductions have mainly comprised eyed ova and fingerlings, stocked into a number of rivers in the Erne drainage. Utilizing a natural genetic tag an electrophoretic assessment of the stocking programme was undertaken.The percentage hatchery genetic contribution in trout populations varied widely from river to river (19‐91). Lough‐caught brown trout (3+ and older) showed a substantial (21·5) hatchery genetic component. Introgression of native‐and hatchery stocks was evident. The resultant deleterious genetic consequences for the conservation of the unique Lough Erne brown trout gene pool arc discussed and alternative management strategies are
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