[1] The name gillaroo is derived from the Irish for "red fellow" (giolla rua); this is due to the fish's distinctive colouring.

The gillaroo is characterised by these deep red spots and a "gizzard", which is used to aid the digestion of hard food items such as water snails.

Experiments carried out by Queen's University Belfast established that the Lough Melvin fish are different from brown trout found anywhere else in the world.

[citation needed] They feed almost exclusively on bottom living animals (snails, sedge fly larva and freshwater prawns) except during late summer.

Chicken being forbidden on Fridays for members of the Catholic faith, she was so enraged she threw the entire bird into the river, whereupon it changed into a fish; hence, the "gizzard".