GWR had names for most or all of its wagons, words that they weren't in common use that could be used over the telegraph as a shorthand for a particular wagon type. Think "Surfeit of milk churns stop. Send Syphons Soonest stop.". Someone decided to name all the engineers' wagons after different kinds of fish, and while the other names dropped away for some reason this one survived right through the BR era.Wagons - specifically applied/applies to Engineering wagons and was introduced by the GWR.