First, in terms of etymological origins:
trull “a low prostitute or concubine; a drab, strumpet, trollop” [OED], 1510s, from German trulle, perhaps cognate with troll (n.), or perhaps from troll (v.), cf. Middle High Germantrolle “awkward fellow.”
tart (n.2) “prostitute,” 1887, from earlier use as a term of endearment to a girl or woman (1864), sometimes said to be a shortening of sweetheart. But another theory traces it to jam-tart(see tart (n.1)), which was British slang early 19c. for “attractive woman.” To tart (something) up is from 1938.
What’s obvious from these entries, once again drawn from the Online Etymology Dictionary (the other OED), is the historical journey from trull, troll, trollop to ‘tart’, the last of which emerged only in the nineteenth century. From a wallower to a follower to a juicy jam tart. Tart itself both from French ‘torte’ and from Old English ‘teart’ meaning sharp or painful and thus from the same root, via a slightly more circuitous route, as ‘austere’. Further thus, somewhere at some fork in the etymological camino, coming to signify both loose morals (as in a tart/prostitute) and severity, harshness, dryness (as in austere). Ain’t English interesting?
Troll is a whole other ‘kettle of fish,’ a puzzling phrase which http://www.phrases.org.uk explains thus:
The noun ‘kettle of fish’ is listed by several reference works as dating from 1745, although the earliest actual citation of the term in print that I [i.e Phrases UK] can find is in Thomas Newte’s A tour in England and Scotland in 1785:
“It is customary for the gentlemen who live near the Tweed to entertain their neighbours and friends with a Fete Champetre, which they call giving ‘a kettle of fish’. Tents or marquees are pitched near the flowery banks of the river… a fire is kindled, and live salmon thrown into boiling kettles.”
In art-historical terms, the ‘fete-champetre’ is a term used to refer to idyllic romps in the woods, by Giorgione or Titian, often peopled by musicians, mythological nymphs and satyrs and, in Manet’s nineteenth-century interpretation, the Dejeuner sur l’herbe, by ‘tarts’.