A seaman. A scaly fish; a rough, blunt tar. To have other fish to fry; to have other matters to mind, something else to do.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
fire shovel * fitNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes