Fishtown was a neighborhood of Kensington District which was one of 29 municipalities which were consolidated into the City/County of Philadelphia in 1854.
The actual borders of Fishtown, like virtually all city neighborhoods, are "variable" depending on what source you consult. Many consider it the area bounded by Frankford Avenue, Norris Street, and the Delaware River. With much redelopment in process (2006) the name "Fishtown" is gaining new respect, and residents and it is now common for residents up to Lehigh Avenue to refer to their locations as Fishtown.
Campbell  writes ... "Kensington also became the textile center of Philadelphia. The section has always had a high percentage of homeowners, largely through the aid of building-loan associations, which first flourished there. Many houses are, however, subject to "irredeemable" ground rents. The river-front part was colloquailly known as Fishtown."
Frankford Avenue • Norris Street