lateral line

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A series of sensory pores along the head and sides of fish and some amphibians by which water currents, vibrations, and pressure changes are detected.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A sense organ of a fish running lengthwise down each of its sides from the vicinity of the operculum to the base of the tail, used to detect movement and vibration in the surrounding water.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun sense organs of fish and amphibians; believed to detect pressure changes in the water