Example embodiments described herein relate an integral and/or multi-piece airfoil and a shrouded fluid turbine having the same. The airfoil can have a generally circumferential body extending circumferentially about a central axis, and can be referred to herein as a “ringed airfoil.” The airfoil can have a front portion defining a leading edge of the airfoil and a rear portion defining a trailing edge of the air foil. A cross-sectional thickness of the front portion can be non-uniform and vary along a mean camber line of the airfoil from the leading edge to a transition area. A cross-sectional thickness of the rear portion can be uniform and constant along the mean camber line of the airfoil from the transition area to the trailing edge of the airfoil.