Acoustic scattering from fish at low frequencies is enhanced by the resonance properties of the fish swimbladder. The resonances are due to excitation of the monopole motion of the fish bladders in much the same way that bubbles resonate, and ``bubble-like'' models have been a popular method for describing resonance scattering from swimbladder bearing fish. The response of the swimbladders is strongly damped by the viscous properties of the medium surrounding the bladder, while the resonance frequency is sometimes increased above that of an air bubble of equivalent volume and appears to be influenced by the elastic properties of the swimbladder wall. In this work the method by which both elastic and viscous effects modify the physical behavior of the swimbladder is described by comparing models of bubbles with elastic shells to bubbles with viscous shells. The formalism is applied to the interpretation of experimental data.