The present study investigates photoinduced changes of magnetostriction in yttrium-iron garnet (YIG) single crystals. Single crystals of Y3Fe5O12 were grown from BaO-B2O3 (YIG(Ba)), PbO-PbF2 (YIG(Pb)) and PbO-PbF2:SiO2 (YIG(Si)) solutions from flux. Photoinduced magnetostrictive response types for these three kinds of YIG crystals are quite different. The magnetostrictive constants, the trigonal symmetric internal stresses and their photoinduced changes were calculated for all samples. The conclusion is that the internal stresses in the crystal lattice, caused by defects, determine the photoinduced response type of the crystal.