Growth of statoliths in goldfish

Abstract

Statoliths in goldfish were observed in situ from the outside of the body by an optical microscope. The shape was spheroidal in the period of embryo and fry. As the fish grew, the shape deformed into an irregular one which followed the statocyst. The statolith was a polycrystal of CaCO 3 and the crystal structure was of the aragonite type containing a very small amount of calcite. The growth rate of the statolith was 0.84 Å/s even at the maximum value, and decreased with the growth of the statolith. The degree of supersaturation of endolymph in which the statoliths grew was estimated to be 11.4. The growth of statolith in vivo was compared with that of CaCO 3 in vitro, and it is supposed that the heterogeneous nucleation occurs in endolymph frequently with random orientation on many tangled fibers, but the growth rate of statolith is decreased by the action of an inhiitor. From the above mentioned data, the surface of the statolith is considered to be rough and its surface free energy to be isotropic. Therefore, the shape will be spheroidal so as to minimize the surface free energy, when the size is small. When the statolith grows large, the shape is affected by the local concentration of endolymph and it takes an irregular form similar to the shape of a statocyst.