FISHERY BULLETIN: VOL. 85, NO. 3 



matrix and calcium carbonate crystals. In the de- 

 velopment of these bipartite structures, matrix 

 deposition on growing crystals is known to inter- 

 rupt further crystal growth (Wilbur 1980). This 

 results in the alternate formation of calcium-rich 

 and matrix-rich layers. In such cases, the matrix 

 may have opposite functions in controlling crystal 

 growth: as an inhibitor for the crystal growth 

 along the C-axis and as a nucleator for the forma- 

 tion of the next crystal layer (Crenshaw 1982). 

 The matrix appears to play a key role in con- 

 trolling the formation of these different layers. 

 Although this sequence is likely to be the case for 

 otolith increment formation (Wilbur 1980), the 

 rate of calcium deposition on otoliths appears to 

 be closely related to the level of serum calcium, 

 which is regulated by the action of hypercalcemic 

 and hypocalcemic hormones (Oguro and Pang 

 1982). Serum calcium has been suggested as a 

 trigger for otolith calcification through the 

 calcium-calmodulin system (Mugiya 1986). Al- 

 though Pickford (1953) found that hypophysec- 

 tomy resulted in no otolith growth in killifish, 

 what exactly controls the rate of matrix deposi- 

 tion on otoliths remains unknown. 



ACKNOWLEDGMENTS 



The author thanks David H. Secor, University 

 of South Carolina, for his thoughtful review of the 

 manuscript. This work was supported in part by 

 Grant No. 61560202 from the Educational Min- 

 istry of Japan. 



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