TANAKA ET AL.: EFFECTS OF PHOTOPERIOD AND FEEDING ON TILAPIA NILOTIC A 



Figure l. — Scanning electron microscope photographs of otoliths of juvenile Tilapia nilotica. A) Ground and etched otolith of a fish 28 d 

 after hatching. The core region delimited by the innermost clear discontinuous zone (arrow) shows several vague, narrow bands. The 

 center of the core region is deeply etched and has some spherules. B) Margin of a ground and etched otolith. The outermost incremental 

 zone is not complete. C) Nonetched fracture plane of an otolith. The otolith is composed of a piling up of crystallized lamellae 

 (incremental zone) with thin interstitial layers (discontinuous zone). D) Nonetched fracture plane of an otolith. The surface of a 

 complete crystallized lamella at the boundary of the interstitial layer can be seen. E) Higher magnification of the surface of the 

 crystallized lamella in D. F) Nonetched external surface of an intact otolith to show the growing surface of the outermost incremental 

 zone. 



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